Theory and data both suggest that a much smaller dose–perhaps as low as 1/4 the current dose—of both the Moderna and Pfizer vaccines are as effective as a larger dose. Half doses of Moderna and Pfizer would be equivalent to instantly doubling the number of Moderna and Pfizer factories and would save hundreds of thousands of lives and be worth hundreds of billions of dollars in world GDP. Clinical data from adults 18-55 from the Moderna Phase II trial already suggest that quarter-doses are effective, which is why Operation Warp Speed chief, Moncef Slaoui has advocated for half-doses (leaving plenty of margin).
“We know that, for the Moderna vaccine, giving half of the dose to people between the ages of 18 and 55, two doses [at] half the dose … we know it induces identical immune response” to the currently authorized dose, Slaoui added.
Another way of putting this is that new clinical trials on dosing would be tremendously valuable. Ideally, we could use correlates of protection and do a bridging trial to infer the effectiveness of half-doses. The FDA has already said they will accept a bridging trial for new mRNA vaccines for variants, which is the right decision. The FDA should also accept a bridging trial for new dosing.
If new clinical trials are deemed necessary, dosing trials could be run as challenge trials but instead of comparing half-doses to placebo we would compare full-doses to half-doses. Thus, everyone in the challenge trial would be vaccinated, massively lowering risks. If we can’t do challenge trials even with vaccinated volunteers (!) then let’s get started on clinical trials. The NIH created the ACTIV program to speed clinical trials. Use it.
New clinical trials are valuable not just for dosing but also for approving new vaccines. Equivalence trials on the Sputnik and Sinopharm vaccines, for example, could be very valuable. In other words, we would trial Sputnik and Sinopharm against Pfizer and Moderna. A lot of people would be quite willing to join a trial in which the worst outcome is most likely getting a somewhat less effective vaccine–that’s much better than no vaccine!
The value of experiments, or let’s call them pilot studies, right now is immense. We can do pilot studies on half dosing for Moderna and Pfizer vaccines much faster and cheaper than we can build twice as many factories. So let’s do it!