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Fourth COVID shot provides little benefit against Omicron infection: study
The research assessed 270 health care workers at the Sheba Medical Center in Tel Aviv who received a second booster shot of either the Pfizer or Moderna vaccines, four months after initially getting three Pfizer shots.
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A health worker prepare to give the Pfizer COVID-19 coronavirus vaccine at a makeshift clinic at the Aceh Museum in Banda Aceh on Jan. 17, 2022. (AFP/Chaideer Mahyuddin)
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fourth dose of existing mRNA Covid-19 vaccines may have only "marginal benefits" for younger, healthy adults, according to a new Israeli study published 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 booster shot of either the Pfizer or Moderna vaccines, four months after initially getting three Pfizer shots.
Each was age-matched against two 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.
Overall, the fourth shot was 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.
The study took place when spread of the Omicron variant was rife in Israel, and it found that the fourth dose didn't confer much added protection against infection, despite the reduction over time of antibodies among people who'd received just three shots.
Those who got a fourth shot of 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.
The study included 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.
