New Pfizer results show its COVID-19 vaccine is nearly 95% effective

Skyrocketing infections sped up the final analysis of data from the Phase III trial

photo of a syringe with the Pfizer and BioNTech logos in the background

A COVID-19 vaccine developed by global pharmaceutical company Pfizer and German biotech company BioNTech is highly effective at preventing people from getting sick, new results show.

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Pfizer’s coronavirus vaccine candidate may be more effective than early results suggested.

Just a week after releasing interim results suggesting the vaccine was more than 90 percent effective (SN: 11/9/20), the pharmaceutical giant and its German biotech partner BioNTech announced final results of their 41,000-person clinical trial. A final analysis indicates that the vaccine is safe and 95 percent effective at preventing illness, the companies announced November 18. The results, shared in a news release, have yet to be peer reviewed by other scientists.

Final results depended on getting a certain number of infections in the study group. Normally it might take months to tally the cases needed to make a final efficacy determination, but infection rates in the United States have been so high that coronavirus cases quickly racked up in the trial, speeding up the timeline for analyzing the final results. 

Among 170 volunteers who contracted COVID-19, 162 had gotten a placebo. Just eight cases were recorded in the group that received the vaccine. 

Efficacy of Pfizer’s vaccine is comparable to preliminary results from Moderna’s vaccine trial, announced November 16 (SN: 11/16/20). Both vaccines use messenger RNA, or mRNA, to carry instructions for making the coronavirus’ spike protein to human cells. Human cells read those instructions and produce the viral protein, priming the immune system to ward off the virus should it be encountered later.

The vaccine, which requires two shots spaced a month apart, may also lessen severity of the disease. During the trial 10 people became severely ill. Nine of those people were in the placebo group, while one severely ill person was in the vaccine group. Among people 65 and older, the vaccine was more than 94 percent effective, the companies said. That’s particularly good news because vaccines often are not as effective in older people, because immune systems tend to weaken with age.

Pfizer and BioNTech plan to apply to the U.S. Food and Drug Administration for an emergency use authorization within days, and say 50 million doses of the vaccine — enough to immunize roughly 25 million people — will be available by the end of the year. 

The news comes as COVID-19 cases continue to skyrocket. As of November 18, nearly 58 million people globally have been infected and 1.3 million people have died, according to Johns Hopkins University’s COVID-19 tracker. The United States leads the world in cases, with 11.4 million infections and nearly 249,000 deaths. More than 100,000 new cases and about 1,500 deaths are being recorded nationwide every day, and many states are tightening or implementing new public health measures to counter the virus’s spread.

Tina Hesman Saey is the senior staff writer and reports on molecular biology. She has a Ph.D. in molecular genetics from Washington University in St. Louis and a master’s degree in science journalism from Boston University.

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