Seniors who receive fourth shots of mRNA vaccines benefit from boosts in short-term protection against SARS-CoV-2 infection and longer-term protection against hospitalization and death, a large new study from Israel has found.
In January, the country’s authorities approved fourth doses, or second boosters, of the Pfizer-BioNTech vaccine for people aged 60 years and older, as well as to the medically vulnerable and to healthcare workers. Qualified patients had received their third dose at least four months earlier. Omicron was the dominant virus variant during the study period.
The fourth shot delivered moderate additional protection against omicron infection when compared to a third dose, investigators found.
Maximum protection occurred at four weeks after vaccination and then began to wane. But increased protection against severe illness held strong at six weeks — the end of the study period. At that point, patients showed no signs of decreasing immunity, the authors reported.
“Overall, these analyses provided evidence for the effectiveness of a fourth vaccine dose against severe illness caused by the omicron variant,” they concluded.
The study was published in the New England Journal of Medicine.