Vaccine effectiveness against infection with delta variant declines with increasing time since vaccination
WEDNESDAY, Dec. 15, 2021 (HealthDay News) — Two doses of mRNA-1273 vaccine are highly effective against multiple severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants, according to a study published online Dec. 15 in The BMJ.
Katia J. Bruxvoort, Ph.D., M.P.H., from Kaiser Permanente Southern California in Pasadena, and colleagues examined the effectiveness of the mRNA-1273 vaccine against SARS-CoV-2 variants and against the delta variant in a test negative case-control study. A total of 8,153 cases with SARS-CoV-2 infection were matched in a 1:5 ratio to test negative controls. The odds of vaccination among cases versus controls were compared. At the time of the study, the omicron variant had not yet been detected in the Southern California region.
The researchers found that the two-dose vaccine effectiveness was 86.7, 98.4, 90.4, 96 to 98, and 79.9 percent against infection with the delta variant, alpha variant, mu variant, other identified variants, and unidentified variants (specimens that failed sequencing), respectively. Vaccine effectiveness was 97.5 percent against hospital admission with the delta variant. There was a decrease observed in vaccine effectiveness against infection with the delta variant from 94.1 to 80.0 percent at 14 to 60 days after vaccination and 151 to 180 days after vaccination, respectively. For non-delta variants, waning was less pronounced. People aged 65 years and older had lower vaccine effectiveness than those aged 18 to 64 years (75.2 versus 87.9 percent). The vaccine effectiveness of one dose was 77.0 percent against delta infection.
“This study provides reassuring evidence of the effectiveness of two doses of mRNA-1273 in preventing infection with SARS-CoV-2 and hospital admission with COVID-19 due to variants including delta,” the authors write.
Several authors disclosed financial ties to pharmaceutical companies, including Moderna, which manufactures the mRNA-1273 vaccine and funded the study.
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