Effectiveness of first and second boost COVID-19 vaccination in healthy adults during BA.5.2/BF.7 surge in China.

With the development of the SARS-CoV-2 pandemic, there have been doubts about the necessity of vaccine boosters for healthy adults. However, due to the lack of relevant evidence, current research is unable to provide reliable medical advice for COVID-19 boost in healthy adults. We conducted a retrospective observational study to evaluate the effectiveness of different COVID-19 vaccination regimens by investigating the SARS-CoV-2 infection status of healthy donors in Southeast China. From December 2022 to February 2023, 737 healthy adult blood donors were analyzed. Results showed that any COVID-19 vaccine boosts reduced the risk of Omicron BA.5.2/BF.7 infection compared to only receiving prime vaccination (rVE = 16%, 95%CI = 4, 27%). The second boost further enhanced vaccine effectiveness compared to the received first booster (rVE = 39%, 95%CI = 16, 55%). Through retrospective observation of healthy adults during the BA.5.2/BF.7 surge in China, we found that boost vaccinations significantly reduce the risk of SARS-CoV-2 infection and disease. Findings show healthy adults benefit from boost vaccinations, even if not at high-risk for severe COVID-19.