BACKGROUND: The introduction of Haemophilus influenzae type b (Hib) conjugate vaccines in France led to low invasive Hib disease incidence for two decades. In 2013, the vaccination schedule changed from 3+1 to 2+1 ((2, 4, and 11 months). Hib vaccination has been mandatory for children born since 2018. Despite vaccination coverage exceeding 95%, invasive Hib disease has increased since 2018. This study reports trends and characteristics of cases in mainland France from 2018 to 2024. METHODS: Cases were children under five years old with invasive Hib disease confirmed by culture or PCR by the National Reference Center for Haemophilus influenzae. Vaccination status was reported by biologists/clinicians or by regional investigation teams. Cases were described by age and vaccination status (unvaccinated, partially vaccinated, correctly vaccinated). Vaccine failure was defined as invasive Hib disease despite completion of the three-dose series. Vaccine effectiveness (VE) for three doses was estimated using the screening method in children aged 2-4 years. RESULTS: The incidence of invasive Hib disease among children under 5 years old increased during the 2018-2024 period, peaking in 2021 with 46 cases (1.4/100,000 children). From 2018 to 2024, 181 cases of invasive Hib disease were reported. Among those aged 6-11 months (n=60), 76.7% were correctly vaccinated with two doses. In children ≥12 months (n=65), 67.7% were correctly vaccinated with three doses and there were 44 vaccine failures. The estimated VE for three doses was 91.2% [95% confidence interval: 76.3-96.8%]. DISCUSSION - CONCLUSION: Invasive Hib disease increased among children under 5 years old in France during 2018-2024, and most cases were correctly vaccinated. VE estimate do not suggest waning immunity. The reasons that may explain the increase in invasive Hib cases remain uncertain. Our results call for further studies on the VE following the two primary doses and the impact of vaccination on carriage.
Auteur : Barret Anne-Sophie, François Céline, Deghmane Ala-Eddine, Lefrançois Rémi, Mercuriali Lilas, Thabuis Alexandra, Marie Cécile, Carraz-Billat Elise, Zanetti Laura, Parent du Châtelet Isabelle, Taha Muhamed-Kheir
Vaccine, 2025, vol. 62, p. 127499
