COVID boosters are back: what scientists say about whether to get one

Across the Northern Hemisphere, public-health officials are rushing to roll out autumn COVID-19 vaccination campaigns to guard against a fresh batch of SARS-CoV-2 variants. In England, officials moved the start date for administering an updated booster to Monday — roughly a month earlier than planned. The US Centers for Disease Control and Prevention (CDC) on Tuesday recommended newly formulated boosters to all people above the age of six months.

But many nations are recommending the top-up jabs only for those at elevated risk of hospitalization or death, such as people aged 60 and above. Where does that leave the millions of people who fall outside those high-risk groups?

Scientists say that younger people who are healthy and already vaccinated will still have some protection against severe disease if they sit out the new round of jabs. But researchers also say that even for individuals outside the high-risk groups, another booster will reduce the risk of a new SARS-CoV-2 infection — although fleetingly — and offers additional advantages as well.

“Anyone who takes it will benefit,” says immunologist Rafi Ahmed at Emory University in Atlanta, Georgia.

Booster bonanza

Some nations have repeatedly offered booster doses in the past few years. In the United States, for example, boosters have been rolled out at least twice for low-risk individuals and four times for high-risk people since 2021.

But the booster calculus has changed, because so many people have been exposed to SARS-CoV-2 one way or another. In England, for example, more than three-quarters of the population had been vaccinated, infected or both by mid-February. In Beijing, more than 90% of people had been infected by the end of January¹.

Now many countries no longer have a boosters-for-all policy (see ‘Another autumn, another COVID booster’). Health officials in the United Kingdom announced in August that autumn boosters would be offered only to the most vulnerable individuals, such as adults aged 65 and over and health care workers. France does not recommend an autumn booster for people outside vulnerable groups. Germany is not mounting an autumn booster campaign at all, although it does advise an annual booster for people in high-risk groups.

Among the outliers is the United States. On Tuesday, independent scientists who provide advice to the CDC voted 13 to 1 to recommend universal access to the updated vaccine.

Benefits from the updated booster “are anticipated in all age groups,” said CDC epidemiologist Megan Wallace before the vote. Models predict that more hospitalizations and deaths are avoided when universal access is provided than if the booster were recommended only to people aged 65 years and older, she said.

Researchers generally agree that, because the boosters’ main effect is preventing severe disease, high-risk individuals are the ones who benefit most from another jab. “For the elderly, the immunosuppressed and people with comorbidities, it makes a lot of sense to get the booster, and they probably need more than one every year,” says immunologist Dan Barouch at Beth Israel Deaconess Medical Center in Boston, Massachusetts.

The shift away from universal boosters, however, leaves people outside vulnerable groups to decide for themselves — and scientists are divided.

To boost or not to boost

For low-risk individuals, the booster “is not necessarily protecting them against severe disease because they don’t have that risk to begin with,” says Amesh Adalja, an infectious disease specialist at the Johns Hopkins Center for Health Security in Baltimore, Maryland.

But he and others say that boosters can delay SARS-CoV-2 infection in low-risk people, although the vaccination won’t block infection indefinitely. Boosters can also shorten a bout of COVID-19, Ahmed says, which might lead to a reduction in viral transmission.

Why a highly mutated coronavirus variant has scientists on alert

Epidemiologist Michael Osterholm at the University of Minnesota in Minneapolis says that low-risk individuals should be able to choose to get a vaccine. He cites a recent increase in the number of COVID-19 hospitalizations among young US children to argue that parents might be justified in wanting to vaccinate their child. But he also agrees that it’s okay for healthy individuals to skip this booster. Barouch says that ”there is controversy” among experts about whether younger, low-risk people should get it.

Another complicating factor is the rise of new SARS-CoV-2 variants, such as the highly mutated Omicron descendant BA.2.86. Its appearance prompted health officials in England to accelerate the rollout of autumn boosters, among them an updated version targeting the Omicron offshoot called XBB.1.5, which prevailed in many countries in the first half of 2022. The vaccines recommended in the United States also target XBB.1.5.

Reassuring results

Recent data suggest that despite earlier worries about its efficacy, the updated booster is likely to be effective against BA.2.86 and its competitor variants. Moderna announced last week that its vaccine targeting XBB.1.5 generates antibodies against BA.2.86 and other variants in circulation. According to a study² published 4 September on the preprint server bioRxiv, antibodies from people infected with SARS-CoV-2 when XBB.1.5 was in circulation are active against BA.2.86. The study has not yet been peer reviewed.

Barouch’s team evaluated people who had been infected with the XBB variant and found³ that their antibody responses to all the variants, including BA.2.86, increased after infection. “This suggests that the vaccine based on XBB.1.5 … should be able to raise antibody responses against all circulating variants,” Barouch says. The work, published 5 September on bioRxiv, has not yet been peer reviewed.