What does efficacy mean with vaccines?

You may have seen the numbers: The COVID-19 vaccines have a 95 percent efficacy rate.

But what you may not know is that 95 percent efficacy does not mean that five percent of vaccinated people will still get COVID. According to Live Science, the actual percentage of vaccinated people who still got COVID-19 was a hundred times less than five percent: Just .04 percent. (Pfizer and Moderna trials). This means that the vaccines are highly effective in preventing the worst outcomes of COVID-19.

The 95 percent efficacy rate means that vaccinated people had a 95 percent lower risk of getting COVID-19 symptoms compared with individuals in the control group, who didn’t get vaccinated at all.

As a matter of fact, the vaccines were all 100 percent effective in preventing severe disease (hospitalization and death) within six weeks after the first dose (Moderna) or seven weeks (Pfizer and Johnson & Johnson).

Zero vaccinated people in any trial were hospitalized or died of COVID-19 after the vaccines had fully taken effect.

Every vaccine trial looked at protection from experiencing symptoms, not protection from getting infected at all. Although it is possible that the vaccines also reduce the number of viral particles in the body — which would cut transmission — scientists are not yet sure if vaccinated people can still transmit the virus. That’s why people should still wear masks.