A study published in the New England Journal of Medicine revealed that a fourth dose of the Pfizer-BioNTech vaccine lowered the rates of confirmed Omicron-related COVID infection and severe disease.

The trial enrolled 1,252,331 adults from Israel, aged 60 and up who were eligible for the fourth dose during the Omicron wave.  623,355 people received the fourth dosage, whereas 628,976 people did not. The rates were calculated using the quasi-Poisson regression approach.

In the aggregated four-dose groups, the number of cases of severe Covid-19 per 100,000 person-days (unadjusted rate) was 1.5, compared to 3.9 in the three-dose group, and 4.2 in the internal control group. The adjusted rate of severe Covid-19 in the fourth week after receiving the fourth dosage was lowered by a factor of 3.5 (95 per cent confidence interval [CI], 2.7 to 4.6) than the three-dose group and a factor of 2.3 lower than the internal control group (95 per cent CI, 1.7 to 3.3).

During the six weeks following the fourth dose, protection against serious sickness did not fade. 

The study found that after the fourth dose of the BNT162b2 vaccine, the rates of confirmed SARS-CoV-2 infection and severe Covid-19 were much lower than after the third dose. During the trial period, protection against infection diminished, while protection against the disease severity was maintained. (MedPage Today April 5, 2022; N Engl J Med DOI: 10.1056/NEJMoa2201570.)