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How — and When — We’ll Know If a Covid-19 Vaccine Is Working
Phase 3 trials explained
There are more than 150 experimental Covid-19 vaccines in development right now, and a handful of those have recently entered the final stages of human testing.
Initial findings show a glimmer of promise: In early trials, these vaccines appear safe and seem to spur an immune response in the body. But how will we know that a vaccine is actually working? And how soon could that be?
Despite President Trump’s rosy predictions that a vaccine will be ready by Election Day on November 3, experts say that timeline is unlikely.
“I don’t see how that’s possible,” said Paul Offit, MD, director of the Vaccine Education Center at Children’s Hospital of Philadelphia, during a National Press Foundation briefing for journalists on August 10. “I think that would be a mistake. You want to make sure that we have clear efficacy data before we put this vaccine out there, because there is fragile vaccine confidence in this country.”
Moderna and Pfizer kicked off late-stage trials at the end of July, with both companies hoping to enroll 30,000 people. In an Aug. 7 email from Moderna obtained by CNN, investigators said they have so far enrolled 4,536 trial subjects. Meanwhile, AstraZeneca is expected to begin a large trial in the U.S. soon. It will take time to screen people to first learn whether they’re eligible to participate. Plus, the vaccines being tested by these companies each require two doses, an initial shot and a “booster” given about a month later.
After that, researchers will need to follow people for several weeks to learn whether they get sick with Covid-19 while going about their daily lives. Investigators will also need to take blood samples from people and analyze them for antibodies against SARS-CoV-2, the virus that causes Covid-19. Specifically, they’re hoping that a vaccine prompts the body into making antibodies that can neutralize the virus. Looking for neutralizing antibodies is more…
