The risk of death from COVID-19 decreases significantly after vaccination but this protection diminishes after six months, providing evidence for continued booster doses, a new study has found.

Researchers from the UK Health Security Agency (UKHSA) analyzed more than 10 million cases of COVID-19 in adults between May 2020 and February 2022. Their findings are published in the Journal of the Royal Society of Medicine (JRSM).

The Case Fatality Risk (CFR)—the proportion of cases that resulted in death—was cross-referenced with vaccination status, revealing a clear association between vaccination and reduced mortality. Notably, the study highlights a crucial timeframe—within six months of the last vaccine dose—when CFR was consistently at its lowest across all age groups. After this, the protective benefit began to wane and CFR increased.

The research underscores the success of the COVID-19 vaccination program in reducing mortality rates.

Among adults over 50, CFR was 10 times higher in the unvaccinated (6.3%) compared to those who had been vaccinated within six months prior to testing positive (0.6%). The study also reveals a steep decline in CFR in early 2021, aligning with the initial vaccine rollout.

Florence Halford from the UKHSA's COVID-19 Vaccines and Epidemiology Division said, "COVID-19 case fatality risk reduced after vaccination, with the lowest seen across all age bands when vaccinated up to six months prior to the specimen date. This provides some evidence for continued booster doses in older age groups."