Early evidence that any vaccine works would lead to political pressure from the administration for emergency approval by the Food and Drug Administration. That conflict between science and politics might cause some people to not trust the vaccine and refuse to take it, which would undermine the global campaign to stop the pandemic. Or it could lead to a product that is not fully protective. Confidence in routine childhood vaccinations, already shaken, could decline further.
On Monday at 6:45 a.m., the first volunteer in the landmark phase 3 trial for the Moderna Therapeutics vaccine received a shot at a clinic in Savannah, Georgia. Clinicians at 88 other sites, stretching from Miami to Seattle, were also preparing to deliver the experimental shot in a trial that aims to enroll 30,000 people.
Another vaccine, produced by Pfizer with the German company BioNTech, also entered a large phase 3 U.S. trial this week. It's being tested independently of the National Institutes of Health, which is partially funding the Moderna trial as well as tests for an Oxford University/AstraZeneca vaccine trial, and others in the future. AstraZeneca has said some doses of its vaccine might be ready as early as September.
Fauci said he expects the Moderna trial to provide an answer about whether that vaccine works by the end of the year — and it's "conceivable" an answer could come in October. "I doubt that, but we are leaving an open mind that it is a possibility."
In theory, scientists might get a handle on a vaccine's efficacy before all 30,000 people are enrolled, vaccinated and studied.In fact, an answer could become clear after only 150 to 160 cases of disease are reported among the trial participants, Fauci said. If roughly two-thirds of those cases occurred in non-vaccinated people, it would show statisticians that the vaccine had above-60% efficacy, he said.
If the vaccine is 80% to 90% effective and the annual rate of infection in the places where it's being tested is above 4%, scientists could get a signal of efficacy in such a trial with just 50 cases, or in as little as three months.The public might clamor for the release of any vaccine that seemed to work. Moderna said it has already begun producing millions of doses of vaccine "at risk," banking on the vaccine's success. The FDA could release those under powers provided when the country declared a public health emergency in March.
Experts also worry about releasing a vaccine that shows some positive effects but isn't robustly protective. A slide presented by FDA deputy director Philip Krause at the World Health Organization earlier this month said a weak vaccine could fail to protect the public adequately, leading to a false sense of security in those who've received it, while making it harder to test future vaccines.