COVID-19 Scan for Apr 06, 2022

Fourth COVID vaccine dose boosts protection against infection, severityA study in Israel during the Omicron variant surge finds that rates of COVID-19 infection and severe illness were lower after a fourth dose of the Pfizer/BioNTech vaccine than after three doses, and while protection against infection waned quickly after 4 weeks, protection against severe disease was still strong at 6 weeks.The study, published yesterday in the New England Journal of Medicine (NEJM), involved data from 1,252,331 people aged 60 years and older, who became eligible for a fourth COVID-19 shot in Israel on Jan 2, 2022.

The study period ran from Jan 10 to Feb 18 for severe illness and to Mar 2 for infection.The unadjusted rate of COVID-19 infections per 100,000 person-days among people who had received a fourth vaccine dose 8 days before was 1.5, compared with 3.9 in those who had received three doses and 4.2 in controls who had received a fourth dose 3 to 7 days before.After adjustment, the rate of severe COVID-19 in the fourth week after receipt of the fourth vaccine dose was lower than that of the three-dose group by a factor of 3.5 (95% confidence interval [CI], 2.7 to 4.6) and lower than that in controls by a factor of 2.3 (95% CI, 1.7 to 3.3).Vaccine protection against severe infection was stable for 6 weeks after the fourth dose.

The unadjusted rate of severe COVID-19 infection per 100,000 person-days was 177 in fourth-dose recipients, 361 in the three-dose group, and 388 in controls.The adjusted rate of infection among those who had received a fourth dose 4 weeks earlier was lower than that in the three-dose group by a factor of 2.0 (95% CI, 1.9 to 2.1) and lower than that of controls by a factor of 1.8 (95% CI, 1.7 to 1.9)."These