The authors of the study, led by Gili Regev-Yochay, wrote that the research suggests that the benefits of the three vaccine doses designed against the original strain of coronavirus peak in terms of immune response.
Additionally, additional boosts only restored diminished immunity, rather than taking it to new heights.
“We observed low vaccine efficacy against infections in healthcare workers, as well as relatively high viral loads that suggested those infected were infectious. Therefore, a fourth vaccination of healthy young healthcare workers may only have marginal benefits,” they pointed out.
The research, published in the New England Journal of Medicine, evaluated 270 healthcare workers at Sheba Medical Center in Tel Aviv who received a second booster dose of Pfizer or Moderna vaccines four months after receiving three Pfizer vaccines.
The age of each was compared to that of two participants in a control group who received only three doses of Pfizer, with the average age of the groups ranging from 50 to 60 years old.
Overall, the fourth injection was found to be safe and increased receptor-neutralizing antibodies – which prevent the coronavirus from infecting cells – to levels comparable to those just after the third dose, before levels of antibodies do start to decline over time. .
Those who received a fourth dose of Pfizer were 30% less likely to be infected than those who received three doses, while those who received Moderna were 18% less likely.