Update on Rapid Tests for COVID

Nearly a year ago, I wrote Frequent, Fast, and Cheap is Better than Sensitive, arguing for rapid antigen tests:

A number of firms have developed cheap, paper-strip tests for coronavirus that report results at-home in about 15 minutes but they have yet to be approved for use by the FDA because the FDA appears to be demanding that all tests reach accuracy levels similar to the PCR test. This is another deadly FDA mistake.

See also my posts Infected versus Infectious and Rapid Tests. The EMA and then the FDA finally did start approving these tests. So how well are they working? Pretty damn well. Canada has two innovative programs. First, in Nova Scotia pop-up clinics have been using rapid tests for asymptomatic people:

During the third wave that hit Nova Scotia over the past month, the province’s community rapid testing centres have correctly sniffed out at least 285 COVID-19 cases in asymptomatic people, or about 10 per cent of all confirmed cases in this time period, according to the Nova Scotia Health Authority.

While most provinces reserve testing only for symptomatic people or close contacts of a case, Nova Scotia’s pop-up centres allow asymptomatic people to simply show up and get a rapid test for free, with results sent to them within an hour. The whole process relies largely on volunteers without a health-care background.

Furthermore, the true number of cases credited to rapid testing is probably much higher. When a rapid test correctly identifies a positive case, the person’s close contacts such as their family get PCR lab tests that don’t show up in the rapid test statistics.

Lisa Barrett, an infectious diseases specialist and the driving force behind the rapid testing program, said it’s hard to say for certain, but taken altogether it’s possible rapid antigen testing has helped Nova Scotia find up to 18 per cent of all cases during the third wave.

“This is the early detection system,” Barrett said. Rapid testing tends to catch people early on in their infection when they’re full of virus, meaning positive cases are found and put into isolation fast — likely days before they would have been found with a PCR test, if they were found at all.

Michael Mina argues that since the rapid antigen detected cases are among the most infectious cases, detecting these cases is probably worth half of all the PCR testing.

Second, Canada’s CDL Rapid Screening Consortium is now in 200 sites with 50 large companies and rapidly expanding. A very interesting, just published paper in The Lancet runs an experiment that suggests that these testing regimes can work. The experiment rapidly tested 1000 people and the negatives were then randomly assigned either to be sent-home to conduct their regular life or to attend a multi-hour concert with masks but also singing, dancing, alcohol and no-social distancing. After 8 days there were two infections in the at-home group and no infections in the Concert group which suggests that this type of rapid testing can be used to open and keep-open concerts, schools, universities, airplanes and workplaces.

What’s the point of testing now that we have vaccines? Two reasons. First, most of the world still hasn’t been vaccinated so testing will be a very useful stop-gap measure until vaccination is more widely distributed. Indeed, the success of these programs shows what we lost by not acting more quickly a year ago. Second, although the pandemic is (essentially) over in the United States (as predicted) there will likely be an uptick in the fall among the unvaccinated and you want rapid tests to be available rapidly in hot-spots. In other words, rapid deployment of rapid tests will help us to avoid outbreaks in the future.

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