Fourth COVID vaccine dose gives 76% added protection against death

Compared with a third vaccine dose, a fourth dose of the Pfizer/BioNTech COVID-19 vaccine lowered the risk of infection, symptomatic infection, hospitalization, severe illness, and death 52% to 76%—depending on the measure—amid the Omicron surge among older adults, finds a new Israeli study.Protection against infection waned, however, after 5 weeks, but not protection against severe COVID-19.

The findings were published yesterday in the New England Journal of Medicine.Clalit Research Institute investigators in Tel Aviv led the study, which compared the effectiveness of a fourth vaccine dose 8 days earlier—after a third dose at least 4 months before—relative to a third dose only (control group) and a fourth dose 3 to 7 days earlier (internal control group), among 1,252,331 participants 60 and older from Jan 3 to Feb 18, 2022.Greater, more durable protection against severe outcomesSeven to 30 days after the fourth COVID-19 dose, vaccine effectiveness (VE) relative to the third dose was estimated at 45% against infection (95% confidence interval [CI], 44% to 47%), 55% against symptomatic illness (95% CI, 53% to 58%), 68% against COVID-19 hospitalization (95% CI, 59% to 74%), 62% against severe disease (95% CI, 50% to 74%), and 74% against death (95% CI, 50% to 90%).Fourteen to 30 days after the fourth dose, VE was 52% (95% CI, 49% to 54%) against infection, 61% (95% CI, 58% to 64%) against symptomatic illness, 72% (95% CI, 63% to 79%) against hospitalization, 64% (95% CI, 48% to 77%) against severe disease, and 76% (95% CI, 48% to 91%) against death.In the fourth week after the fourth dose, the adjusted infection rate was lower by a factor of 2.0 (95% CI, 1.9 to 2.1) than that in the three-dose group and lower by a factor