Meningococcal B is a type of serious bacterial infection caused by one specific strain of the bacterium Neisseria meningitidis, known as serogroup B. This serogroup is responsible for the majority of meningococcal disease cases in Europe and a significant share in the United States, where roughly 503 total meningococcal cases were reported in 2024. The infection most commonly causes meningitis (inflammation of the membranes surrounding the brain and spinal cord) or septicemia (a dangerous bloodstream infection), and it can become life-threatening within hours.
How Serogroup B Differs From Other Strains
At least 12 serogroups of Neisseria meningitidis exist, but serogroups A, B, C, W, X, and Y cause the vast majority of infections. Each serogroup is defined by the structure of its outer capsule, a sugar-based coating the bacterium uses to evade the immune system. Serogroup B’s capsule is chemically similar to molecules found on human nerve cells, which historically made it difficult to develop a vaccine against it. While vaccines for serogroups A, C, W, and Y have been available for decades, serogroup B vaccines only became available in the mid-2010s because scientists had to target different surface proteins instead of the capsule itself.
Most serogroup B disease occurs in young children, though teens and young adults face a notable spike in risk as well.
How It Spreads
The bacteria spread through respiratory secretions: kissing, coughing, sharing drinks, or living in close quarters with someone who carries the bacteria. Importantly, about 5 to 10 percent of people carry meningococcal bacteria in the back of their nose and throat at any given time without ever getting sick. These asymptomatic carriers can still transmit the bacteria to others. Once someone is exposed, disease typically develops within 1 to 10 days.
Symptoms to Recognize
Meningococcal B infection presents as meningitis in about half of U.S. cases. The rest develop bloodstream infection or a combination of both. Symptoms come on fast and can worsen dramatically over just a few hours.
In older children, teens, and adults, the hallmark signs include sudden high fever, severe headache, and a stiff neck. Nausea, vomiting, confusion, sensitivity to light, and seizures can follow. A distinctive skin rash can appear, often starting as tiny red or purple pinpoint spots that don’t fade when you press a glass against them. This rash signals that bacteria are damaging blood vessels and is a medical emergency.
In babies and toddlers, the signs are harder to spot. Parents may notice a high fever, constant crying, unusual sleepiness or irritability, poor feeding, vomiting, or a bulging soft spot on the top of the head. Stiffness in the body and neck can also occur, though infants may simply appear limp or unresponsive rather than visibly stiff.
Who Faces the Highest Risk
Age is the single biggest risk factor. Young children and teenagers through young adults (roughly 16 to 23) are most vulnerable. College freshmen living in dormitories face elevated risk because of close living conditions, as do military recruits in training facilities.
Certain medical conditions significantly raise the odds of infection. People missing a working spleen, whether it was surgically removed or doesn’t function properly (as in sickle cell disease), lose a key defense against encapsulated bacteria like meningococcus. Deficiencies in the complement system, a part of the immune system that helps kill bacteria directly, also create vulnerability. People living with HIV, particularly those with a low CD4 count or high viral load, face increased risk as well. Some medications that suppress part of the complement system also raise susceptibility.
Close contacts of someone with confirmed meningococcal disease, including household members, roommates, and kissing partners, are considered at immediate risk and typically receive preventive antibiotics.
How It Is Diagnosed
Doctors confirm meningococcal B by testing blood or cerebrospinal fluid (the fluid surrounding the brain and spinal cord, collected through a spinal tap). The primary test is a bacterial culture, where a lab grows bacteria from the sample to identify the exact organism. If the culture results are unclear, a PCR test can detect tiny amounts of the bacteria’s genetic material, or an antigen test can look for specific bacterial proteins. These tests also identify the serogroup, confirming whether serogroup B is responsible.
Treatment and Prognosis
Meningococcal B disease is treated with intravenous antibiotics in a hospital, and treatment needs to start as quickly as possible. Even with appropriate therapy, 5 to 10 percent of patients die within 24 to 48 hours of developing symptoms. European data shows serogroup B specifically carries a case fatality rate of about 8 percent.
Among those who survive, 10 to 20 percent experience long-term complications. These can include hearing loss, neurological damage, skin scarring, and in severe cases, amputation of fingers, toes, or limbs due to tissue damage from the bloodstream infection. Children tend to face higher rates of amputation and scarring than adults. In one Canadian study, amputations occurred in about 7.6 percent of children compared to 3.1 percent of adults with invasive disease. Skin scarring affected roughly 5 percent of all survivors.
Vaccination Against Serogroup B
Two vaccines protect against serogroup B: Bexsero and Trumenba. Both are approved for people 10 years and older. The number of doses depends on your risk level. People aged 16 through 23 who are not at increased risk receive 2 shots, while those 10 and older with conditions like complement deficiency, asplenia, or sickle cell disease receive 3 shots.
The CDC’s recommendation for serogroup B vaccination is nuanced. For high-risk individuals, the vaccine is strongly recommended. For healthy 16- to 23-year-olds, it falls under what the CDC calls “shared clinical decision-making.” This means the vaccine is not routine for everyone in that age group, but it is available, and the decision is meant to be made between you and your healthcare provider based on your individual circumstances. Factors like heading off to college, living in close quarters, or simply wanting extra protection can all be part of that conversation.
This is different from the standard meningococcal ACWY vaccine, which is routinely recommended for all preteens at age 11 or 12 with a booster at 16. The two vaccine types protect against different serogroups, so receiving one does not cover the other.
Preventive Antibiotics for Close Contacts
When someone is diagnosed with meningococcal disease, their close contacts typically receive antibiotics to prevent the bacteria from taking hold. This includes household members, roommates, and anyone who had direct contact with the patient’s oral secretions. The goal is to eliminate any bacteria that may have been transmitted before they cause illness.