The safety of immunizing with tetanus-diphtheria-acellular pertussis vaccine (Tdap) less than 2 years following previous tetanus vaccination: Experience during a mass vaccination campaign of healthcare personnel during a respiratory illness outbreak.

BACKGROUND: Tdap is recommended for health care personnel (HCP) aged <65 years who received tetanus diphtheria or tetanus toxoid immunization (Td/TT) ≥2 years earlier. During a medical center Tdap vaccination campaign, we assessed the safety of use of a Td/TT to Tdap interval <2 years in HCP. We also describe reactogenicity in HCP who were aged ≥65 years or pregnant.
METHODS: HCP vaccinated with Tdap were surveyed to assess time since last Td/TT (≥2 years vs. <2 years), age, pregnancy status, and injection site adverse events (AEs) during the 2 weeks after Tdap. AE rates were calculated and compared by non-inferiority analysis using a predetermined margin of 10%. We searched clinic logbooks to assess for clinically important adverse events during the 2 months after Tdap.
RESULTS: Of the 4524 vaccinated HCP, 2221 (49.1%) completed a safety survey which met criteria for analysis. Non-inferiority analysis found that rates of moderate and/or severe injection site AEs were not significantly greater in those vaccinated <2 years than in those vaccinated ≥2 years after previous Td/TT. Three serious adverse events were reported during the 2 months after vaccination, none in persons who were ≥65 years, pregnant or received Td/TT <2 years before.
CONCLUSIONS: Our findings add to the body of evidence that a short interval between Td/TT and a single dose of Tdap is safe.