Seroprevalence of diphtheria, tetanus, pertussis among healthcare workers (HCWs) – A cross-sectional study at the National Centre for Infectious Diseases and Tan Tock Seng Hospital, Singapore

Immunization in healthcare workers (HCWs) is important to minimize VPD (vaccine-preventable diseases) outbreaks in the healthcare setting, including diphtheria and pertussis, in the context of the global resurgence of VPD. This study aimed to assess tetanus toxoid, reduced diphtheria, acellular pertussis (Tdap) vaccination coverage, seroprevalence, and factors associated with seropositivity among HCWs in Singapore. We conducted a cross-sectional study utilizing residual sera and occupational health vaccination records from HCWs enrolled in a COVID-19 seroepidemiology study in 2020 at our institutions. Serological ELISAs (Euroimmun) for diphtheria, tetanus, and pertussis were performed. Factors associated with seropositivity were analyzed using logistic regression. Time since vaccination and seropositivity were compared using non-parametric statistical tests. The Tdap vaccine coverage was 74.6% amongst the 284 included HCWs. Seropositivity for diphtheria, tetanus, and pertussis were 95.1%, 96.1% and 13.7% respectively. Tdap vaccination within 10 y was associated with diphtheria and tetanus seropositivity [adjusted odds ratios (aORs) 7.58 (95% CI 1.99-33.93), 8.57 (95% CI 2.19-42.78) respectively], adjusted for other variables. Increasing age was negatively associated with diphtheria and tetanus seropositivity; aOR 0.06 (95% CI 0.01-0.36) for diphtheria and 0.17 (95% CI 0.03-0.94) for tetanus in HCWs aged ≥ 45 (reference 21-30 y). Pertussis seropositive HCWs were vaccinated more recently from serum collection compared to seronegative HCWs (Median 198.5 d vs 449 d, <i>p</i> < .05). High Tdap vaccination coverage among HCWs has resulted in strong immunity against diphtheria and tetanus but seems to wane with age. High immunization coverage along with infection prevention measures is essential to prevent VPD outbreaks.