Results for “first doses”
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A Majority of Doses are Now Second Doses

As of Feb. 18 (last day of full data) we gave out 817,708 second doses and just 702,426 first doses. In other words, a majority of doses are now second doses. As Daniel Bier writes this means that we are boosting some people from ~85% to ~95% protected when we could be vaccinating more first timers and getting them from 0% protected to ~85% protected.

If we followed the British rule and delayed the booster to 12 weeks, we could immediately more than *double* the number of people going from 0% protected to to ~85% protected. More first-doses would be great for the newly protected and more people at ~85% protection would also reduce transmission so there would be fewer new infections and less threat to the non-vaccinated.

The opportunity cost of not delaying the booster is measured in lives lost.

The First Dose is Good

WSJ: The Covid-19 vaccine developed by Pfizer Inc. and BioNTech SE generates robust immunity after one dose and can be stored in ordinary freezers instead of at ultracold temperatures, according to new research and data released by the companies.

The findings provide strong arguments in favor of delaying the second dose of the two-shot vaccine, as the U.K. has done . They could also have substantial implications on vaccine policy and distribution around the world, simplifying the logistics of distributing the vaccine.

A single shot of the vaccine is 85% effective in preventing symptomatic disease 15 to 28 days after being administered, according to a peer-reviewed study conducted by the Israeli government-owned Sheba Medical Center and published in the Lancet medical journal. Pfizer and BioNTech recommend that a second dose is administered 21 days after the first.

The finding is a vindication of the approach taken by the U.K. government to delay a second dose by up to 12 weeks so it could use limited supplies to deliver a single dose to more people, and could encourage others to follow suit. Almost one-third of the U.K.’s adult population has now received at least one vaccine shot. Other authorities in parts of Canada and Europe have prioritized an initial shot, hoping they will have enough doses for a booster when needed.

Preliminary data also suggest that the other widely used vaccine in the U.K. developed by AstraZeneca PLC and the University of Oxford could have a substantial effect after a first dose .

The Israeli findings came from the first real-world data about the effect of the vaccine gathered outside of clinical trials in one of the leading nations in immunization against the coronavirus. Israel has given the first shot to 4.2 million people—more than two-thirds of eligible citizens over 16 years old—and a second shot to 2.8 million, according to its health ministry. The country has around 9.3 million citizens.

…”This groundbreaking research supports the British government’s decision to begin inoculating its citizens with a single dose of the vaccine,” said Arnon Afek, Sheba’s deputy director general.

The Israeli study is here. Data from Quebec also show that a single dose is highly effective, 80% or higher (Figure 3) in real world settings.

It’s becoming clearer that delaying the second dose is the right strategy but it was the right strategy back in December when I first started advocating for First Doses First. Waiting for more data isn’t “science,” it’s sometimes an excuse for an unscientific status-quo bias.

Approximately 16 million second doses have been administered in the US. If those doses had been first doses an additional 16 million people would have been protected from dying. Corey White estimates that every 4000 flu vaccinations saves a life which implies 4000 lives would have been saved by going to FDF. COVID, of course, is much deadlier than the flu–ten times as deadly or more going by national death figures (so including transmission and case fatality rate)– so 40,000 deaths is back of the envelope. Let’s do some more back-of-the-envelope calculations. Since Dec. 14, there have been approximately 10 million confirmed cases in the United States and 200,000 deaths. There are 200 million adults in the US so 1/1000 adults has died from COVID, just since Dec. 14. If we use 1/1000 as the risks of a random adult dying from COVID, then an additional 16 million vaccinations would have saved 16,000 lives. But that too is likely to be an underestimate since the people being vaccinated are not a random sample of adults but rather adults with a much higher risk of dying from COVID. Two to four times that number would not be unreasonable so an additional 16 million vaccinations might have avoided 32,000-64,000 deaths. Moreover, an additional 16 million first doses would have reduced transmission. None of these calculations is very good but they give a ballpark.

It is excellent news that the vaccine is stable for some time using ordinary refrigeration. Scott Duke Kominers and I argue that there is lot of unused vaccination capacity at the pharmacies and reducing the cold storage requirement will help to bring that unused capacity online. The announcement is also important for a less well understood reason. If Pfizer is only now learning that ultra-cold storage isn’t necessary then we should be looking much more closely at fractional dosing.

When I said that we should delay the second dose, people would respond with “but the companies say 21 days and 28 days! Listen to the science!”. That’s not scientific thinking but magical thinking. Listening to the science was understanding that the clinical trial regimen was designed at speed with the sole purpose of getting the vaccines approved. The clinical trial was not designed to discover the optimal regimen for public health. Don’t get me wrong. Pfizer and Moderna did the right thing! But it was wrong to think that the public health authorities could simply rely on “the science” as if it were written on stone. Even cold-storage wasn’t written on stone!  Now that the public health authorities know that the clinical trial regimen isn’t written in stone they should be more willing to consider policies such as delaying the second dose and fractional dosing.

We are nearing the end in the US but delaying the second dose and other dose-stretching policies are going to be important in other countries.

Half Doses of Moderna Produce Neutralizing Antibodies

A new phase II study from Moderna shows that half-doses (50 μg) appear to be as good as full doses (100 ug) at generating correlates of protection such as neutralizing antibodies.

In this randomized, controlled phase 2 trial, the SARS-CoV-2 vaccine candidate mRNA-1273, administered as a two-dose vaccination regimen at 50 and 100 μg, exhibited robust immune responses and an acceptable safety profile in healthy adults aged 18 years and older. Local and systemic adverse reactions were mostly mild-to-moderate in severity, were ≤4 days of median duration and were less commonly reported in older compared with younger adults. Anti-SARS-CoV-2 spike binding and neutralizing antibodies were induced by both doses of mRNA-1273 within 28 days after the first vaccination, and rose substantially to peak titers by 14 days after the second vaccination, exceeding levels of convalescent sera from COVID-19 patients. The antibodies remained elevated through the last time point assessed at 57 days. Neutralizing responses met criteria for seroconversion within 28 days after the first vaccination in the majority of participants, with rates of 100% observed at 14 and 28 days after the second vaccination. While no formal statistical testing was done, binding and neutralizing antibody responses were generally comparable in participants who received the 100 μg mRNA-1273 and the 50 μg dose at all time points and across both age groups. Overall, the results of this randomized, placebo-controlled trial extend previous immunogenicity and safety results for mRNA-1273 in the phase 1 study in an expanded cohort including participants older than 55 years of age [16, 19].

[These data] confirm that a robust immune response is generated at both 50 and 100 ug dose levels.

As I wrote earlier, halving the dose is equivalent to instantly doubling the output of every Moderna factory.

See my piece in the Washington Post on getting to V-day sooner for an overview of dose stretching strategies.

Addendum: France says one dose is sufficient for previously COVID infected.

“Second Doses” post-mortem

The most striking thing about the Biden administration shift to a version of “First Doses First” is how little protest there has been.  Given how many public health experts were upset about the idea only a few days ago, you might expect them to organize a Wall Street Journal petition from hundreds of their colleagues: “Biden administration proposal endangers the lives of millions of Americans.”

But of course they won’t do that.  Some of that is pro-Democrat partisanship, but that is not even the main factor.  One reason is that public health experts, with their medical and quasi-medical backgrounds, typically have very little sense of how to respond in the public arena if challenged.  For instance, not a single one stepped forward with a calculation to defend “Second Doses.”  They are not especially good at “the internet rules of the game,” which of course are now supreme (not always for the best, to be clear).

The second and probably most important reason is that, as I had explained, sins of omission are treated as far less significant than sins of commission.  Now that a version of “First Doses First” is on the verge of becoming policy, to do nothing about that is only a sin of omission, and thus not so bad.  Remarkable!  Status quo bias really matters here.

I haven’t seen a single peep on Twitter opposing the new policy.

Just keep all this in mind the next time you see a debate over public health policy.  There is often less behind the curtain than you might think.

Half-Doses as Good as Full?

NYTimes: A top official of Operation Warp Speed floated a new idea on Sunday for stretching the limited number of Covid-19 vaccine doses in the United States: Halving the dose of each shot of Moderna’s vaccine to potentially double the number of people who could receive it.

Data from Moderna’s clinical trials demonstrated that people between the ages of 18 and 55 who received two 50-microgram doses showed an “identical immune response” to the standard of two 100-microgram doses, said the official, Dr. Moncef Slaoui.

Dr. Slaoui said that Operation Warp Speed was in discussions with the Food and Drug Administration and the pharmaceutical company Moderna over implementing the half-dose regimen. Moderna did not respond immediately to a request for comment.

Each vaccine would still be delivered in two, on-schedule doses four weeks apart, Dr. Slaoui said in an interview with “CBS’s Face the Nation.” He said it would be up to the F.D.A. to decide whether to move forward with the plan.

Half dosing would double Moderna doses permanently rather than temporarily (as with First Doses First). Thus, I would be very happy to see half-dosing and it would obviate the need for FDF.

I and a handful of others started to discuss and advocate First Doses First on Dec. 8 and many times since then. The advocacy was then joined by Tony Blair and by many epidemiologists, immunologists, vaccine researchers, physicians and public health experts as well, of course, by the British experts on the Joint Committee on Vaccination and Immunisation. It’s clear that the FDA and Operation Warp Speed are now feeling the pressure to take some serious actions to increase supply. If so, my small efforts will have had a very high return.

Keep the pressure on.

Addendum: By the way, the British have yet to approve the Moderna vaccine (probably because they can’t get doses for some time anyway) and the AstraZeneca vaccine appears to work better with a longer dosing interval. So FDF makes sense for the British and we can do half-dosing on Moderna, potentially setting a new and beneficial standard for the entire world.

First Dose First

Writing on twitter Keith Klugman, world expert on infectious diseases and director of the Gates Foundation Pneumonia program, supports a policy I have argued for–First Doses First.

First doses of Pfizer/Moderna vaccines are 90%+ effective after 14 days. Most high risk lives will be saved by giving all these limited early supplies of vaccine as first doses – second doses can be given later if first dose effectiveness wanes or when supply improves

Here’s a way of thinking about this policy. Suppose you are scheduled for your second dose of the Pfizer or Moderna vaccine but you have the option of giving your second dose to your spouse as their first dose. Would you?

If the answer is yes then can you ethically deny this to someone else’s spouse?

Keep in mind that we have at least three more vaccines that could be available in as little as 12 weeks, Astra-Zeneca, Johnson & Jonson and Novavax. We are also pushing for more doses from Pfizer and we should be willing to pay top-dollar for those doses. As those vaccines come online we can deliver second doses.

Addendum: If you are 75 and your spouse is 25 then maybe you wouldn’t give your second dose to your spouse and that too ought to help us think about the larger questions of allocation.

The case for geographically concentrated vaccine doses

Here goes:

A central yet neglected point is that vaccines should not be sent to each and every part of the U.S. Instead, it would be better to concentrate distribution in a small number of places where the vaccines can have a greater impact.

Say, for the purposes of argument, that you had 20,000 vaccine doses to distribute. There are about 20,000 cities and towns in America. Would you send one dose to each location? That might sound fair, but such a distribution would limit the overall effect. Many of those 20,000 recipients would be safer, but your plan would not meaningfully reduce community transmission in any of those places, nor would it allow any public events to restart or schools to reopen.

Alternatively, say you chose one town or well-defined area and distributed all 20,000 doses there. Not only would you protect 20,000 people with the vaccine, but the surrounding area would be much safer, too. Children could go to school, for instance, knowing that most of the other people in the building had been vaccinated. Shopping and dining would boom as well.

Here is one qualifier, but in fact it pushes one further along the road to geographic concentration:

Over time, mobility, migration and mixing would undo some of the initial benefits of the geographically concentrated dose of vaccines. That’s why the second round of vaccine distribution should go exactly to those people who are most likely to mix with the first targeted area. This plan reaps two benefits: protecting the people in the newly chosen second area, and limiting the ability of those people to disrupt the benefits already gained in the first area.

In other words, if the first doses went (to choose a random example) to Wilmington, Delaware, the next batch of doses should go to the suburbs of Wilmington. In economics language [behind this link is a highly useful Michael Kremer paper], one can say that Covid-19 infections (and protections) have externalities, and there are increasing returns to those externalities. That implies a geographically concentrated approach to vaccine distribution, whether at the federal or state level.

Here is another qualifier:

…there will be practical limits on a fully concentrated geographic distribution of vaccines. Too many vaccines sent to too few places will result in long waits and trouble with storage. Nonetheless, at the margin the U.S. should still consider a more geographically concentrated distribution than what it is likely to do.

Do you think that travel restrictions have stopped the spread of the coronavirus? (Doesn’t mean you have to favor them, all things considered.)  Probably yes.  If so, you probably ought to favor a geographically concentrated initial distribution of the vaccine as well — can you see why it is the same logic?  Just imagine it spreading out like stones on a Go board.

Of course we are not likely to do any of this.  Here is my full Bloomberg column.

Extreme carcinogenic doses for rats

Here is a defense of using those rat tests to judge what will cause cancer in humans:

The "junk science" they are referring to is the long-standing and
well-confirmed practice of identifying chemicals likely to cause cancer
in humans by testing them in animals. The animals (rodents) are a
standard model for biological processes of relevance to humans (which
is why drug companies and medical researchers have been using them for
a century). They are well understood and are the only sentinels for
detecting carcinogenicity of any use to public health. Since chemically
induced cancer has a latency period of decades (typically 20 years or
more), waiting for it to appear in human populations would meant that
once detected, even if exposure would cease instantly (which can never
happen), it would take another 20 or more years to eliminate the
cancers from exposure (all the cancers induced in the 20 years exposure
prior to detection). But even then, the chances of detecting any but
the most powerful carcinogens in human populations (via epidemiology)
is small. Epidemiology is a very insensitive tool. I say this with some
authority, as I am a cancer epidemiologist specializing in chemical
exposures and have authored numerous peer reviewed studies in that area
over many years.

The main rhetorical lever ACSH employs is the
use of high doses in the animal studies, doses that are much higher
than usually faced by humans. But as ACSH knows well (but didn’t
divulge) there is a technical requirement for using these doses. If one
were to use doses in animals predicted to cause cancer at a rate we
would consider a public health hazard, we would need tens of thousands
of animals to test a single dose, mode of exposure and rodent species
or strain. This makes using those doses infeasible. Thus a Maximum
Tolerated Dose is used, one that causes no other pathology except
possibly cancer and doesn’t result in more than a 10% weight loss. The
assumption here is that something that causes cancer at high doses in
these animals will also do so at low doses. This is biologically
reasonable. It is a (surprising) fact, that most chemicals, given in no
matter how high a dose, won’t cause the very unusual and specific
biological effect of turning an animal cell cancerous. Cancer cells are
not "damaged" cells in the individual sense but "super cells," capable
of out competing normal cells. It is only in the context of the whole
organism that there is a problem. It is not surprising, then, that very
few chemicals would have be ability to turn a normal cell into a
biological super cell of this type. Estimates are that is far less than
10%, perhaps only 1% of all chemicals that have this ability. Thus
western industrial civilization doesn’t have to come to a screeching
halt if we eliminate industrial chemical carcinogens from our
environment.

We know of no false negatives with this process.
Every chemical we know that causes cancer in humans also does so in
rodents (with the possible exception of inorganic trivalent arsenic,
which is equivocal).

Here is the full post.  I’m not close to having the expertise to evaluate these claims, but two points.  First, the author is highly qualified; as a blogger he is anonymous but I can vouch for his credentials.  Second, it should be the self-appointed task of bloggers to pass along arguments which either struck them or which might shake up their readers.

A Half Dose of Moderna is More Effective Than a Full Dose of AstraZeneca

Today we are releasing a new paper on dose-stretching, co-authored by Witold Wiecek, Amrita Ahuja, Michael Kremer, Alexandre Simoes Gomes, Christopher M. Snyder, Brandon Joel Tan and myself.

The paper makes three big points. First, Khoury et al (2021) just published a paper in Nature which shows that “Neutralizing antibody levels are highly predictive of immune protection from symptomatic SARS-CoV-2 infection.” What that means is that there is a strong relationship between immunogenicity data that we can easily measure with a blood test and the efficacy rate that it takes hundreds of millions of dollars and many months of time to measure in a clinical trial. Thus, future vaccines may not have to go through lengthy clinical trials (which may even be made impossible as infections rates decline) but can instead rely on these correlates of immunity.

Here is where fractional dosing comes in. We supplement the key figure from Khoury et al.’s paper to show that fractional doses of the Moderna and Pfizer vaccines have neutralizing antibody levels (as measured in the early phase I and phase II trials) that look to be on par with those of many approved vaccines. Indeed, a one-half or one-quarter dose of the Moderna or Pfizer vaccine is predicted to be more effective than the standard dose of some of the other vaccines like the AstraZeneca, J&J or Sinopharm vaccines, assuming the same relationship as in Khoury et al. holds. The point is not that these other vaccines aren’t good–they are great! The point is that by using fractional dosing we could rapidly and safely expand the number of effective doses of the Moderna and Pfizer vaccines.

Second, we embed fractional doses and other policies such as first doses first in a SIER model and we show that even if efficacy rates for fractional doses are considerably lower, dose-stretching policies are still likely to reduce infections and deaths (assuming we can expand vaccinations fast enough to take advantage of the greater supply, which is well within the vaccination frontier). For example, a half-dose strategy reduces infections and deaths under a variety of different epidemic scenarios as long as the efficacy rate is 70% or greater.

Third, we show that under plausible scenarios it is better to start vaccination with a less efficacious vaccine than to wait for a more efficacious vaccine. Thus, Great Britain and Canada’s policies of starting First Doses first with the AstraZeneca vaccine and then moving to second doses, perhaps with the Moderna or Pfizer vaccines is a good strategy.

It is possible that new variants will reduce the efficacy rate of all vaccines indeed that is almost inevitable but that doesn’t mean that fractional dosing isn’t optimal nor that we shouldn’t adopt these policies now. What it means is that we should be testing and then adapting our strategy in light of new events like a battlefield commander. We might, for example, use fractional dosing in the young or for the second shot and reserve full doses for the elderly.

One more point worth mentioning. Dose stretching policies everywhere are especially beneficial for less-developed countries, many of which are at the back of the vaccine queue. If dose-stretching cuts the time to be vaccinated in half, for example, then that may mean cutting the time to be vaccinated from two months to one month in a developed country but cutting it from two years to one year in a country that is currently at the back of the queue.

Read the whole thing.

The Becker-Friedman center also has a video discussion featuring my co-authors, Nobel prize winner Michael Kremer and the very excellent Witold Wiecek.

Two Vaccine Updates

First, in an article on new vaccine boosters in USA today there is this revealing statement:

Any revised Moderna vaccine would include a lower dose than the original, Moore said. The company went with a high dose in its initial vaccine to guarantee effectiveness, but she said the company is confident the dose can come down, reducing side effects without compromising protection.

Arrgh! Why wait for a new vaccine??? Fractional dosing now!

A microneedle patch for vaccines.

The same article also notes:

One of Moderna’s co-founders, MIT professor Robert Langer, is known for his research on microneedles, tiny Band-Aid-like patches that can deliver medications without the pain of a shot. Moderna has said nothing about delivery plans, but it’s conceivable the company might try to combine the two technologies to provide a booster that doesn’t require an injection.

The skin is highly immunologically active so you can give lower doses with a microneedle patch. The microneedles are sometimes made from sugar and don’t hurt. Microneedle delivery, however, can cause scars but I say apply the patch where the sun don’t shine and let’s go!

Second, Canada’s NACI has now endorsed mix and match for the AZ and Pfizer and Moderna vaccines. First Doses First has put Canada in very good shape (now ahead of the US in percent of the population with at least one dose) and this was always part of the FDF plan–delay second doses to get out more first doses and then, when supplies increase, give second doses, possibly with a better vaccine.

India Delays the 2nd Dose; Delaying 2nd Dose Improves Immune Response; Fractional Dosing

India has delayed the second dose to 12-16 weeks.

In other news, delaying the second dose of the Pfizer vaccine appears to improves the immune response (as was also found for the AstraZeneca vaccine). The latter is a news report based on a press release so some caution is warranted but frankly this was always the Bayesian bet since most vaccines have a longer time between doses as that helps the immune system. As Tyler and myself both argued, the short gap between the first and second dose was chosen to speed up the clinical trials not to maximize immunity. That was the right decision in the emergency but it was never the case that following the clinical trial regimen was “going by the science” no matter what Fauci said.

Many lives have been lost by not going to first doses first earlier, both here and in India.

Every country should move to a regimen in which the second dose comes at 12-16 weeks, even the United States, as this may improve the immune response and help other countries get a little bit ahead in their vaccine drives.

May I now also beat the drum some more on fractional dosing? Many people (not everyone) report that the second mRNA dose packs a wallop. I suspect that a half dose at 12-16 weeks would be plenty and that would free up significant capacity to vaccinate more people with first doses. We could also run some trials on half-doses for the young as a way to balance dosing and risk. Again this will matter for the rest of the world more than the United States but stretching doses in the United States will help the rest of the world and the arguments against stretching doses are now much diminished.

Atul Gawande and Zeke Emanuel Now Support Delaying the Second Dose

Many people are coming around to First Doses First, i.e delaying the second dose to ~12 weeks. Atul Gawande, for example, tweeted:

As cases and hospitalizations rise again, we can’t count on behavior alone reversing this course. Therefore, it’s time for the Biden admin to delay 2nd vax doses to 12 weeks. Getting as many people as possible a vax dose is now urgent.

Now urgent??? Yes, I am a little frustrated because the trajectory on the new variants was very clear. On January 1, for example, I wrote about The New Strain and the Need for Speed (riffing off an excellent piece by Zeynep Tufekci).  Still, very happy to have Gawande’s voice added to the cause. Also joining Gawande are the power trio of Govind Persad, William F. Parker and Ezekiel J. Emanuel who in an important op-ed write:

If we temporarily delay second doses …that is our best hope of quelling the fourth wave ignited by the B.1.1.7 variant. Because we did not start this strategy earlier, it is probably too late for Michigan, New York, New Jersey and the other Northeastern states. But it might be just in time for the South and California — the next places the more infectious strain will go if historical patterns repeat.

…Drug manufacturers selected the three- or four-week interval currently used between doses to rapidly prove efficacy in clinical trials. They did not choose such short intervals based on the optimal way of using the vaccines to quell a pandemic. While a three- or four-week follow-up is safe and effective, there is no evidence it optimizes either individual benefit or population protection.

…Some complain that postponing second doses is not “following the science.” But the scientific evidence goes far beyond what was shown in the original efficacy trials. Data from the United Kingdom, Israel and now the Centers for Disease Control and Prevention shows that first doses both prevent infection and reduce transmission. In people with prior infection, experts are beginning to recognize that a second dose could provide even less benefit. Following the science means updating policies to recognize new evidence rather than stubbornly maintaining the status quo.

Emanuel is on Biden’s COVID-19 task force so consider this op-ed running the flag up the flagpole. I predict Topol will fall next.

I would be surprised, however, if the US changes course now–too many people would then ask why didn’t we do this sooner?–but dose stretching is going to be important for the rest of the world. Why aren’t we doing more to investigate fractional dosing? Even if we went to half-doses on the second dose–the full second dose appears to be strong–that would still be a significant increase in total supply.

Addendum: I have argued for sending extra doses to Michigan and other hot spots such as NJ. Flood the zone! The Biden administration says no. Why? Production is now running well ahead of distribution as more than 50 million doses have been delivered but not administered. It would be a particularly good idea to send more single-shot J&J to reach hard to reach communities–one and done.

Power Up!

Two weeks ago I was bitten by the equivalent of a radioactive spider and now I have superpowers! Including the power of immunity and the power to fly! Awesome. As I said earlier, the SARS-COV-2 virus killed more people this year than bullets “so virus immunity is a much better superpower than bullet immunity!”

I got the J&J vaccine–one of the first in the world to do so–which seemed appropriate as I have been calling for first doses first and the J&J vaccine is single dose. I will probably supplement with Novavax at a later date when supplies are plentiful.

Addendum: Also, I can get free donuts at Krispy Kreme.

British Vaccine Efficiency

The British vaccination plan has been run very well. As this audience knows, the British delayed the second dose in order to get out more first doses quickly. A life-saving move. The British have also been targeting age and riskier workers very well. The excellent Witold Więcek (an Emergent Ventures prize recipient) has done a back of the envelope calculation which indicates how well the British are targeting.

Since the vaccines have been prioritised for the elderly, the infection fatality risk (IFR) for a typical vaccinated patient is higher than the average IFR in the population. However, we have to account for the fact that many of the early doses are given to health care workers and some of the other key workers. By late February 2021, in the UK around 55% of the vaccines went to people over 70 and over 95% of that age group has been vaccinated. In the US, however, while 55% of vaccines went to people over 65, close to 30% went to people younger than 50. We calculated IFR as an approximate weighted mean of age-specific infection mortality risks, using a meta-analysis estimate in Manheim et al., 2021.

Applying this IFR approach to real-world distributions of vaccine distribution, for UK we obtained 4.7% and for the US 3.2%, a remarkable difference. In other words, despite delivering twice the number of doses (and “running out” of highest risk individuals to vaccinate), a single dose of vaccine in the UK was still used 50% more effectively than in the US. (It should be noted, however, that the UK has a slightly older population than the US.)

Given less centralized health information, it’s hard to see how the US could target much better while also maintaining speed which is why, after the first round of vaccinating the nursing homes and the very elderly, I have leaned towards opening up more vaccination sites and prioritizing speed. So read this as a credit to the British rather than a demerit to the US. Other European countries, however, also have more centralized medical systems and yet have been far behind the British. It has struck me during this crisis how little these kind of system-wide policy variable seem to explain in the efficiency of the pandemic response overall.

Dose Stretching Policies Probably *Reduce* Mutation Risk

One objection to dose-stretching policies, such as delaying the second dose or using half-doses, is that this might increase the risk of mutation. While possible, some immunologists and evolution experts are now arguing that dose-stretching will probably reduce mutation risk which is what Tyler and I concluded. Here’s Tyler:

One counter argument is that letting “half-vaccinated” people walk around will induce additional virus mutations.  Florian Kramer raises this issue, as do a number of others.

Maybe, but again I wish to see your expected value calculations.  And in doing these calculations, keep the following points in mind:

a. It is hard to find vaccines where there is a recommendation of “must give the second dose within 21 days” — are there any?

b. The 21-day (or 28-day) interval between doses was chosen to accelerate the completion of the trial, not because it has magical medical properties.

c. Way back when people were thrilled at the idea of Covid vaccines with possible 60% efficacy, few if any painted that scenario as a nightmare of mutations and otherwise giant monster swarms.

d. You get feedback along the way, including from the UK: “If it turns out that immunity wanes quickly with 1 dose, switch policies!”  It is easy enough to apply serological testing to a control group to learn along the way.  Yes I know this means egg on the face for public health types and the regulators.

e. Under the status quo, with basically p = 1 we have seen two mutations — the English and the South African — from currently unvaccinated populations.  Those mutations are here, and they are likely to overwhelm U.S. health care systems within two months.  That not only increases the need for a speedy response, it also indicates the chance of regular mutations from the currently “totally unvaccinated” population is really quite high and the results are really quite dire!  If you are so worried about hypothetical mutations from the “half vaccinated” we do need a numerical, expected value calculation comparing it to something we already know has happened and may happen yet again.  When doing your comparison, the hurdle you will have to clear here is very high.

(See my Washington Post piece for similar arguments and additional references.).

Now here are evolutionary theorists, immunologists and viral experts Sarah Cobey, Daniel B. Larremore, Yonatan H. Grad, and Marc Lipsitch in an excellent paper that first reviews the case for first doses first and then addresses the escape argument. They make several interrelated arguments that a one-dose strategy will reduce transmission, reduce prevalence, and reduce severity and that all of these effects reduce mutation risk.

The arguments above suggest that, thanks to at least some effect on transmission from one dose, widespread use of a single dose of mRNA vaccines will likely reduce infection prevalence…

The reduced transmission and lower prevalence have several effects that individually and together tend to reduce the probability that variants with a fitness advantage such as immune escape will arise and spread (Wen, Malani, and Cobey 2020). The first is that with fewer infected hosts, there are fewer opportunities for new mutations to arise—reducing available genetic variation on which selection can act. Although substitutions that reduce antibody binding were documented before vaccine rollout and are thus relatively common, adaptive evolution is facilitated by the appearance of mutations and other rearrangements that increase the fitness benefit of other mutations (Gong, Suchard, and Bloom 2013; N. C. Wu et al. 2013; Starr and Thornton 2016). The global population size of SARS-CoV-2 is enormous, but the space of possible mutations is larger, and lowering prevalence helps constrain this exploration. Other benefits arise when a small fraction of hosts drives most transmission and the effective reproductive number is low. Selection operates less effectively under these conditions: beneficial mutations will more often be lost by chance, and variants with beneficial mutations are less certain to rise to high frequencies in the population (Desai, Fisher, and Murray 2007; Patwa and Wahl 2008; Otto and Whitlock 1997; Desai and Fisher 2007; Kimura 1957). More research is clearly needed to understand the precise impact of vaccination on SARS-CoV-2 evolution, but multiple lines of evidence suggest that vaccination strategies that reduce prevalence would reduce rather than accelerate the rate of adaptation, including antigenic evolution, and thus incidence over the long term.

In evaluating the potential impact of expanded coverage from dose sparing on the transmission of escape variants, it is necessary to compare the alternative scenario, where fewer individuals are vaccinated (but a larger proportion receive two doses) and more people recover from natural infection. Immunity developing during the course of natural infection, and the immune response that inhibits repeat infection, also impose selection pressure. Although natural infection involves immune responses to a broader set of antibody and T cell targets compared to vaccination, antibodies to the spike protein are likely a major component of protection after either kind of exposure (Addetia et al. 2020; Zost et al. 2020; Steffen et al. 2020), and genetic variants that escape polyclonal sera after natural infection have already been identified (Weisblum et al. 2020; Andreano et al. 2020). Studies comparing the effectiveness of past infection and vaccination on protection and transmission are ongoing. If protective immunity, and specifically protection against transmission, from natural infection is weaker than that from one dose of vaccination, the rate of spread of escape variants in individuals with infection-induced immunity could be higher than in those with vaccine-induced immunity. In this case, an additional advantage of increasing coverage through dose sparing might be a reduction in the selective pressure from infection-induced immunity.

…In the simplest terms, the concern that dose-sparing strategies will enhance the spread of immune escape mutants postulates that individuals with a single dose of vaccine are those with the intermediate, “just right” level of immunity, more likely to evolve escape variants than those with zero or two doses (Bieniasz 2021; Saad-Roy et al. 2021)….There is no particular reason to believe this is the case. Strong immune responses arising from past infection or vaccination will clearly inhibit viral replication, preventing infection and thus within-host adaptation…. Past work on influenza has found no evidence of selection for escape variants during infection in vaccinated hosts (Debbink et al. 2017). Instead, evidence suggests that it is immunocompromised hosts with prolonged influenza infections and high viral loads whose viral populations show high diversity and potentially adaptation (Xue et al. 2017, 2018), a phenomenon also seen with SARS-CoV-2 (Choi et al. 2020; Kemp et al. 2020; Ko et al. 2021). It seems likely, given its impact on disease, that vaccination could shorten such infections, and there is limited evidence already that vaccination reduces the amount of virus present in those who do become infected post-vaccination (Levine-Tiefenbrun et al. 2021).

I also very much agree with these more general points:

The pandemic forces difficult choices under scientific uncertainty. There is a risk that appeals to improve the scientific basis of decision-making will inadvertently equate the absence of precise information about a particular scenario with complete ignorance, and thereby dismiss decades of accumulated and relevant scientific knowledge. Concerns about vaccine-induced evolution are often associated with worry about departing from the precise dosing intervals used in clinical trials. Although other intervals were investigated in earlier immunogenicity studies, for mRNA vaccines, these intervals were partly chosen for speed and have not been completely optimized. They are not the only information on immune responses. Indeed, arguments that vaccine efficacy below 95% would be unacceptable under dose sparing of mRNA vaccines imply that campaigns with the other vaccines estimated to have a lower efficacy pose similar problems. Yet few would advocate these vaccines should be withheld in the thick of a pandemic, or roll outs slowed to increase the number of doses that can be given to a smaller group of people. We urge careful consideration of scientific evidence to minimize lives lost.