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Here's how health experts know the COVID-19 vaccine works

2 Wants To Know digs into the study behind Pfizer's new vaccine.
Credit: Getty Images
COVID-19 Vaccine

GREENSBORO, N.C. — Last year the flu shot you got was only 45 percent effective, so healthcare workers say for a coronavirus vaccine to be 95 percent effective is a big deal. But how does the drug company know that?

Pfizer said it enrolled 44,000 people in a study. They split the group into two. Half got the vaccine. The other half got a fake shot full of saltwater. After getting the shots, 170 people in the study caught coronavirus. 162 of them were in the fake shot group. And eight came from people who had the vaccine. The vaccine reduced the risk of catching the virus by 95 percent.


That's what we know, but there is still a big question: how long will you be protected?


The study also revealed possible side effects. Out of the group that got the real vaccine, Pfizer says 3.8 percent felt severe fatigue and 2 percent a severe headache. And people in the trial reported something else right after they took the shot, a spike in fever. But the side-effects appear to be temporary and Governor Roy Cooper says he has confidence the vaccine is safe.

"When the time comes, I'll be ready to roll up my sleeve," Cooper said.

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