A fourth dose of existing Covid-19 mRNA vaccines may only have “marginal benefits” for young and healthy adults, according to a new Israeli study published in the New England Journal of Medicine on Wednesday.
The study evaluated 270 health workers at Tel Aviv’s Sheba Medical Center, who received a second dose booster of Pfizer or Moderna vaccines, initially receiving three shots from Pfizer and four months later.
Each was paired against two participants in a control group with only three doses of Pfizer, with a median age of groups ranging from the mid-fifties to the early sixties.
Overall, the fourth shot was seen to be safe, and the recipient’s neutralizing antibodies – which block coronaviruses from infecting cells – rose to levels equal to the third dose before antibody levels began to decline over time.
The study was conducted in Israel when the spread of the Omicron variant was abundant, and found that the fourth dose did not provide much protection against infections, although antibodies were reduced over time among people who had only three shots.
Those who received a fourth shot of Pfizer were 30 percent less likely to catch the infection than those who received three doses, while those who received Moderna were 18 percent less likely to become infected.
The study included only a small number of participants and was not a randomized trial, i.e. its effects should be interpreted with caution, but the results show only minor benefits of the additional dose.
The protection against symptomatic infection was slightly better in recipients of adults under the age of 40 who had received a third shot – 43% for Pfizer and 31% for Moderna – compared to those who received three shots.
The authors of the study, led by Gili Regev-Yochay, wrote that their research indicates that the benefits of three vaccines designed against the original strain of coronavirus hit the ceiling in terms of immune response, with additional promoters restoring only weakened immunity. instead of moving to new heights.
“We have also seen the low efficacy of the vaccine against infections in health care workers, as well as the relatively high viral load, which suggests that those infected were infectious. So the fourth vaccine for healthy young health care workers has only marginal benefits,” they said. he said.
External experts said the findings showed the need to develop new vaccines.
“If Omicron continues to circulate and we are still using the current first-generation Covid-19 vaccine against it, then I agree with the authors that otherwise the benefits for the healthiest and youngest will be marginalized,” said Julian Tang, a clinical virologist. University of Leicester.
“The fourth dose booster will be more beneficial for older and weaker groups (e.g., those with comorbidities),” he continued.
“Ideally, we need new COVID-19 vaccines specifically designed against Omicron if we want to improve this protection for the most vulnerable – in the same way we update the seasonal flu vaccine every year – to ensure the best possible match. The strain of the virus is currently circulating.”
(This story was not edited by NDTV staff and was automatically created from a union feed.)