Adverse reactions to immunization with newer vaccines in the very preterm infant

Objective: To study the frequency and types of adverse reactions to currently available vaccines in very preterm infants. Methods: Case notes were obtained for very preterm infants <= 30 weeks' gestational age who received their first immunization at the Royal Women's Hospital, Melbourne, during 1999-2003. Data were extracted for the time periods 48 h before and 48 h after immunizations, with the data extraction blinded as to whether the period being evaluated was pre- or post-immunization. Data collected focused on the frequency and severity of apnoea, respiratory support, fever and clinical consequences of adverse reactions. Results: A total of 48 very preterm infants were immunized during the period; 37 infants had Comvax (Haemophilus influenzae type B and hepatitis B vaccine), Infanrix (diphtheria, tetanus and acellular pertussis vaccine) and inactivated poliomyelitis vaccine, and 11 infants had Comvax and Infanrix only. Their mean (SD) gestational age at birth was 26.4 (1.7) weeks with mean birthweight of 872 (235) g. The mean postnatal age at immunization was 76 (20) days. Low-grade fever (> 37.5 degrees C per axilla) occurred in 16 (33%) infants after immunization, but none before immunization (P < 0.001). There was no substantial change in recorded apnoea. No serious adverse events were noted. Four (8%) infants underwent a septic work up post-immunization. The C-reactive protein was increased in all four infants, but other tests for sepsis were negative. Conclusion: Fever remains a common adverse event following immunization of the preterm infant in spite of the development of a new generation of vaccines.