Antibody Responses Elicited by mRNA Vaccination in Firefighters Persist Six Months and Correlate Inversely with Age and Directly with BMI

Knowledge regarding the sustainability of immune responses after COVID-19 vaccination are important, e.g., to decide whom and when to booster. Thus, we analyzed antibody titers in firefighters six months after vaccination with the mRNA-based vaccine Comirnaty. SARS-CoV-2 spike-binding antibodies (bAb) were quantified and compared to peak responses determined in healthcare workers (HCW). For the firefighters, neutralizing antibodies (nAb) were also analyzed. Six months after the second vaccine dose, all analyzed firefighters had detectable bAb, and 91% exhibited nAb titers above 1:16. However, actual titers six months after vaccination were over 12-fold lower than in the HCW control group four weeks after vaccination. bAb and nAb responses showed a significant correlation, and age correlated inversely with antibody responses. Unexpectedly, participants with a body mass index over 25 had higher neutralization titers after six months. All participants with very low neutralization titers were offered booster vaccination. The booster vaccination improved the extent and sustainability of antibody responses.Funding Information: The study was board funded.Conflict of Interests: The authors declare no competing interests.Ethical Approval: The virus isolation and the collection of serum samples have been approved by the ethics committee of the Medical Faculty of the University of Duisburg-Essen (20-9511-BO, 20-9512-BO, 21-10176-BO, 21-10005-BO). Informed consent was obtained from all study participants. All work with infectious SARS-CoV-2 was conducted in a biosafety level 3 laboratory according to the regulations of the local authorities.