Does the 2+1 vaccination schedule for Haemophilus influenzae type b increase case numbers?

Presented by

Dr Stéphanie Jacquinet , Sciensano, Belgium

Conference

ESCMID Vaccines 2025

The introduction of a 2-dose primary series followed by one booster vaccination for Haemophilus influenzae type b (Hib) has been linked to rising case numbers in certain, but not all, European countries.

The number of yearly Hib cases reported to the European Centre for Disease Control (ECDC) between 2000 and 2023 was analysed by country, vaccination schedule, and annual vaccination coverage. Countries included were members of the European Union or the European Economic Area, but Bulgaria and Croatia were excluded due to a lack of serogroup B-specific data.

Dr Stéphanie Jacquinet (Sciensano, Belgium) presented the results. In total, 16 of the 28 countries analysed used a 2+1 vaccination schedule, while the remainder followed a 3+1 schedule [1]. An increase in Hib cases was observed in Germany even before the introduction of the 2+1 schedule, while the Netherlands experienced a rise immediately after adoption. In contrast, Slovakia, Austria, and the Nordic countries did not report any increase in cases. The vaccination coverage was below 90% in Germany and the Netherlands; however, an increase in cases was also observed in France several years after the switch to 2+1, despite coverage remaining consistently near 100%. None of the analysed countries reverted to a 3+1 schedule after moving to a 2+1 schedule.

The authors concluded that the observed increases are most likely multifactorial. “In addition to the vaccination schedule, coverage, type of vaccine, and age for booster, further elements should be explored, such as surveillance quality and early childcare attendance.”

Jacquinet S, et al. Hib trends and vaccine schedule: a comparison between European countries. 6th ESCMID Vaccines, 10–13 September 2025, Lisbon, Portugal.

Medical Conferences

Does the 2+1 vaccination schedule for Haemophilus influenzae type b increase case numbers?

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