Study: Booster vaccines reduced severe COVID outcomes

Booster vaccines reduced the risk of COVID‑19–related hospitalization and death, according to a new study of over 3 million adults who had the autumn 2022 vaccine in England. The research led by the universities of Bristol and Oxford, provides further evidence of the effectiveness of booster vaccination against COVID-19.

The study, published in Vaccine today [18 February], also found that this effectiveness was similar for Moderna (BA.1 mRNA-1273) and Pfizer-BioNTech (BA.1 BNT162b2) booster vaccines, but protection declined over time.

Previous work has shown the initial COVID-19 vaccination was effective in reducing the risk of hospitalization and death due to COVID-19. This latest research, carried out at the National Institute for Health and Care Research (NIHR) Bristol Biomedical Research Centre (BRC), looked at the impact of giving people a booster vaccine.

The team investigated the effectiveness of Moderna and Pfizer-BioNTech booster vaccines administered during the autumn 2022 booster campaign in England for previously vaccinated people age 50 or over. 

The NHS England approved study analysed linked GP and hospital records available within the OpenSAFELY research platform. The team compared 3,464,877 adults eligible for booster vaccination during the autumn 2022 COVID-19 vaccine rollout with the same number of unboosted people.

They matched them with people who were similar in terms of age, date of last COVID-19 vaccine dose, brand of prior vaccination, clinical vulnerability and geographical region. The researchers then followed these people up for nearly a year and tracked hospitalization and death due to COVID-19.

Across 2.5 million people followed up over a year, the study recorded 14,436 COVID‑19 hospitalizations, 1,152 COVID‑19 deaths, 32,184 non‑COVID‑19 deaths and 52,758 fractures.

The study found boosted individuals had much lower 350‑day risks of COVID‑19 hospitalisation (3.78 vs 6.81 per 1,000) and death (0.29 vs 0.61 per 1,000). Boosters halved the risks of COVID‑19 hospitalisation and death. Protection waned over time, strongest in the first 70 days. Moderna and Pfizer‑BioNTech boosters performed similarly for COVID‑19 outcomes, though non‑COVID‑19 mortality was slightly higher in the mRNA‑1273 group.

The study also assessed the relationship between booster vaccination and fracture, an outcome not considered likely to be causally related. A small reduction in fracture risk was found for boosted individuals. This suggests that not all confounders (common causes of booster vaccinations and outcomes) were accounted for, but the much smaller effect for fracture is reassuring for the validity of the study's conclusions.

Dr Paul Madley-Dowd, Research Fellow in Medical Statistics and Health Data Science, and corresponding author at University of Bristol, said: "Our findings reinforce the importance of booster vaccination against COVID-19 among people over 50 years old.

"The study also provides further evidence that COVID-19 booster vaccinations reduced the risk of hospitalization and death."

This work was funded by NHS England; Wellcome Trust; MRC; NIHR; NIHR Bristol BRC; OpenSAFELY; and the Bennett Institute for Applied Data Science.