Neisseria meningitidis (Nm), also known as meningococcus, is an encapsulated Gram-negative diplococcus that can be found intra- or extracellularly in the blood in polymorphonuclear leukocytes. Due to differences in composition, there are 13 meningococcal serogroups; six serotypes (A, B, C, W, Y, and X) are usually associated with disease.

Key facts

In Latin America, the real burden of meningococcal disease is underestimated in most countries today. For example, a literature review found very different incidence rates in the period 2008-2011, ranging from less than 0.1 to 1.8 per 100,000 inhabitants, depending on the country and year. These rates represent low endemicity (<2 cases per 100,000) and are below the high-risk threshold for vaccine recommendation in national immunization programs or for outbreak control, according to WHO. However, these rates should be interpreted carefully: the challenges to reporting the disease in the Region may partially explain the differences in incidence.
The incidence of invasive meningococcal disease (IMD) is highest in children under 1 year of age and remains relatively high until about age 5. Despite a declining trend in older children, it increases again in adolescents and young adults, especially when they are living together. Incidence decreases again in adults.
IMD causes significant morbidity and mortality, with a case-fatality rate of 10-15% (and up to 40% for meningococcemia). In Latin America, it is estimated that one in five IMD patients die.
Up to 20% of IMD survivors can have permanent sequelae; sensorineural hearing loss is the most common. Other important sequelae include speech disorders, mental retardation, motor abnormalities, seizures, visual disorders, and loss of an arm or leg in cases of meningococcemia.

Fact sheet

> Invasive Meningococcal Disease (IMD)

Meningococcus can invade and infect different sterile spaces in the human body, but the most serious infections are meningitis and meningococcal disease. Meningitis is the most common clinical presentation.

Meningitis is an inflammation of the membranes that line the brain, cerebellum, and bone marrow, anatomical sites surrounded by subarachnoid space through which cerebrospinal fluid circulates. Meningococcemia is a rare form of infection that occurs when it spreads through the bloodstream (i.e., sepsis) with or without meningitis. What begins as an erythematous and macular rash rapidly becomes petechia and, eventually, ecchymosis.

Meningitis and meningococcemia can rapidly lead to stupor, coma, and death.

> Transmission

Meningococcus is transmitted by direct contact (person to person) or by contact with nasopharyngeal secretions (droplets) of an infected person. This usually occurs during close contact such as coughing, sneezing, kissing, or long-term contact such as living in close proximity to others.

> Carrier status

Meningococcus can colonize the human oropharynx, dangerously causing carrier status. It can be passed on to someone else as it progresses to an invasive disease resulting in meningitis, septicemia/meningococcemia, or both. The highest prevalence of carriers with meningococcus in the nasopharynx is among adolescents and young adults; it is less common in young children and adults.

> People at risk

Susceptibility to meningococcal infection is universal: everyone is susceptible to infections caused by this bacterium. However, some conditions increase susceptibility: overcrowding, active or passive exposure to tobacco smoke, and concurrent upper respiratory infections. People with certain chronic diseases are at increased risk of invasive meningococcal infection.

Distribution and seasonality

The distribution of invasive meningococcal disease is highly specific; there are regional variations in serogroups, peak season, and incidence. Regarding seasonality, in Europe and the United States the highest incidence of cases is observed during the winter and spring. In sub-Saharan Africa, cases usually increase during the dry season.

Prevalence of meningococcal serogroups

Globally, serogroup A used to be the most common causal agent of invasive disease in infants under 1 year old, and the geographical area most affected by this serogroup was sub-Saharan Africa (African belt). Serogroup A has circulated in the Region of the Americas (North America and Latin America) and the Caribbean for the last 65 years. However, serogroup A has decreased in the African belt due to the introduction of the vaccine. Most cases of serogroups B and C occur in Europe and the Americas, while serogroups A and C are the most common cause of IMD in Asia. Since the mid-1990s, there have been increases in IMD caused by serogroup Y in the United States and Israel, while serogroup X has caused local epidemics in sub-Saharan Africa. In addition, a growing proportion of cases of serogroup W infection has been identified.

> Immunity

Immunity can be acquired passively via the placenta or actively through prior infection or immunization. The immune response to clinical and subclinical infections is of unknown duration. There is a different immune response to each of the three types of available vaccines: polysaccharides, conjugates, and recombinants.

Polysaccharide vaccines have limitations: they do not induce an immune response in children under 2 years of age, have little effect on carriers, result in a decreased level of protection within a few years, and do not generate a memory response. Conjugate vaccines produce a good and long-lasting antibody seroconversion response, including in children under age 2, by inducing immunological memory. In addition to inducing immunological memory and secondary humoral responses, they have been shown to produce herd immunity by reducing bacterial colonization of the respiratory tract in vaccinated people, thus reducing transmission to third parties, including adults. Recombinant meningococcal B vaccines produce long-term individual protection. To date, there has been no demonstrated effect on carriers.

WHO position papers on Meningococcal vaccine

Prevention and control - Meningococcal vaccines

There are several types of vaccines to control invasive meningococcal disease:

There are several types of vaccines to control invasive meningococcal disease: Meningococcal polysaccharide vaccines (A, C, W, Y)
Meningococcal conjugate vaccines: monovalent (A and C) and quadrivalent (A, C, W, Y)
Recombinant meningococcal B vaccines
Outer membrane vesicle (OMV) vaccines or serogroup B proteoliposome vaccines associated with serogroup C polysaccharides The first available vaccines were polysaccharides.

These vaccines have played an important role in the control of outbreaks and epidemics and are still used for this purpose. However, due to their limitations, they are gradually being replaced by conjugate vaccines.

Since 1999, meningococcal C conjugate vaccines have been available and widely used. A tetravalent meningococcal conjugate vaccine (groups A, C, W, and Y) for children and adults were introduced in the United States of America, Canada, and Europe in 2005. As of June 2015, more than 220 million people between the age of 1 and 29 had received the meningococcal A conjugate vaccine in 16 countries in the "African meningitis belt".

The meningococcal B outer membrane vesicle vaccine associated with serogroup C polysaccharides has been used in Cuba since 1989. In 1991, it was included in the Cuban national immunization program, where it continues to be used. Two recombinant meningococcal B vaccines are available: one with four antigens (fusion and membrane proteins) and one with two antigens. Recombinant vaccines have been on the market since 2013.

The decision to introduce a meningococcal vaccine, which age groups of the population will be included, and which vaccine to choose depends on the epidemiological situation in each country.

As of December 2020, four Latin American countries have included a conjugated meningococcal vaccine in their routine vaccination schedules: Argentina (for groups A, C, W, and Y), Brazil (for serogroup C and for serogroups A, C, W, and Y), Chile (for serogroups A, C, W, and Y), and Cuba (meningococcal B outer membrane vesicle vaccine associated with serogroup C polysaccharides).

Recommendations of the Technical Advisory Group

Recommendations of the Technical Advisory Group on Vaccine-preventable Diseases (TAG) on available meningococcal vaccines (2017 meeting in Panama City):

The TAG urges countries to expand their surveillance of bacterial meningitis from sentinel to national (universal) surveillance in order to better understand the epidemiology of the disease and its burden. This will support decision-making on the introduction of the meningococcal vaccine and will facilitate timely detection of outbreaks.
Countries should review the epidemiology of the disease when assessing the possible introduction of the meningococcal vaccine. This includes the occurrence of outbreaks; age distribution and serogroups; the burden and costs of the disease; the effectiveness of the vaccine; its safety, price, and duration of protection; and the logistical and operational aspects of the immunization program.
In order to improve the results of cost-effectiveness studies, it is recommended to include evaluations of the long-term sequelae of meningococcal disease in the assessments.
The TAG reminds countries that studies on carriers provide valuable information on disease transmission but are not essential for deciding on the use of a particular vaccine. It should be noted that such studies tend to be expensive, complex, and difficult to interpret.

Surveillance

PAHO has been coordinating a sentinel surveillance network for pneumonia and bacterial meningitis in the Region of the Americas since 2007. Since 2014, this network has been part of the Global Surveillance Network, led by the World Health Organization. Currently, nine countries and 20 hospitals participate in this network.