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Is it time to consider a second COVID vaccine booster? Health experts say it’s premature.

They cite the need to distribute first doses to parts of the world, along with the challenges of convincing vaccinated people to get yet another shot.

A COVID-19 booster was administered earlier this month in Oakland, Pa.Andrew Rush/Associated Press

As Omicron infections surged a month ago, Israel began offering fourth doses of COVID-19 vaccines to older and immunocompromised people and to health care workers in an effort to shield them from what was deemed the most transmissible strain yet of the coronavirus.

But health experts say it’s premature for the United States to take similar steps, at least for the foreseeable future. They cited the falling rate of Omicron cases, the exposure of most Americans to the SARS-CoV-2 virus through vaccinations or infections, and growing evidence that two shots and a booster already provide remarkably strong protection from severe illness and death.

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Not to mention that giving multiple booster shots each year may not be sustainable.

“Boosting every three to six months is probably not a feasible strategy in the developed world and probably not even possible in the developing world,” said Dr. Dan Barouch, who runs the Center for Virology and Vaccine Research at Beth Israel Deaconess Medical Center.

Barely 15 percent of the population of Africa has received at least one dose of a COVID vaccine as a result of production woes, export bans, and vaccine hoarding by rich nations. With so many people still unvaccinated in swaths of the world, Barouch said, administering primary shots remains a far bigger priority than boosters.

Barouch’s laboratory helped create the Johnson & Johnson vaccine and has studied the more popular rival shots from Pfizer-BioNTech and Moderna. Although he acknowledged that boosters have their place, he said vaccinating the unvaccinated is crucial to warding off severe illness and preventing other variants from emerging.

The lukewarm interest in the first booster shots also suggests that follow-ups would have even less appeal. Only about 41 percent of Americans eligible to receive boosters have gotten one, according to the US Centers for Disease Control and Prevention. Overall, a little more than a quarter of the US population is fully vaccinated and boosted.

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“The enthusiasm for boosters is not as high as the initial enthusiasm for vaccines,” Barouch said. “With calls for third, fourth, and fifth shots, public enthusiasm is likely to go down with each recommended booster.”

Israel was the first country to fully vaccinate a majority of its citizens against COVID and has often been a bellwether in the pandemic. In early January, the country began offering booster shots to its most vulnerable citizens, including people over 60.

On Jan. 23, the Israeli Health Ministry released data showing that a fourth dose of a COVID vaccine given to those over age 60 made them three times more resistant to serious illness than recipients of three shots in the same age group. The fourth dose, or second booster, also made people over 60 twice as resistant to infection, although a preliminary study published by Israel’s Sheba Medical Center indicated that the heightened antibody levels probably aren’t enough to completely ward off Omicron.

Nonetheless, health specialists say there’s no compelling reason for the United States to follow Israel’s lead, at least for now.

For one thing, Omicron cases are on the decline, particularly in the Northeast and the Midwest, although cases are climbing in areas like the Rocky Mountain states. The spread of an Omicron subvariant that appears to be even more contagious has some experts warning that it could take longer than expected for the latest surge to completely wane. Nonetheless, Dr. Scott Gottlieb, former director of the US Food and Drug Administration, said Sunday that he didn’t expect “a huge wave of infection” and predicted that “the decline will happen nonetheless.

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In addition, although Omicron substantially reduces the levels of disease-fighting antibodies in blood taken from inoculated people, other components of the immune system, including T cells, continue to provide robust protection. Two shots of Pfizer’s vaccine or one shot of J&J’s vaccine gave durable T cell responses for at least eight months without a booster, according to a study by Barouch’s lab published in Nature on Monday.

Several scientists also say that the highly contagious Omicron variant has infected so many people since it was first reported in November in Africa that it could mark COVID’s transition from a pandemic to an endemic disease and make a fourth shot unnecessary.

“Hopefully, Omicron has given us a lot of immunity,” said Dr. Monica Gandhi, an infectious diseases doctor at the University of California, San Francisco, who thinks that people in the United States might not need a fourth shot unless they are immunocompromised.

Gandhi acknowledged that COVID has proven prognosticators wrong again and again. The situation could change, she said, if another highly contagious variant emerges, particularly one that that causes more severe symptoms than Omicron, which generally turned out to be milder than earlier strains, especially in fully vaccinated people.

But she is optimistic that COVID could be turning into a more manageable disease.

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“This is what happened with the [influenza] pandemic in 1918,” she said. “It did end. It didn’t mean influenza went away but [the pandemic] did end.”

On Jan. 13, the Institute for Health Metrics and Evaluation at the University of Washington said it expects Omicron to continue to circulate and possibly flare up later this year as immunity wanes. The institute predicted that new variants will emerge this year and COVID will remain a health problem. But, it added, “the notion of a pandemic requiring extraordinary intervention and behavioral change is likely over by early March.”

After that, the institute said, COVID could be controlled with measures like antiviral medications and mask use by the vulnerable “if and when another wave occurs.”

The makers of the three COVID vaccines cleared by the Food and Drug Administration, Pfizer, J&J, and Cambridge-based Moderna, have developed Omicron-specific booster shots. Pfizer and Moderna, whose vaccines rely on messenger RNA, have begun testing them in clinical trials. J&J, whose vaccine uses a viral vector, plans to do so as well. Preliminary results are expected within several months.

Dr. Walter A. Orenstein, a professor of medicine at Emory University and associate director of the Emory Vaccine Center, said that he believes a variant-specific booster will probably ward off Omicron infections better than existing boosters, which, like the original vaccines, are based on the virus that emerged in Wuhan, China, in December 2019.

But with the declining number of Omicron cases, he hopes that a variant-specific booster won’t prove necessary.

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“It’s better to have them and not need them than to need them and not have them,” he said. “If it turns out we don’t need it, we’ve gotten some insurance.”


Jonathan Saltzman can be reached at jonathan.saltzman@globe.com.