Definite bacterial infection in recently vaccinated febrile infants

There is insufficient evidence regarding the best approach to evaluating recently vaccinated (RV) infants presenting to the paediatric emergency department with fever. The aim of the present study is to determine the prevalence of bacterial infections in infants presenting with fever within 72 h after vaccination.

We retrospectively reviewed the electronic medical record of infants aged between 6 and 12 weeks who presented with a fever ≥38°C to the emergency department from January 2016 to December 2018. Febrile infants who were vaccinated within 72 h prior to their emergency department presentation were matched to those who had not received their vaccines in the previous 72 h. Definite serious bacterial infection was diagnosed based on culture results.

A total of 198 infants (age: 9 ± 1.84 weeks, male: 119 (60.1%)) were enrolled in this study. Overall, 60 of 138 (30.3%) had received their vaccines within the previous 72 h. The prevalence of bacterial infection in RV infants was 5% compared to 15.2% in non-RV infants (P = 0.056). Interestingly, all vaccinated infants who had proven bacterial infection presented to the emergency department with fever within 24 h of vaccination, and all bacterial infections in that group were urinary tract infections.

The prevalence of bacterial infection among non-RV febrile infants is relatively higher than those RV. However, fever should not be attributed only to the vaccinations, and all febrile RV infants should be carefully evaluated, and at least urine testing should be performed regardless of the time of vaccination.