On November 19, the Food and Drug Administration authorized COVID-19 vaccine boosters for all adults ages 18 and older. The Centers for Disease Control followed suit, recommending that everyone 50 or older should get a booster while those ages 18 to 49 may receive one.

People who received the Pfizer-BioNTech or Moderna messenger RNA (mRNA) vaccine can get a booster six months after their last shot. The CDC had already recommended boosters for those who received the Johnson & Johnson vaccine two months after their first shot. Like the initial shots, the boosters are free, and people can choose any brand of booster; they do not need to get another dose of the vaccine they originally received.

“Booster shots have demonstrated the ability to safely increase people’s protection against infection and severe outcomes and are an important public health tool to strengthen our defenses against the virus as we enter the winter holidays,” CDC director Rpchelle Walensky, MD, MPH, said in a statement. “Based on the compelling evidence, all adults over 18 should now have equitable access to a COVID-19 booster dose.”

A growing body of evidence shows that immunity against SARS-CoV-2, the coronavirus that causes COVID-19, begins to wane a few months after vaccination. But current antibody levels don’t tell the whole story. Antibodies normally decline after infection or vaccination, but memory B cells are left behind to produce more if the virus is encountered again; T cells also provide longer-lasting protection. Circulating antibodies respond immediately and reduce the risk of infection. B-cell and T-cell responses take days to kick in, giving the coronavirus a chance to establish infection, but they can stop it from taking hold in the body and causing serious illness

While the initial two-dose mRNA vaccine series continues to provide good protection against severe illness and death, studies show that vaccine boosters offer additional protection, especially for people over 65. What’s more, boosting antibody levels can help prevent asymptomatic or mild infection and curb transmission, an important consideration at a time when COVID-19 cases are on the rise.

In a highly unusual move, several states and New York City had already gone ahead and opened up booster eligibility to all adults prior to FDA authorization, starting with California on November 9.

“We are taking an expansive approach to COVID-19 boosters, realizing that people are at risk of getting COVID or spreading it as we enter the busy holiday season,” said San Francisco Director of Health Grant Colfax, MD. “We have been stressing that boosters are essential for higher risk individuals, but now it’s become apparent that we need many more people to receive a booster dose so that we can protect ourselves, our families and friends and our community.”

On August 12, the FDA authorized and the CDC recommended an additional dose of the Pfizer-BioNTech and Moderna vaccines for immunocompromised people, including organ transplant recipients, people being treated for cancer and people with advanced or untreated HIV. Health officials make a distinction between an additional doses needed to achieve full protection for people with a poor initial response and a booster intended to shore up waning immunity in those who had a good initial response. The expanded recommendation means caregivers and household members of immunocompromised people can get boosters to help protect this vulnerable group.

 

In September and October, the FDA and CDC went further, recommending Pfizer-BioNTech and Moderna boosters after six months for people 65 and older, younger adults with underlying health conditions and those at high risk for exposure due to their work or living situation. The agencies also said all adults who received the J&J vaccine could get an additional shot after two months. Immunocompromised people who received an additional dose to complete their initial vaccine series can also get a booster six months later, for a total of four shots.

At that time, the FDA and CDC did not go so far as to make all adults eligible for boosters, throwing a wrench into the Biden administration’s universal booster plan announced in September. But a resurgence of COVID-19 cases in many parts of the country as well as growing evidence of waning immunity and the benefits of boosters led the agencies to reverse their earlier decisions.


Experts say it’s not yet clear whether a third vaccine dose will lead to more durable protection or whether additional boosters will be needed on a regular basis going forward. Some think that a three-dose mRNA vaccine series, with the first two shots given three or four weeks apart and the third several months later, could provide long-lasting immunity, but only time will tell.

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