Post-marketing surveillance study of the DTaP2-IPV-HB-Hib (Hexyon) vaccine administered in preterm infants in the Apulia region, Italy, in 2017.

Recommendations in many countries state that preterm infants (PTIs) should receive the same routine immunization schedule and timing as for full-term births, according to their chronological age. Data regarding hexavalent vaccine safety in PTIs are still limited. We conducted a post-marketing surveillance study of the DTaP2-IPV-HB-Hib vaccine administered to PTIs in Apulia region, Italy. We identified PTIs by selecting the hospital discharge records of infants born between January and June 2017 using the DRG and ICD-9-CM codes for preterm birth, and we matched these data with records included in the regional immunization registry. We analyzed coverage and timeliness of vaccination. To investigate adverse events (AEs) after the first dose, we interviewed via phone the parents of PTIs vaccinated with at least one dose of the DTaP2-IPV-HB-Hib vaccine. At the time of our analysis (31.12.2017), 866/936 (92.5%) PTIs received the first dose of hexavalent vaccine and 539/936 (57.6%) were vaccinated by the third month of age, as recommended; 700/866 (80.8%) received the DTaP2-IPV-HB-Hib vaccine. The parents of 339 PTIs vaccinated with the DTaP2-IPV-HB-Hib vaccine reported local pain as the most common reaction (35.7% of the children). Erythema, swelling, induration and nodule were also reported in about 25% of the children. Systemic adverse events were generally rarer than local reactions. No serious AEs were reported. Our findings showed that more than 40% of PTIs received delayed hexavalent vaccination. This study showed a reassuring safety profile of the vaccine in the preterm population and may be considered as a pilot for further real-world studies.