Bexsero is a vaccine that protects against meningococcal group B disease, a bacterial infection that can cause life-threatening meningitis and bloodstream infections. It is approved by the FDA for people ages 10 through 25 and is one of only two vaccines available that target serogroup B, one of the three serogroups responsible for most meningococcal disease in the United States.
What Bexsero Protects Against
Meningococcal disease is caused by a bacterium called Neisseria meningitidis. It takes two main forms: meningitis, where bacteria infect the lining of the brain and spinal cord and cause swelling, and bloodstream infection (septicemia), where bacteria enter the blood and damage blood vessel walls, leading to bleeding in the skin and organs. The disease can be fatal within hours of the first symptoms appearing.
Several serogroups of the bacterium exist, and serogroups B, C, and Y cause most cases in the U.S. Older meningococcal vaccines (the MenACWY shots often given around age 11) cover groups A, C, W, and Y but leave group B unaddressed. Bexsero fills that gap.
How the Vaccine Works
Bexsero contains four proteins found on the surface of group B meningococcal bacteria. When injected, these proteins teach the immune system to recognize the bacterium as a threat and produce antibodies against it. If the vaccinated person later encounters the real bacterium, those antibodies, along with other parts of the immune system, can kill it before it causes disease.
The proteins are attached to an aluminum-containing compound that acts as an adjuvant, boosting the immune response so the body mounts a stronger defense than it would from the proteins alone.
Who Should Get It
In the U.S., the FDA has approved Bexsero for individuals ages 10 through 25. The CDC recommends it as a shared clinical decision for teens and young adults ages 16 through 23, meaning you and your doctor decide together whether the vaccine makes sense for you. For people at increased risk of meningococcal B disease, vaccination is more strongly recommended regardless of age within the approved range.
Higher-risk groups include people with certain complement deficiencies (part of the immune system that helps kill bacteria) and those taking medications that block a specific step in that immune pathway. These individuals remain at elevated risk for invasive meningococcal disease even after vaccination, so additional precautions may still apply.
In countries like the United Kingdom, Bexsero is part of the routine infant immunization schedule, given as early as two months of age.
Dosing Schedule
For adolescents and young adults in the U.S., Bexsero is given as a two-dose series. Both doses are injected into the muscle, typically the upper arm. People at increased risk for meningococcal B disease may need additional doses. Importantly, the two available serogroup B vaccines, Bexsero and Trumenba, are not interchangeable. If you start with Bexsero, both doses must be Bexsero.
Common Side Effects
Injection site pain is the most frequently reported side effect. In clinical trials, up to 90% of recipients experienced some degree of pain at the injection site, and 20 to 29% rated that pain as severe. Other common reactions include muscle aches, fatigue, headache, nausea, and general feelings of being unwell. Fever occurs less often, though many people take over-the-counter pain relievers after vaccination, which may mask mild fevers.
Post-market safety monitoring from 2015 to 2018 found a similar pattern: injection site pain (22%), fever (16%), headache (16%), redness at the injection site (15%), and arm pain (15%) were the most commonly reported events. These side effects are generally short-lived, resolving within a day or two.
Managing Fever in Infants
In countries where infants receive Bexsero, health authorities recommend giving infant acetaminophen (paracetamol) at the time of vaccination rather than waiting for a fever to develop. The UK guidance calls for three doses of liquid acetaminophen: one at the time of the shot, a second four to six hours later, and a third four to six hours after that. This preventive approach reduces the chance of post-vaccination fever. Notably, this precaution is not routinely needed after the 12-month booster dose.
How Well It Works
The UK became the first country to add Bexsero to its national infant immunization program in 2015, providing the clearest picture of real-world effectiveness. A national study published in The Lancet found that cases of meningococcal B disease among vaccine-eligible infants dropped by 50% in the first 10 months of the program. That reduction held regardless of whether individual infants had been vaccinated, suggesting the vaccine also reduced bacterial transmission within the population.
How Long Protection Lasts
Antibody levels decline over time after the initial two-dose series in adolescents and young adults. A study tracking recipients for up to 7.5 years found that protective antibody levels varied widely depending on which of the four vaccine proteins was measured. Against some antigens, as many as 84% of vaccinated people still had protective levels years later, while against others, that figure dropped as low as 9%.
Even when antibody levels fell, vaccinated individuals retained higher levels than people who were never vaccinated. More importantly, a single booster dose rapidly restored protection: within one month, 93 to 100% of previously vaccinated people had protective antibody levels against all four antigens. The immune system responded faster and more strongly to the booster than it did to a first dose in unvaccinated people, confirming that the original series creates lasting immune memory even as circulating antibodies fade.
Bexsero vs. Trumenba
Trumenba is the other serogroup B meningococcal vaccine available in the U.S. The key differences are in composition and dosing. Bexsero contains four bacterial surface proteins plus outer membrane vesicles, giving it a broader antigenic profile. Trumenba targets a single protein (fHbp) but includes two variants of it.
For people not at increased risk, both vaccines involve two doses. For those at higher risk, Trumenba requires three doses while Bexsero remains at two. Both vaccines are considered effective, and the choice between them often comes down to availability and scheduling preferences. The critical rule is to complete your series with the same brand you started with.