Abstract
BACKGROUND: The Haemophilus influenzae type b (Hib) vaccination has well-established safety and efficacy in preventing Hib and reducing related morbidity and mortality worldwide. China has a high disease burden of Hib yet a low coverage rate of Hib vaccines and remains the only WHO member country not including the Hib vaccine in its National Immunization Program (NIP), partly due to insufficient surveillance data on its safety. This study analyzed all adverse events following immunization (AEFIs) after Hib monovalent vaccination in Zhejiang Province from 2017 to 2023 to provide evidence for formulating relevant immunization strategies. METHODS: Hib vaccine-related AEFIs in Zhejiang Province from 1 January 2017, to 31 December 2023, were collected through the Chinese National AEFI Information System (CNAEFIS) for a descriptive epidemiological analysis. RESULTS: From 2017 to 2023, a total of 1740 Hib vaccine-related AEFIs were reported (incidence rate: 63.01/100,000 doses) (95%CI: 60.12/100,000 doses-66.04/100,000 doses), including 1577 common adverse reactions (57.10/100,000 doses) (95%CI: 54.35/100,000 doses-59.99/100,000 doses), 139 rare adverse reactions (5.03/100,000 doses) (95%CI: 4.26/100,000 doses-5.94/100,000 doses), and 24 coincidental events (0.87/100,000 doses) (95%CI: 0.58/100,000 doses-1.29/100,000 doses). Most of the AEFIs were common adverse reactions that manifested mainly as fever, injection site redness and swelling, and crying. AEFIs were more likely to occur in male participants under the age of one, in summer and autumn, and during the booster immunity stage. The top three regions with the highest reported incidence rates of AEFIs were Jiaxing City (86.61/100,000 doses) (95%CI: 74.44/100,000 doses-100.77/100,000 doses), Hangzhou City (81.29/100,000 doses) (95%CI: 72.56/100,000 doses-91.07/100,000 doses), and Taizhou City (66.62/100,000 doses) (95%CI: 58.24/100,000 doses-76.21/100,000 doses). CONCLUSIONS: Our findings provide preliminary evidence of the safety profile of the Hib vaccine at a provincial level, which adds further support for its broader implementation in other provinces. Future multi-center studies are needed to construct a comprehensive vaccine evaluation framework and make multi-criteria decisions on the feasibility of incorporating the Hib vaccine into China's NIP.