Fourth Covid shot provides little benefit against Omicron infection: Study

Afourthdose of existing mRNACovid-19 vaccines may have only "marginal benefits" for younger, healthy adults, according to a new Israelistudypublished Wednesday in the New England Journal of Medicine.

The research assessed 270 health care workers at the Sheba Medical Center in Tel Aviv who received a second boostershotof either the Pfizer or Moderna vaccines, four months after initially getting three Pfizer shots.

Each was age-matchedagainsttwo participants in a control group that had received only three doses of Pfizer, with the median ages in the groups ranging from mid-fifties to early sixties.

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Overall, thefourthshotwas found to be safe, and topped up recipients' neutralizing antibodies -- which block the coronavirus from infecting cells -- to levels comparable to just after the third dose, prior to when antibody levels started waning with time.

Thestudytook place when spread of theOmicronvariant was rife in Israel, and it found that thefourthdose didn't confer much added protectionagainstinfection, despite the reduction over time of antibodies among people who'd received just three shots.

Those who got afourthshotof Pfizer were 30 percent less likely to acquire infection than those who got three doses, while those who got Moderna were 18 percent less likely to get infected.

Thestudyincluded only a small number of participants and was not a randomized trial -- meaning its conclusions should be interpreted with caution -- but the results point towards only minor benefits from the extra dose.

Protectionagainstsymptomatic infection was slightly better in under-40 adult recipients of afourthjab -- 43 percent for Pfizer and 31 percent for Moderna -- compared to people who received three shots.

Thestudyauthors, led by Gili Regev-Yochay, wrote that their research seems to indicate the advantages of three doses of vaccine designedagainstthe original strain of coronavirus had hit a ceiling in terms of immune response, with additional boosters only restoring waned immunity, rather than taking it to new heights.

"Furthermore, we observed low vaccine efficacyagainstinfections in health care workers, as well as relatively high viral loads suggesting that those who were infected were infectious. Thus, afourthvaccination of healthy young health care workers may have only marginal benefits," they said.

Outside experts said the findings showed the need to develop new vaccines.

"IfOmicroncontinues circulating and we are still using the current first-generationCovid-19 vaccinesagainstit, then I agree with the authors that the benefits to otherwise healthy, younger people will be marginal," said Julian Tang, a clinical virologist at the University of Leicester.

"Anyfourthdose boosters will be more beneficial to the older and more vulnerable groups (e.g. those with comorbidities)," he continued.

"Ideally, we need newCOVID-19 vaccines designed specificallyagainstOmicronif we want to improve this protection for the most vulnerable -- in the same way that we update the seasonal flu vaccine each year -- to ensure the best possible matchagainstthe currently circulating virus strain."

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