Doctors warn that releasing a vaccine prematurely can do more harm than good.
By Jane E. Brody
Under normal circumstances, this process takes years. But these are not normal times, so the testing of potential Covid-19 vaccines is being collapsed into months, which could increase the risk of foul-ups. However, Dr. Francis Collins, director of the National Institutes of Health, gave his word that, despite being in a hurry to get an effective vaccine to the public, “we will not compromise on safety.”
Here’s how Dr. Offit, who is involved in supervising the Covid vaccine trials, described the necessary sequence of events:
A prospective vaccine is first tested on laboratory animals that normally develop Covid-19 when infected with the virus, such as mice, to see if it prevents the disease. This is called “proof of concept” that the vaccine can work. It is followed by Phase I and Phase II trials in perhaps hundreds or thousands of human volunteers. Researchers look for evidence that the vaccine is safe, and test different vaccine doses to find one that best results in antibodies that could protect against the virus. At least two vaccine candidates are already in this stage.
Now comes the big test, Phase III, a prospective placebo-controlled trial of tens of thousands of individuals to assess both safety and effectiveness. For one or more of the five promising Covid vaccine candidates being fast-tracked, this stage is expected to start in July. Each Phase III trial will entail 20,000 people who get the experimental vaccine and a control (placebo) group of 10,000 unvaccinated people. The trials will take place in areas here and abroad that are already, or expected to be, “hot spots” for Covid infections.
But depending on how prevalent the virus is this summer where the trials take place, it could take months — or even a year — to determine how well the vaccine prevents disease.
“That’s the only way to know if the immune response seen in earlier trials is protective in the real world,” Dr. Offit said. “If there’s little disease over the summer, it could be a problem. We may have to keep recruiting participants until enough people in the placebo group got sick to have a meaningful comparison with the vaccinated group. We can’t short-circuit the process.”
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