What is the incidence of Haemophilus influenzae type b (Hib) infections and disease after implementation of a universal 4-dose vaccination policy?

From the Guidelines

The incidence of Haemophilus influenzae type b (Hib) infections and disease has dramatically decreased to less than 1 case per 100,000 children under 5 years of age since the implementation of universal 4-dose vaccination policies.

Key Points

• In countries with high vaccination coverage, invasive Hib disease has declined by more than 95% compared to pre-vaccine era rates 1.
• The most significant reductions have been observed in meningitis, epiglottitis, and bacteremia caused by Hib.
• The 4-dose schedule (typically given at 2,4,6, and 12-15 months) has been particularly effective because it provides both primary immunity and a booster dose to ensure long-lasting protection.
• This dramatic reduction demonstrates the concept of herd immunity, where high vaccination rates protect even unvaccinated individuals by reducing overall pathogen circulation in the community 1.

Epidemiology and Vaccination

The success of Hib vaccination represents one of the most remarkable achievements in modern preventive medicine, effectively controlling what was once a leading cause of bacterial meningitis and other serious infections in young children.

• Studies have demonstrated that vaccination with Hib conjugate vaccine leads to decreases in oropharyngeal colonization among both vaccinated and unvaccinated children 1.
• The prevalence of Hib carriage has decreased among preschool-aged children from 2%–7% in the prevaccine era to <1% in the vaccine era 1.

Recommendations

The current recommendation is to routine vaccination with a licensed conjugate Hib vaccine for infants aged 2 through 6 months (2 or 3 doses, depending on vaccine product) with a booster dose at age 12 through 15 months 1.

• ACIP also recommends vaccination for certain persons at increased risk for Hib disease, such as those with early component complement deficiencies, immunoglobulin deficiency, anatomic or functional asplenia, or HIV infection 1.

From the Research

Incidence of Haemophilus influenzae type b (Hib) Infections

• The incidence of Hib disease in children less than 5 years old has declined by 95% from 41 cases per 100,000 in 1987 to 2 cases per 100,000 in 1993, following the introduction of Hib conjugate vaccines 2.
• A study found that the incidence of invasive Hib disease among children <5 years of age decreased by 99% in the United States since the introduction of effective vaccines 3.
• The age-specific incidence of Hib disease among children less than 5 years old decreased by 71% from 37 per 100,000 persons in 1989 to 11 per 100,000 persons in 1991 4.
• By 1996, the incidence of Hib invasive disease among children aged <5 years had declined by >99% 5.
• The estimated mean annual incidence of H. influenzae infection was 1.62 cases per 100 000 population during 1999-2008, with 15.3% of cases being fatal 6.

Disease Trends After Vaccination Policy Implementation

• The introduction of Hib conjugate vaccines has led to a dramatic reduction of Hib disease in young children, shifting the epidemiological trends of invasive H. influenzae 6.
• Despite the decline in Hib disease, a considerable burden of non-Hib disease is still present in the oldest and youngest age groups 6.
• There is no evidence of substantial replacement disease with non-b serotypes in young children in the United States 6.
• The incidence of reported Hib invasive disease remains low, with an annual average incidence of 0.2 and 0.18 per 100,000 population from 1998 to 2007 and 2008 to 2009, respectively 3.