A large observational study has found that booster vaccination against COVID-19 was associated with a substantially lower risk of hospitalisation and death among adults aged 50 and over in England, though protection declined over time.
Published in Vaccine, the research was led by the universities of Bristol and Oxford and analysed linked GP and hospital records from over 3 million adults who received an autumn 2022 booster, matched with an equal number of unboosted individuals with similar characteristics, including age, prior vaccination history, clinical vulnerability, and geographical region. Participants were followed for approximately one year.
Among those followed up, boosted individuals showed notably lower rates of COVID-19 hospitalisation and death over 350 days compared to unboosted counterparts. The risk reduction was roughly halved for both outcomes. Protection was strongest in the first 70 days following the booster and waned progressively thereafter.
Both the Moderna and Pfizer-BioNTech bivalent BA.1 booster vaccines performed similarly for COVID-19-related outcomes. A slightly higher rate of non-COVID-19 mortality was observed in the Moderna group, though the clinical significance of this difference is unclear.
As a methodological check, the study examined fracture risk, an outcome not expected to be causally linked to vaccination. A small apparent reduction was found in boosted individuals, suggesting some residual confounding may be present, though researchers noted the much smaller effect size for fractures supports the overall validity of the findings.
The authors conclude that the results reinforce the value of booster vaccination for reducing severe COVID-19 outcomes in older adults, consistent with evidence from the initial vaccination programme.
