Unvaxed people should expect to get COVID-19 every 16 months

Annual flu shot drives have shown that age can dampen the effectiveness of some vaccines. Verdin says a third of people over age 70 don’t respond at all to the flu vaccine, which is why it still kills a disproportionate number of older Americans every year.

On the other hand, responses to COVID-19 vaccines have been a lot stronger. “I think one of the more surprising things is how well the mRNA vaccines did with those older populations,” Bhattacharya says. “If you look at the initial immune responses, they weren’t very much different at all between people over 65 and those below. So that was a pretty pleasant surprise.”

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And despite the drop in effectiveness in preventing infection, the Pfizer vaccine remains 90 percent effective at preventing hospitalization, which shows that it remains a solid defense against severe disease and death. A recent report published by the U.S. Department of Health and Human Services said that vaccines “may have helped prevent hundreds of thousands of new COVID-19 infections and tens of thousands of deaths among seniors.”

Bhattacharya says that federal regulators in the U.S. have approved boosters for people over 65—and not the general population—because of the extra risks that they face. He and other scientists emphasize that high-profile breakthrough infections and the approval of booster shots should not discourage anyone from getting vaccinated. On the contrary, it should be seen as confirmation that the vaccines work.

“Rest assured, these are the best vaccines we’ve ever had,” Petri says.

Verdin agrees: “Getting vaccinated really puts things on your side. Think about it as a war where you want to have all the ammunition that you can possibly have.”