BMC Infectious Diseases | 2021
Haemophilus influenzae type b (Hib) seroprevalence in France: impact of vaccination schedules
Abstract
Background Haemophilus influenzae serotype b (Hib) conjugate vaccine was introduced in France in 1992 as a 3\u2009+\u20091 scheme at 2, 3, and 4\u2009months (primary vaccination) with a booster at the age of 16–18\u2009months. The vaccination was simplified in 2013 to a 2\u2009+\u20091 scheme at 2 and 4\u2009months (primary immunization) and a booster at the age of 11\u2009months. The coverage was 95.4% in France at 24\u2009months in 2017. During the period 2017–2019 the number of Hib invasive infections increased with several cases of vaccine failure. Methods The numbers and proportions of Hib invasive isolates during the period 2017–2019 were compared and vaccine failure cases were explored. A seroprevalence study was performed by measuring anti-polyribosyl-ribitol phosphate (PRP) IgG concentrations by ELISA among children <\u20095\u2009years of age at the time of sampling covering the periods of the 3\u2009+\u20091 or 2\u2009+\u20091 schemes of Hib vaccination. A collection of residual 232 sera was tested (group 3\u2009+\u20091 n \u2009=\u2009130) and (group 2\u2009+\u20091, n \u2009=\u2009102) was used. Results Anti-PRP IgG concentrations were significantly higher in toddlers of 2\u2009years (median 2.9\u2009μg/ml) in the 3\u2009+\u20091 group while these concentrations showed a median of 0.58\u2009μg/ml among children in 2\u2009+\u20091 group. The proportion of children of 2\u2009years of age who achieved 1\u2009μg/ml threshold (56%) was higher in the 3\u2009+\u20091 group than that observed in the 2\u2009+\u20091 group (25%). All the detected cases of vaccine failure received the 2\u2009+\u20091 scheme and anti-PRP IgG levels were less than 1\u2009μg/ml at the admission. However, these levels increased significantly 1 month after the admission suggesting a secondary immune response to the Hib infection. Conclusions The simplification of the vaccination to a 2\u2009+\u20091 scheme seems to reduce the level of anti PRP IgG. Hib antibodies wane rapidly after the 11\u2009months booster and may not be enough to ensure long term protection. Surveillance of cases and monitoring of titres need to be continued to inform future vaccination policy.