Ask the Experts: Meningococcal ACWY: Disease Issues

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Meningococcal disease is a bacterial infection caused by Neisseria meningitidis. Meningococcal disease usually presents clinically as meningitis (about 50% of cases), bacteremia (30% of cases), or bacteremic pneumonia (15% of cases). N. meningitidis colonizes mucosal surfaces of the nasopharynx and is transmitted through direct contact with large-droplet respiratory tract secretions from patients or asymptomatic carriers. Meningococcal disease can be severe. The overall case-fatality ratio in the U.S. is 15%, and 10%–20% of survivors have long-term sequelae such as neurologic disability, limb or digit loss, and hearing loss.

N. meningitidis is classified into 12 serogroups based on characteristics of the polysaccharide capsule. Most invasive disease (such as meningitis and sepsis) is caused by serogroups A, B, C, W, X and Y. The relative importance of serogroups depends on geographic location and other factors such as age. Between 2011 and 2020 in the United States, serogroup B caused about 60% of cases among children younger than 5 years old, and serogroups C, W, or Y caused about two out of three cases in people age 11 years or older. Serogroup A is rare in the U.S. Historically, serogroup A was common in the meningitis belt of sub-Saharan Africa, but after the implementation of a meningococcal serogroup A conjugate vaccine campaign, serogroup A disease has been nearly eliminated in the meningitis belt.

Nasopharyngeal carriage rates are highest in adolescents and young adults who serve as reservoirs for transmission of N. meningitidis.

Last reviewed: March 24, 2024

The incidence of meningococcal disease has declined steadily in the U.S. since a peak of reported disease in the late 1990s. Even before routine use of a meningococcal conjugate vaccine against serogroups A, C, W, and Y (MenACWY) was recommended for adolescents in 2005, the overall annual incidence of meningococcal disease had decreased 64%, from 1.1 cases per 100,000 population in 1996 to 0.4 cases per 100,000 population in 2005. In 2021, the rate of meningococcal disease in the United States reached a historic low of 0.06 cases per 100,000 population.

In 2021, the most recent CDC surveillance final report stated that, of U.S. cases with known serogroup, 46 cases were serogroup B (incidence rate of 0.01 cases per 100,000, or 1 case per 10 million population) and 108 cases were serogroups C, Y, or W. The incidence of disease is extremely low in all age groups, but is highest in infants under 1 year (0.56 cases per 100,000), children age 1 through 4 years (0.10 cases per 100,000). Among adolescents age 16–23, the incidence rate was 0.05 cases per 100,000 population, which equals 5 cases per 10 million people age 16–23 in 2021. In total, 209 cases of meningococcal disease were reported in the United States in 2021.

Rates of meningococcal disease in the United States increased in 2023. Much of this increase was due to a sharp increase in serogroup Y disease. In 2023, 415 confirmed and probable meningococcal disease cases were reported in the United States (preliminary data), which is similar to the rate in 2014. People disproportionately affected by the increase include Black people between the ages of 30 and 60 years, and adults with HIV. Adults with HIV are routinely recommended to be vaccinated against meningococcal serogroups A, C, W, and Y.

Last reviewed: March 24, 2024

In addition to risk based on age, non-specific risk factors for serogroups A, C, W and Y include having a previous viral infection, living in a crowded household, having an underlying chronic illness, and being exposed to cigarette smoke (either directly or second-hand).

The following groups are at increased risk for all meningococcal serogroups:

  • People with persistent (genetic) complement component deficiencies (a type of immune system disorder)
  • People who use complement inhibitors such as eculizumab (Soliris, Alexion Pharmaceuticals) and ravulizumab (Ultomiris, Alexion Pharmaceuticals) for treatment of atypical hemolytic uremic syndrome or paroxysmal nocturnal hemoglobinuria
  • People with anatomic or functional asplenia
  • Microbiologists routinely exposed to meningococcal isolates in a laboratory
  • People at increased risk during an outbreak of meningococcal disease
  • Military recruits
  • College students

Certain groups are at increased risk of serogroups A, C, W and Y, but not serogroup B:

  • People living with HIV
  • Men who have sex with men (MSM)
  • Travelers to countries where meningococcal disease is endemic or hyperendemic, such as the meningitis belt of sub-Saharan Africa
Last reviewed: March 24, 2024

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