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What you need to know about the latest news from Pfizer on its COVID-19 vaccine

Under an expected emergency approval, millions of at-risk people could receive it by year’s end.

Pfizer said it expects to produce up to 50 million vaccines this year and up to 1.3 billion doses by the end of 2021.Eva Marie Uzcategui/Bloomberg

Pfizer said Wednesday that its experimental COVID-19 vaccine appeared to be 95 percent effective in warding off the illness that’s surging around the world, a remarkable showing for the first set of complete results from a late-stage clinical trial.

The pharmaceutical giant, which has a large presence in Massachusetts, said it expects to apply to the Food and Drug Administration for the first emergency use authorization of a coronavirus vaccine “within days.”

Here’s a rundown on the latest developments:

Didn’t Pfizer last week say its vaccine was more than 90 percent effective?

Yes, but that was an interim analysis based on 94 confirmed cases of COVID-19 diagnosed among a pool of 43,538 participants. (Half got the vaccine while the other half received placebos.) On Wednesday, Pfizer said it reached 170 confirmed cases, surpassing the required threshold of 164 cases to judge the effectiveness of the two-dose vaccine. Of those 170 cases, 162 were among recipients of a placebo, compared with only 8 eight cases among recipients of the vaccine, which accounts for the 95 percent figure.

Was there other encouraging news from Pfizer?


Yes. The vaccine appeared to be strikingly effective regardless of the age, gender, race, and ethnicity of volunteers. In perhaps the most promising finding, the vaccine appeared to be more than 94 percent effective in people over age 65, who have been among those most likely to become severely ill. “It’s great they highlighted the response in the elderly,” Alan Carr, an analyst at Needham & Co, said in an e-mail to the Globe. “Very reassuring.” There were 10 severe cases diagnosed in the Pfizer trial, and only one occurred in the vaccinated group.

How does all of that compare with the results that Cambridge-based Moderna released for its vaccine on Monday?

They’re very similar. Moderna has been fast on the heels of Pfizer and its German partner, BioNTech. In a late-stage trial of its own, Moderna released interim results based on the first 95 confirmed cases of COVID-19 among volunteers who received two shots of its vaccine. Only five of the 95 people diagnosed with the illness had gotten the vaccine. The other 90 cases occurred in recipients of the placebo. That indicates the Moderna vaccine has an efficacy rate of 94.5 percent. Eleven of the 95 people diagnosed with COVID-19 in Moderna’s snapshot had severe cases of the illness. All 11 occurred in the placebo group. “I expect both vaccines to be in demand,” Carr wrote.


When might people start getting vaccinated?

Dr. Anthony Fauci, the nation’s top infectious disease expert, said Tuesday at the STAT Summit 2020, a virtual event, that as many as 20 million people in US could get coronavirus vaccinations near the end of the year. By then, he said, there could be roughly 25 million doses of vaccine available from Pfizer and 15 million doses from Moderna. The vaccination requires two shots a few weeks apart, so that would mean about 20 million people could get protection — a major step forward, though a sliver of the US population. Pfizer said Wednesday that it expects to “produce globally up to 50 million vaccines” this year ― it gave no breakdown for the US ― and up to 1.3 billion doses by the end of 2021.

What’s next?

Pfizer, which has a plant in Andover that is helping to make the vaccine, plans to request an emergency use authorization shortly. Moderna has said it hopes to do the same “in the coming weeks.” The first vaccines would likely go to people at high risk for catching COVID-19 or suffering severe illnesses, including medical workers, the elderly, and people with underlying conditions. Pfizer chief executive Albert Bourla said Tuesday at the STAT event that the company also has an obligation to provide the vaccine early to people who had participated in clinical trials but received a placebo. “They raised their hands,” he said, referring to their willingness to volunteer for study.


When could everyone else in the United States get one of the vaccines?

That’s hard to say, but certainly not until well into next year. Fauci told CNN’s Jake Tapper on “State of the Union” Sunday that he thinks the US could start getting back to “relative normal” by the spring or summer of 2021, assuming “we get the overwhelming majority of people taking the vaccine.” Public health experts are worried that many Americans will be reluctant to take a vaccine. That’s particularly true of Black Americans, who have suffered a disproportionate share of cases but have been particularly skeptical of a vaccine in public opinion polls. Experts attribute that to unscrupulous medical experiments and procedures performed on Black Americans in the 20th century.

How do the Pfizer and Moderna vaccines work?

Both rely on synthetic messenger RNA, an ingenious variation on the natural substance that directs protein production in cells throughout the body. The vaccines contain custom-made messenger molecules that instruct cells to create a part of the coronavirus and then stimulate the immune system to make antibodies to fend off the disease. If it works ― as the clinical trials indicate ― that would protect people if they ever got infected by the actual virus. No mRNA vaccine has ever been approved.


For how long would the Pfizer and Moderna vaccines provide immunity?

No one knows, but the answer is likely to emerge in coming months. Some experts say it’s possible that booster shots might be needed.

If the FDA ultimately gives full approval to the Pfizer and Moderna vaccines, will those be the only ones needed?

Hardly. There are a dozen coronavirus vaccine candidates in late-stage trials globally that use a variety of approaches, and no company could produce enough of one to protect the world’s 7.8 billion people, regardless of which ones passes muster. The Pfizer and Moderna vaccines have been the only ones to report any results from late-stage trials. Experts are closely following the progress of several other vaccines, including one developed by Johnson & Johnson and Beth Israel Deaconess Medical Center, which uses a different approach and might only require one shot. Interim results from that trial are expected in the coming weeks.

Jonathan Saltzman can be reached at jonathan.saltzman@globe.com.