A fourth dose of the mRNA vaccines did not provide better protection against COVID-19 transmission than vaccination with three doses, researchers said in a new study.

Efficacy Of A Fourth Dose

In a study published in The New England Journal of Medicine Wednesday, scientists reported their findings after examining the efficacy of the fourth dose of the mRNA coronavirus vaccines from Pfizer and Moderna. According to the researchers from Sheba Medical Center, the fourth dose offered little to no protection against the transmission of SARS-CoV-2.

For the study, the team examined 1,050 eligible health care workers enrolled in the Sheba cohort. Of the total number, 154 received a fourth dose of the Pfizer vaccine, while 120 got jabbed with a fourth Moderna vaccine a week later. For each participant, two age-matched controls were selected from the remaining eligible health care workers.

Both vaccines induced IgG antibodies against severe COVID-19 and increased neutralizing antibody titers. Meanwhile, antibody levels in the controls continued to wane. Interestingly, the researchers found that the fourth dose of the vaccines did not necessarily lead to substantial protection against the virus compared to three doses of the mRNA vaccines.

Vaccine efficacy against SARS-CoV-2 infection was 30% for Pfizer’s fourth dose and 11% for Moderna’s. It should be noted that 18.3% of the participants in the Pfizer group contracted omicron, while 20.7% in the Moderna group were infected with the same variant. As for the control group, 25.0% caught the omicron strain.

Even though the fourth dose offered little to no protection against coronavirus transmission, it did provide moderate protection against symptomatic infection among young and healthy individuals jabbed with three doses of the mRNA vaccines.

“We found no differences, both in terms of IgG antibody levels and in terms of neutralizing antibody levels, which reached a level similar to that measured a month after the third dose was administered,” Prof. Gili Regev-Yochay, director of the Infection Prevention and Control Unit at Sheba and head researcher of the study, told The Jerusalem Post.

Do We Need A Fourth Dose?

There has been an ongoing debate on the possible need for a fourth dose as the pandemic continues to its second year. The interim findings of the study showed that a fourth dose did not provide better protection than the first three doses, but it would play an important role in the fight against the novel coronavirus in the long run.

Regev-Yochay pointed out that the fourth dose would be needed for populations with risk factors, so they would be protected from the serious form of COVID-19. The findings also help provide a scientific basis for better management of the pandemic.

Last weekend, Pfizer CEO Albert Bourla told CBS “Face The Nation” that the fourth dose would be necessary for people to stay protected longer. Since the immunity provided by the vaccines tends to wane after some time, getting another shot would help extend the protection from the virus.

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