What are Meningococcal Bacteria?

Meningococcal bacteria are gram-negative diplococci bacteria that can cause severe infections such as meningitis, which is an inflammation of the membranes surrounding the brain and spinal cord, or sepsis, which is an infection in the bloodstream. There are several serogroups of the Neisseria meningitidis bacteria that can cause disease, including serogroups A, B, C, W, X and Y. However, serogroups B and C are responsible for most cases of meningococcal disease globally. Meningococcal infections can progress very rapidly and may cause death or permanent disability such as hearing loss, neurological damage or loss of limbs within hours. While meningococcal disease can affect people of all ages, it predominately affects infants, children and teenagers/young adults.

Vaccines Against Serogroups A, C, W and Y

To help prevent diseases caused by different serogroups of meningococcal bacteria, several vaccines have been developed and are included in national immunization programs worldwide. Vaccines are available that protect against four of the main disease-causing serogroups: A, C, W, and Y. The first vaccine targeting serogroup C was licensed in 1999 and was introduced into many national immunization schedules globally. More recently, vaccines that protect against serogroups A, W and Y have also been added to immunization schedules in certain regions. For example, the quadrivalent ACWY vaccine protects against all four of these serogroups with a single vaccine. Routine immunization of adolescents/young adults with the ACWY vaccine is now recommended in many countries given that this age group has the highest rates of meningococcal disease. ACWY vaccines provide both individual protection to vaccinated individuals as well as indirect herd protection to unvaccinated individuals in the community by reducing transmission.

Challenges with Meningococcal Vaccines

Meningococcal Vaccines While effective vaccines exist for serogroups A, C, W and Y, the development of a vaccine for serogroup B has proven more challenging. This is because the serogroup B capsular polysaccharide is similar to polysaccharides contained in human brain and nerve cells. As a result, the immune system does not mount a strong immune response against this polysaccharide in the same way it does against polysaccharides in other serogroups. However, newer protein-based vaccines using subcapsular components of serogroup B have been developed since the late 2000s. These 4CMenB vaccines provide broad coverage against diverse disease-causing strains expressing different protein variants. New adjuvanted versions of 4CMenB vaccines also induce stronger immune responses, especially in young infants. Following clinical trials demonstrating their safety and effectiveness, 4CMenB vaccines have been introduced into national childhood immunization programs in several developed countries experiencing higher rates of serogroup B disease. This includes countries like the UK, Canada, Spain and New Zealand. While these vaccines prevent over 80% of serogroup B strains occurring in these countries, ongoing surveillance is required to monitor effectiveness and ensure the vaccines cover emerging strains. Development of a low-cost, universally effective serogroup B vaccine suitable for broad global usage remains an ongoing challenge.

Recommended Vaccination Schedules

The recommended age at which individuals receive vaccines against different meningococcal serogroups varies according to a country's national immunization schedule and epidemiological context. In many western countries, infants are the main group targeted for vaccination against serogroup B and C disease because incidence is highest in this age group. Most national schedules now recommend administration of 1 or 2 routine doses of 4CMenB vaccines at 2, 4 and 12 months of age, in a 2+1 or 3+0 schedule. For protection against serogroups A, C, W, and Y, a routine dose of the quadrivalent ACWY conjugate vaccine is recommended at 12-15 months of age, with a booster dose at 12-18 years of age targeting adolescents and young adults. This is the age group accounting for the highest burden of these serogroups globally. Additionally, certain high-risk groups such as those with complement deficiencies, asplenia and microbiologists may be recommended booster doses of meningococcal vaccines throughout their lives. Immunocompromised individuals receiving stem cell transplants also may receive quadrivalent conjugate vaccines prior to transplantation. Overall, countries are working to expand access to effective meningococcal vaccines to protect high-risk populations and reduce the transmission of this potentially fatal disease.



while meningococcal disease remains an important global public health issue, the development of protein-based vaccines against serogroup B as well as conjugate vaccines targeting common disease-causing serogroups including A, C, W and Y has significantly expanded options for prevention. Countries are working to introduce these new generation vaccines into childhood immunization programs according to local epidemiological needs. As vaccination coverage increases globally, invasive meningococcal disease has dramatically declined in several nations. Continued surveillance is essential to monitor vaccine effectiveness against evolving meningococcal strains and ensure lifelong protection of high-risk groups. With ongoing access to safe and effective vaccines, the aim is to eliminate meningococcal disease as a major public health threat worldwide.

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