Subcutaneous versus intramuscular adult diphtheria-tetanus-acellular pertussis (TRIBIK®) vaccination in Japanese healthcare workers: A prospective observational safety study.

In Japan, the diphtheria-tetanus-acellular pertussis (DTaP) vaccine (TRIBIK®; BIKEN Co., Ltd., Japan) is the pertussis-containing vaccine used for adults, and the package insert specifies subcutaneous (SC) administration. Given the relatively high antigen content of TRIBIK®, local reactogenicity may be a concern. We evaluated whether intramuscular (IM) administration could reduce adverse reactions among healthcare workers. We conducted a prospective observational study among physicians and nurses at a tertiary children's hospital in Japan. Participants selected SC or IM administration and received 0.5 mL TRIBIK®. Local reactions (pain by numerical rating scale [NRS], erythema, induration) and systemic symptoms (fever, fatigue, headache, appetite loss) within 7 days were collected via online questionnaires. Forty-five healthcare workers were enrolled (SC, n = 18; IM, n = 27), with no significant differences in baseline characteristics. The IM group reported significantly lower injection-site pain than the SC group (median NRS 1.0 vs 3.0; p = 0.021). The incidence of erythema and induration was also significantly lower with IM administration (p = 0.016 and p < 0.01, respectively). Systemic adverse events did not differ significantly between the two groups, and no participant required medical consultation. IM administration was associated with reduced local reactogenicity without increased systemic events in Japanese healthcare workers. Allowing IM administration could improve tolerability and support occupational pertussis booster programs in Japan; larger studies including immunogenicity are warranted.