Haemophilus influenzae type b (Hib) seroprevalence and current epidemiology in England and Wales.

INTRODUCTION: The introduction of the Hib conjugate vaccine in the United Kingdom resulted in a rapid decline in invasive Hib disease across all age groups. However, a resurgence in 2000-2002 prompted the introduction of additional control measures, including a routine 12-month booster in 2006. Here we describe results from a national serosurvey in children eligible for the 12-month booster and recent Haemophilus influenzae epidemiology in England and Wales. METHODS: A national serosurvey was performed to determine the prevalence of anti-polyribosyl-phosphate (anti-PRP) IgG antibodies in 1000 residual samples from children up to 8 years of age in 2013-2014. Data were compared to previous national serosurveys performed by the same laboratory. Current epidemiology of invasive H. influenzae disease in England and Wales is also reported. RESULTS: Median anti-PRP IgG concentrations were highest among 1 year olds at 4.5 µg/mL (95%CI, 0.93-33.6; n = 55) and then declined rapidly but remained ≥1.0 µg/mL across the age-groups in the cohort eligible for the 12-month booster. Overall, 89% of children (719/817) had anti-PRP concentrations ≥0.15 µg/mL, the putative threshold for short-term protectionagainst invasive Hib disease. During 2012-2016, annual Hib disease incidence remained below one case per million population, with only 67 of 3523 (2.5%) laboratory-confirmed H. influenzae cases and one case of Hib meningitis during the 5-year period. There were only two deaths within 30 days over the five-year period (case fatality rate, 3.0%). CONCLUSIONS: Hib control in England and Wales is currently the best achieved since the vaccine was introduced more than two decades ago. However, Hib antibodies wane rapidly after the 12 months booster. Although most children remain protected against disease, antibody levels may not be high enough to prevent carriage among toddlers. Ongoing monitoring is essential to inform future vaccination policy