In a U.S. pandemic response dominated by missteps, the effort to develop vaccines to prevent Covid-19 has so far been a triumph. Vaccines against the coronavirus that causes the disease are now racing through giant clinical trials as a result.
It’s a terrible irony, then, that the Trump administration’s statements have resulted in an erosion of public trust, with the percent of Americans who tell pollsters they would take a Covid-19 vaccine dropping and experts worrying the president could compel the Food and Drug Administration to approve a vaccine before one is ready. (Spoiler: No vaccine will likely be ready by Election Day.)
“When the the president comes out and says, ‘by a very special day, we might have a vaccine,’ the whole thing blows up,” Ashish Jha, the dean of the Brown School of Public Health, said at a session focused on Covid-19 at the STAT Health Tech Summit. “In some ways, we’ve got to get the politicians to shut up and let the scientists talk about this and drive this process.”
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The process of deciding when a vaccine appears to be safe and effective isn’t as straightforward as the general public might believe. But it’s important to understand it if we are to have confidence in these critical tools for helping to curb the pandemic.
Here, then, is a rundown of the science that goes into the decision-making process, what it tells us about when results could realistically be available, and when vaccines could start to be administered. This story is based on interviews as well as on documents the drug makers have released detailing their clinical trial plans.
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When will vaccine makers have enough data?
A clinical trial is typically sponsored by a company making a vaccine candidate or an academic institution, or a partnership of both. But it is actually monitored by what is known as a data and safety monitoring board, or DSMB, a group of independent experts hired to make sure volunteers in the study are safe. In many studies, the DSMB has the ability to recommend stopping a study not only if a treatment is unsafe, but also if it is so clearly effective that continuing just wouldn’t be ethical.
In the case of the vaccine trials, the studies being run by Moderna, AstraZeneca, and Johnson & Johnson with the National Institutes of Health share a common DSMB. The study being run by Pfizer and its partner BioNTech has its own.
The DSMBs will conduct what’s called an interim analysis after a certain number of people have been infected with Covid-19 and shown symptoms. Each of these cases is considered an “event,” and each vaccine maker has set a different number of events as a threshold to conduct an interim analysis as part of their trial protocols.
The study being run by Pfizer and its partner BioNTech, frontrunners in the race for a vaccine, is conducting its first interim analysis after 32 events, and would consider the vaccine effective if 26 people in the placebo group and six in its vaccine group had Covid. A study of Moderna’s vaccine, another frontrunner, is waiting until there are 53 cases of Covid.
In the case of Pfizer and BioNTech, an interim analysis could happen in October.
Should a vaccine be approved, potentially for millions of people, after its efficacy has been shown based on 32 cases of Covid-19?
Some experts say no. Eric Topol, the director of the Scripps Research Translational Institute, has been fervently saying that all the trials should continue beyond even their designed ends — when there are about 150 cases of Covid — saying that even the 150 number “may make statistical sense, but it defies common sense.” This could be particularly true if efficacy is limited, given that all the vaccines frequently cause side effects like fever.
Others say that while making a decision based on an interim analysis is fine, the first Pfizer analysis, in particular, seems to set a relatively low bar for efficacy…
Read More: A guide to how — and when — a Covid-19 vaccine could be cleared