mRNA Vaccine Booster Highly Effective Among US Veterans With Comorbidities

A messenger RNA (mRNA) vaccine booster was highly effective against infection, hospitalizations, and death among an older population of US veterans, according to findings recently published in BMJ Open.

“Although the effectiveness of booster vaccination against infection was moderately higher against Delta than against the Omicron SARS-CoV-2 variant, effectiveness against severe disease and death was similarly high against both variants,” wrote study authors.

To estimate the vaccine effectiveness of second and third doses of mRNA vaccines against infection and COVID-19 related hospitalization and death, researchers conducted a matched test negative case control study.

Electronic health record data was extracted from the Veterans Health Administration and included 114,640 veterans who had a SARS-CoV-2 test between November 2021 and January 2022.

Of the patients included in the study, 88% were male, 59% were non-Hispanic white, and the majority were aged 65 years or older (52%).

During the Omicron period, booster doses had higher estimated vaccine effectiveness (64%; 95% CI, 63 to 65) when compared to two-dose vaccination (12%; 95% CI, 10 to 15). The vaccine-effectiveness against infection for the Delta period was 90% (95% CI, 88 to 92) among boosted vaccinees, higher than the VE among two-dose vaccinees (54%; 95% CI, 50 to 57). 

Booster dose vaccine effectiveness against hospitalization was 89% (95% CI, 88 to 91) during Omicron and 94% (95% CI, 90 to 96) during Delta; two-dose vaccine effectiveness was 63% (95% CI, 58 to 67) during Omicron and 75% (95% CI, 69 to 80) during Delta. 

Booster dose vaccine effectiveness against death was 94% (95% CI, 90 to 96) during Omicron and 96% (95% CI, 87 to 99) during Delta.

Reference:
Young-Xu Y, Zwain GM, Izurieta HS, et al. Effectiveness of mRNA COVID-19 vaccines against Omicron and Delta variants in a matched test-negative case-control study among US veterans. BMJ Open. 2022; 12(8):e063935. doi:10.1136/bmjopen-2022-063935