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COVID-19 vaccines testing timeline: What’s ahead after Pfizer’s surprising good news

When coronavirus vaccines will be ready for us to roll up our sleeves for a shot depends on a long list of research steps. Here’s how it all works and what to expect.

Pfizer says an early peek at its vaccine data suggests the vaccine shots it’s developing might be 90% effective at preventing COVID-19, but that doesn’t mean a coronavirus vaccine is imminent.
Pfizer says an early peek at its vaccine data suggests the vaccine shots it’s developing might be 90% effective at preventing COVID-19, but that doesn’t mean a coronavirus vaccine is imminent.
Bebeto Matthews / AP

Now that drugmaker Pfizer Inc. has announced its surprising good news that its COVID-19 vaccine might offer more protection than anticipated, what’s next?

Pfizer and the maker of the other leading U.S. vaccine candidate, Moderna Inc., have been cautioning that the earliest they could seek regulatory approval for wider use of their shots would be late November. In Britain, AstraZeneca recently said it hoped to prove its vaccine is effective by year’s end.

Science moves at its own pace. While COVID-19 vaccines are being developed at record speeds, when they’ll be ready for us to roll up our sleeves for a shot depends on a long list of research steps, including how many study volunteers wind up getting the coronavirus.

Here’s a look at the process to better understand what to expect:


Pfizer and its German partner BioNTech enrolled nearly 44,000 people in final testing of their vaccine. Participants, their doctors and Pfizer all are kept in the dark about who gets the real vaccine and who gets a dummy shot, or placebo. They get a second dose about three weeks after the first.

A week after the second dose, key tracking begins: counting anyone who experiences COVID-19 symptoms and tests positive for the virus as participants go about their daily routines.

Late-stage testing of other vaccine candidates is similar, varying slightly in the number of volunteers and timing.


Every vaccine study is overseen by an independent “data and safety monitoring board,” or DSMB. These boards include scientists and statisticians with no ties to the vaccine makers.

Before a study is finished, only the DSMB can unlock the code that shows who got real vaccine and who got a placebo and recommend whether the shots are working well enough to stop testing early.

Those boards take sneak peeks at predetermined times agreed to by the manufacturer and the federal Food and Drug Administration. The first interim analysis for Pfizer came Nov. 8, when the company reported its data monitors had counted 94 infections so far — and that, among those initial cases, the vaccine appeared to have been a remarkable 90% effective, far better than experts expected.

But the study isn’t stopping. To be sure about how much protection the vaccine might offer, the study is set to run until there are 164 infections. The more COVID-19 cases that occur in the trial, the better an idea scientists will have of just how protective the shots really are.


Pfizer’s initial plans called for evaluating when just 32 infections had been counted. But many scientists warned that was too small a sampling from which to draw any reliable conclusions about a vaccine that’s needed by billions of people worldwide.

Pfizer said it reconsidered, going back to the FDA for permission to change the plan and do its first interim analysis when there were more cases. By the time Pfizer made the change and caught up with a backlog of virus tests, the DSMB had 94 infections to analyze.

The higher number increases confidence in those still preliminary results, said Dr. Jesse Goodman, a former FDA vaccine scientist now at Georgetown University.

Moderna, AstraZeneca and other companies that aren’t quite as far along in their final testing all have set slightly different timelines for when their data monitors will peek at how the shots are working.


Safety is the top priority. Monitors watch for unexpected or serious side effects. Earlier this fall, studies of vaccine candidates made by AstraZeneca and Johnson & Johnson were temporarily halted after some participants experienced health problems, delaying the research until safety investigations allowed both to resume.

Pfizer says no serious safety concerns have emerged so far with its vaccine.

But the FDA is requiring that companies track at least half of study volunteers for two months to look for side effects before asking the agency to review their vaccine. That’s about when side effects have cropped in studies of other vaccines.

Pfizer and Moderna both expect to reach that safety milestone later in November.


Companies are expected to seek permission for “emergency use” of their vaccines, rather than waiting to fully complete their studies and then seeking traditional approval.

The FDA’s scientific advisers then will debate each company’s study findings at a public meeting before the agency decides.

Manufacturers already have begun stockpiling vaccine doses in anticipation of eventual approval.

Still, the first shots will be in short supply and rationed.

And the first people vaccinated will need to undergo extra safety tracking, as the government watches for rare side effects that might crop up when the shots are given to many more people than were involved in the research studies.