Many countries are offering a fourth dose of the COVID-19 vaccine to vulnerable populations, but the efficacy of another shot is still in question among some experts and officials.

The Food and Drug Administration has authorized a fourth shot for those 50 and over, as well as those who are immunocompromised.

So, does a fourth dose beef up protection?

A preliminary study suggested that for the general population, the answer could be no.

Published in late February, the study stated that the fourth shot of the Pfizer or Moderna vaccine offered only a little extra protection against the infection compared to three shots.

“Not a third dose, not a fourth dose, not a fifth dose will do anything to stop infections (long term),” said Dr. Gili Regev-Yochay, an infectious disease specialist at Sheba Medical Center in Tel HaShomer, Israel, and lead author of the new study.

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What they’re saying: “What we know from immunology is that if you give another booster, you will see a temporary increase in the neutralizing antibodies. But what we’ve also seen is that these neutralizing antibodies will wane quite rapidly,” the World Health Organization’s chief scientist, Soumya Swaminathan, told CNBC News.

“This happened after the third dose. And it’s happened again after the fourth dose,” she added.

Worth noting: Evidence does suggest that a third dose, or the first booster shot, was crucial for ensuring a generalized immune response against the omicron variant.

State of play: Last month, the Food and Drug Administration convened a panel to devise a plan to explore ways of retooling the coronavirus vaccine so it is effective against newer variants. Clinical trials are underway as the Biden administration tries to create a vaccine strategy for the rest of the year.

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