Who Should Receive Covid-19 Vaccine Boosters?

Now that a majority of Americans have received their initial COVID-19 vaccines, attention has turned to boosters. Two main factors determine whether additional doses are needed: Do the original vaccines still work against current SARS-CoV-2 variants? Does immunity wane over time?

The three vaccines authorized in the United States, from Pfizer-BioNTech, Moderna and Johnson & Johnson, remain active against the predominant Delta variant. However, while they still provide good protection against severe disease, hospitalization and death, they are less effective at preventing infection.

Immunity against SARS-CoV-2, either after infection or vaccination, does wane over time. But while antibody levels begin to decline after a few months, memory B cells are left behind to produce more antibodies if the virus is encountered again. T cells also play a role in fighting SARS-CoV-2.

In August 2021, the Food and Drug Administration (FDA) authorized and the Centers for Disease Control and Prevention (CDC) recommended an additional Pfizer-BioNTech or Moderna vaccine dose for immunocompromised people, including organ transplant recipients, people being treated for cancer and those with advanced or untreated HIV. Some people with suppressed immune function do not produce enough antibodies after the first two doses. For some, a third dose does the trick, but others are still not fully protected.

The FDA and CDC later went further, recommending Pfizer-BioNTech and Moderna boosters for people ages 65 and older, younger adults with underlying health conditions and those at high risk for exposure due to their work or living situation as well as for anyone who received the J&J vaccine. Finally, on November 19, the agencies recommended boosters for all adults six months after the last Pfizer or Moderna shot or two months after the J&J shot. People do not need to get the same vaccine brand as a booster.

Experts disagree about whether most healthy younger adults need boosters. An additional vaccine dose raises antibody levels and reduces hospitalization in older people, but protection against severe disease seems to be holding up well for younger people after two doses. On a public health level, boosters can help curb transmission, but the increase in antibodies after a booster may also last only a few months.

It is not yet clear whether people will need boosters every year or even every six months. Some experts think that because the initial Pfizer-BioNTech and Moderna shots are given so close together (three or four weeks, respectively), a third dose with longer spacing could lead to stronger immunity and frequent boosters won’t be necessary.

New types of COVID-19 vaccines may be an option in the future. Current boosters are an extra dose of the same vaccines, but researchers are working on new vaccines tailored to the Delta variant and others that would work against multiple variants or different coronaviruses. Scientists are also testing nasal vaccines, which produce antibodies in the nose, in the hope that they will better prevent infection and transmission.


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