Post-marketing safety surveillance of Haemophilus influenzae Type b conjugate vaccine in children aged 3 months to 5 years in Jiangsu, China.

This study evaluates the post-marketing safety profile of a Haemophilus influenzae Type b (Hib) conjugate vaccine in children aged 3 months to 5 y in China. A prospective, observational, multi-center, post-marketing safety surveillance study of a monovalent Hib conjugate vaccine manufactured by Chengdu Olymvax Biotechnology Inc. was conducted across 20 districts in Jiangsu Province, China, from June 2020 to December 2021. The study enrolled 2,714 children in the active surveillance group and 6,347 children in the passive surveillance group. For active surveillance, guardians recorded all adverse events occurring within 30 d after each vaccine dose in diary cards, regardless of suspected causality. Serious adverse events were captured through spontaneous guardian reports or through regular investigator follow-up from the first dose through 6 months after completion of the primary Hib conjugate vaccine series. During passive surveillance, suspected adverse events following immunization (AEFI) of the Olymvax Hib vaccine were registered and reported through China National Adverse Event Following Immunization (AEFI) Surveillance System. Active surveillance revealed an overall adverse event incidence of 6.7% (181/2,714), with 6.3% (170/2,714) classified as adverse reactions, predominantly mild to moderate in severity (Grade 1-2: 6.0%; Grade 3: 0.3%). Passive surveillance identified a substantially lower adverse reaction incidence of 0.33% (21/6,347), with pyrexia (0.25%) being the most frequent. The AEFI incidence rate in passive surveillance was significantly lower than in active surveillance (