A second booster dose of current messenger RNA vaccines may have only “marginal benefit” against COVID-19 infections in healthy young adults, according to an Israeli study published Wednesday by the New England Journal of Medical.
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The study covers approximately 600 healthcare workers at Sheba Medical Center, 270 of whom received a second booster of either Pfizer or Moderna serums four months after receiving their third dose. The rest received only three doses of Pfizer.
In general, the fourth dose is safe and brings the level of neutralizing antibodies, which block the infection of cells by the coronavirus, to its level after the third dose.
The study, which took place when the Omicron variant was circulating widely in Israel, however, suggests that the fourth dose provides little additional protection against infection despite the gradual decline in antibody levels for those who received three. doses.
The fourth dose of Pfizer lowers the risk of being infected with COVID-19 by 30% compared to three doses and that of Moderna lowers these chances by 18%.
Protection against symptomatic forms of the disease is slightly better than for those who received three doses: 43% with Pfizer and 31% with Moderna.
These results suggest minor benefits, but they should be taken with caution, given the small number of participants.
According to their authors, led by Professor Gili Regev-Yochay, the study seems to indicate that the three doses of vaccines developed against the original form of COVID-19 have reached a ceiling in terms of immune response and that boosters are only restore this immunity without increasing it.
“In addition, we observed low vaccine efficacy against infections among healthcare workers and a relatively high viral load suggesting that infected patients were contaminating. So a fourth dose might only have marginal benefit” for them.
Experts outside the study felt that this study showed the need to develop new vaccines.
“If Omicron continues to circulate and we still use the first generation vaccines, I agree with the conclusions of the authors” for young healthy adults, commented Julian Tang, virologist at the University of Leicester.
“A fourth dose will be more beneficial to the elderly and more vulnerable groups” such as those with comorbidities, he added.
“Ideally, we need new COVID vaccines developed specifically against Omicron if we want to improve protection for the most vulnerable, like when we develop the flu vaccine every year,” he said.
The Pfizer-BioNTech alliance announced on Tuesday that it has asked the United States Medicines Agency to authorize a second booster dose of their vaccine against COVID-19 in people 65 years of age and older.