Pfizer claims its COVID vaccine is 90 percent effective. Here’s what that actually means.

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A 90 percent effectiveness is very impressive, but the rate is based on a relatively small number of people. Pixabay

(Claire Maldarelli/ Popular Science) — On Monday, pharmaceutical company Pfizer announced the latest results for their coronavirus vaccine, which is now in late-stage clinical trials. The results, which were evaluated by an independent committee of experts (though not yet peer-reviewed), show that based on the information they have thus far, the drug is at least 90 percent effective in preventing COVID-19 among participants who had not previously been infected with the novel coronavirus.

These results are promising, and are coming at a time when the world is anxiously awaiting positive news. However, there’s still a long way to go before researchers can be certain that this vaccine is indeed as effective as it seems.

“The results are really quite good, I mean extraordinary,” Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases, told The Washington Post.

Other outside experts expressed similar cautious optimism. “We need to see the actual data, and we’re going to need longer-term results,” Jesse Goodman, a professor of medicine and infectious diseases at Georgetown University, told The New York Times. Adding, “it’s a testament to hard work and science that we’re getting results that are so good and so fast.” (…)

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