Denmark’s National Research Institute Conducts 1 Million Participant Cohort Study of XBB.1.5 Booster—No Safety Signals

Wha is the association between the XBB.1.5-containing vaccine administered as a fifth COVID-19 vaccine dose and the risk of 28 identified adverse events in Denmark among persons aged 65-years and up? An important new study led by Statens Serum Institut (SSI), Epidemiology Research group investigated by reporting on the safety of the COVID-19 mRNA XBB.1.5 booster vaccine. Niklas Worm Andersson, M.D.  and colleagues By cross-linking nationwide healthcare and demography registers on an individual level, the study team was able to design and conduct the study cohort covering all individuals in Denmark aged 65 and older who had received four (4) COVID-19 vaccine doses. Classifying vaccination status in a time, varying manner, the study covered the period September 15, 2022, which represents the national rollout date of the fourth booster jab until January 8, 2024. The study protocol called for the adaption of 28 adverse events based on prioritized lists of adverse events of special interest to COVID-19 vaccines. Each outcome was studied separately and identified as any first hospital contact where an outcome diagnosis was recorded. The diagnosis date served as the event date. The nationwide cohort of over 1 million adults aged 65 years and older observed within 28 days after receiving the jab no increased risk of 28 adverse events ensuing vaccination with a monovalent XBB.1.5-containing vaccine.

The output was published in JAMA Monday February 26, 2024.