Progress towards meningitis prevention in the conjugate vaccines era

Efficacy and Prolonged Safety of Haemophilus influenzae Type b Conjugate Vaccines

OBJECTIVE

The purpose of this study was to find data proving the influence of the Haemophilus influenzae type b (Hib) conjugate vaccination on the frequency of invasive Hib illness.

METHODOLOGY

A systematic literature search was conducted on the PubMed database to identify peerreviewed publications pertaining to the epidemiology of Haemophilus influenzae meningitis, both before and after the introduction of Haemophilus influenzae type b (Hib) conjugate vaccines. The search query employed a combination of relevant keywords, including "invasive," "Haemophilus," "influenzae," "meningitis," and specific serotype b (Hib). Additionally, terms related to epidemiology, burden, risk factors, impact, Hib vaccine, Hib conjugate vaccine, combination vaccine, vaccine production, efficacy, immunisation coverage, surveillance, review, clinical aspects, outcomes, and various age groups (adults and children) were incorporated.

RESULT

The search encompassed articles published till now. Subsequently, relevant research papers concerning Haemophilus influenzae meningitis were subjected to a comprehensive review and analysis.

CONCLUSION

The Hib conjugate vaccination has shown to be extremely effective when administered to the entire population. However, changes to the immunisation protocol appear to be required in order to effectively manage invasive Hib illness.

Bacterial meningitis: the impact of vaccination

Acute bacterial meningitis remains an important cause of morbidity and mortality in children. Children <2 years of age are particularly susceptible to infection with encapsulated bacteria due to their immature response to polysaccharide antigens. Conjugate vaccines, which induce T cell memory, can provide immunological protection for these children. The Haemophilus influenzae type b (Hib) conjugate vaccine was the first such vaccine to become available. The efficacy of the vaccine has been quoted as being 98%. Its introduction was followed by a dramatic decrease in the incidence of all invasive Hib disease, including meningitis. This reduction was in part due to the ability of these vaccines to reduce nasopharyngeal carriage of the organism and thereby induce herd immunity. Different Hib vaccines use a variety of protein carriers and differ in their immunogenicity and efficacy. The most suitable vaccine needs to be determined according to the local epidemiology of Hib disease. Commercial combination vaccines may lead to lower antibody levels. A recent increase in the incidence of Hib disease in the UK highlights the importance of continued surveillance and the need for booster vaccinations to ensure continued protection. Conjugate vaccines to Streptococcus pneumoniae and Neisseria meningitidis have been developed. The introduction of a pneumococcal conjugate vaccine in the US has led to a decrease in the rate of infection by nearly 60% in children <5 years of age. A reduction in pneumococcal carriage may also modify disease epidemiology. The UK introduced the conjugate meningococcal C vaccine into its infant schedule with a corresponding reduction in N. meningitidis group C disease. A recent decrease in the effectiveness of the vaccine, however, suggests a booster may be necessary in the future. Our present understanding of the immunology of conjugate vaccines is far from complete. Developed countries have introduced conjugate vaccines into their immunisation schedules to prevent bacterial meningitis; however, their high cost precludes their use in many developing countries. Progress needs to be made in order to get these highly effective vaccines to those areas that need them.