The following is a summary of “Effectiveness of mRNA COVID-19 vaccines and hybrid immunity in preventing SARS-CoV-2 infection and symptomatic COVID-19 among adults in the United States,” published in the January 2025 issue of Infectious Disease by Feldstein et al. 

Researchers conducted a retrospective study to examine the protection against SARS-CoV-2 infection provided by vaccination and hybrid immunity considering emerging variants.  

They analyzed data from 3 cohort studies conducted between September 1, 2022, and July 31, 2023, to estimate COVID-19 vaccine effectiveness (VE) against SARS-CoV-2 infection and symptomatic COVID-19 in adults with and without prior infection in the United States. Participants provided weekly nasal swabs and annual blood samples and completed surveys on vaccination status and prior infection history. The SARS-CoV-2 testing was performed on the swabs using molecular methods and VE was estimated using Cox proportional hazards models, adjusting for covariates, and calculated based on prior infection and vaccination recency.  

The results showed that among 3,344 adults, the adjusted COVID-19 VE of the bivalent vaccine against infection was 37.2% (95% CI: 12.3-55.7%) within 7-59 days and 21.1% (95% CI: -0.5-37.1%) within 60-179 days after vaccination, compared to unvaccinated individuals or those who received a monovalent vaccine ≥180 days prior. The adjusted VE of the bivalent vaccine, combined with prior infection, was 62.2% (95% CI: 46.0-74.5%) within 7-179 days and 39.4% (95% CI: 12.5-61.6%) ≥180 days, compared to naive individuals who were unvaccinated or received a monovalent vaccine ≥180 days prior.  

Investigators concluded the adults with a history of prior infection exhibited high protection against infection and symptomatic illness, while recent vaccination alone provided moderate protection against these outcomes. 

Source: academic.oup.com/jid/advance-article/doi/10.1093/infdis/jiaf007/7945315