Efficency ofCovid vaccines fades over time, prompting some debate over boosters

What We Know So Far About Waning Vaccine Effectiveness Vaccines still offer strong protection against severe Covid-19, but many studies show their protection against infection decreases over time. How much that decline matters is up for debate. The New York Times

As tens of millions who are eligible in the United States consider signing up for a Covid-19 booster shot, a growing body of early global research shows that the vaccines authorized in the United States remain highly protective against the disease’s worst outcomes over time, with some exceptions among older people and those with weakened immune systems.

But while the vaccines’ effectiveness against severe disease and hospitalization has mostly held steady, even through the summer surge of the highly transmissible Delta variant, a number of published studies show that their protection against infection, with or without symptoms, has fallen.

Public health experts say this decline does not mean that the vaccines are not working.

In fact, many studies show that the vaccines remain more than 50 percent effective at preventing infection, the level that all Covid vaccines had to meet or exceed to be authorized by the Food and Drug Administration back in 2020. But the significance of these declines in effectiveness — and whether they suggest all adults should be eligible for a booster shot — is still up for debate.

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A study in England examined the vaccines’ effectiveness against the Delta variant over time. It found that the Pfizer-BioNTech vaccine is about 90 percent effective at preventing symptomatic infection two weeks after the second dose but drops to 70 percent effective after five months.

The same study found that the Moderna vaccine’s protection also drops over time.

A study in the U.S. and another in Canada looked at the vaccines’ effectiveness at preventing any infection from Delta, symptomatic or not. Although they found different levels of decline, both studies found that the vaccines’ protection dropped over time.

But both the English and Canadian studies found that even after several months, the Pfizer-BioNTech and Moderna vaccines remain highly effective at preventing hospitalization. ...

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experts have been divided over whether booster shots are necessary for those beyond the most vulnerable.

There has been more agreement among experts about the need to offer extra protection to adults over 65. The declines observed in vaccine effectiveness for this age group may have greater repercussions, since older people face a higher risk of hospitalization from Covid. ...