What Are the Side Effects of a Meningitis Shot?

Most people who get a meningitis vaccine experience nothing worse than a sore arm and mild fatigue that clear up within a day or two. Across large clinical trials and post-market surveillance involving millions of doses, serious reactions remain rare, and the most commonly reported events are injection-site pain, low-grade fever, and headache. The picture gets more specific depending on which type of meningitis vaccine you receive, how old you are, and whether other shots are given at the same visit.

The Most Common Side Effects

There are two main categories of meningitis vaccine in wide use: the quadrivalent conjugate vaccines that protect against serogroups A, C, W, and Y (often called MenACWY), and the serogroup B vaccines (MenB). Both share a core set of mild, short-lived side effects. Pain, redness, or swelling at the injection site tops the list for both. Headache, muscle aches, and general tiredness are also frequently reported. Low-grade fever rounds out the typical profile.

How often these reactions occur and how noticeable they feel differs between the two vaccine types. In head-to-head comparisons, MenACWY vaccines tend to produce fewer reactions overall than serogroup B vaccines.¹ MenACWY vaccines have been described as having a safety profile comparable to other routine vaccines, with minor adverse events across multiple large trials in children, adolescents, and adults.² The MenB vaccines, while still well tolerated overall, are more likely to trigger fever, especially in infants.

Why MenB Vaccines Tend to Cause More Fever

If your child ran a higher temperature after a MenB shot than after other routine vaccines, there is a biological reason. Researchers have traced the fever response to a specific component of the MenB vaccine called the outer membrane vesicle (OMV). That vesicle contains a form of endotoxin, a molecule the immune system recognizes as a bacterial signal. When the body detects it, a cascade of inflammation kicks off: immune cells ramp up, a signaling molecule called IL-6 rises in the blood, and enzymes that produce prostaglandins activate in brain tissue. Prostaglandins are what actually reset your body’s thermostat upward, producing fever.³

This is essentially the immune system doing exactly what it is designed to do when it encounters bacterial components. The fever is a byproduct of a robust immune response rather than a sign that something has gone wrong. It typically peaks within the first day and resolves within 48 hours. Prophylactic use of acetaminophen (paracetamol) around the time of vaccination is sometimes recommended by pediatricians to blunt the fever without reducing the vaccine’s immune response.

Side Effects in Infants and Young Children

Infants experience a higher rate of fever after MenB vaccination than older children and adults. A comprehensive review of clinical trials and real-world surveillance data confirmed this pattern but found no significant safety concerns beyond the expected fever.⁴ In a case series from one region, infants who presented to medical care after MenB vaccination most commonly showed poor feeding, sleepiness, and irritability alongside fever. About three-quarters of those infants were admitted to the hospital, largely as a precaution because fever in very young infants warrants evaluation to rule out serious bacterial infection.⁵

Those hospital admissions can be alarming for parents, but the underlying cause is that standard clinical protocols for febrile infants require workup regardless of whether a vaccine was recently given. In the vast majority of cases the fever resolves on its own, and the workup comes back negative for infection. If your infant has already had a fever after a previous dose, the chance of fever recurring with the next dose is higher. One analysis of European trials found that fever recurrence was closely tied to how many prior febrile episodes the child had experienced: roughly four in five infants who had fever after dose one went on to have fever again at dose two.⁶

What Happens When Vaccines Are Given at the Same Visit

Meningitis vaccines are often given alongside other shots, especially in adolescents who may receive a Tdap booster or HPV vaccine at the same appointment. Trials evaluating co-administration of MenACWY with Tdap and HPV vaccines in adolescents found no increase in the frequency of side effects and no reduction in immune responses to any of the vaccines.⁷ A separate trial specifically looking at MenACWY-TT given together with Tdap and HPV vaccines in girls and young women also found no safety concerns.⁸

In infants, the picture is slightly more nuanced. The same European trial data that tracked fever recurrence found that giving MenB at the same visit as routine infant vaccines actually changed the side-effect pattern in both directions. Overall fever rates were somewhat lower when the vaccines were given together compared with giving MenB alone, but moderate-to-severe fevers and fevers lasting more than a day were more common with co-administration.⁶ If your infant tends to spike higher fevers, your pediatrician may suggest spacing out the MenB dose from other shots or pre-dosing with acetaminophen.

Side Effects in Adolescents and Young Adults

Most meningitis shots are given to preteens and teenagers, and the side-effect profile in this age group is reassuringly mild. Surveillance data from the U.S. Vaccine Adverse Event Reporting System (VAERS) for MenACWY found that adolescents aged 11 to 18 accounted for about three-quarters of all reports, and the vast majority described non-serious events consistent with what had been seen in clinical trials. Anaphylaxis and fainting were the two most common serious events flagged, though both were rare.⁹

For the MenB vaccines specifically, VAERS surveillance showed a similar pattern. The most commonly reported side effects for one MenB vaccine (Trumenba) were fever, headache, and pain, with serious reports making up only about 2% of all reports.¹⁰ For the other MenB vaccine (Bexsero), injection-site pain, fever, and headache were again the top complaints, and 96% of reports were classified as non-serious. Some recipients reported decreased mobility in the vaccinated arm secondary to swelling or pain.¹¹

A newer pentavalent vaccine covering serogroups A, B, C, W, and Y together has been tested in adolescents and young adults. In a phase 3 trial, side effects were mostly mild or moderate and occurred at similar rates whether or not the participants had previously received a MenACWY vaccine. No one withdrew from the study because of a vaccine-related adverse event.¹²

Fainting After the Shot

Syncope, or fainting, is one of the more dramatic but generally harmless events that can follow any vaccination in teens and young adults. It is not unique to meningitis vaccines and is more about the act of getting an injection than any specific vaccine ingredient. A study tracking syncope after vaccination in adolescents found a rate of about 3 per 10,000 vaccination events. The risk climbed when multiple vaccines were given simultaneously, reaching roughly 10 per 10,000 when three or more shots were administered at one visit. About 15% of fainting episodes resulted in an injury from falling.¹³

For context, the same study found that syncope was actually more common after a routine blood draw than after vaccination, with a rate roughly five times higher following venipuncture. The practical takeaway: if you or your teenager is prone to feeling lightheaded around needles, sit or lie down for 15 minutes after the shot. Most clinics already enforce a brief observation period for adolescents.

Rare and Serious Side Effects

The side effects that generate the most concern, understandably, are the ones that land people in the hospital. These are genuinely uncommon.

Anaphylaxis is a severe allergic reaction that can include throat swelling, difficulty breathing, and a rapid drop in blood pressure. Across all vaccines (not just meningitis vaccines), anaphylaxis occurs at a rate of roughly 1 to 2 per million doses.¹⁴ During emergency MenB vaccination campaigns on two U.S. college campuses, one case of anaphylaxis was reported in a young woman who developed facial and throat swelling about 30 minutes after her first dose. She was treated promptly and recovered quickly, though she had preexisting hives that may have been a contributing factor.¹⁵ This is why vaccination sites keep epinephrine on hand and ask you to wait before leaving.

Guillain-Barré syndrome (GBS) was an early safety concern raised after the introduction of one MenACWY vaccine (Menactra). GBS is a condition in which the immune system attacks peripheral nerves, causing weakness that can progress to temporary paralysis. After extensive review, the estimated attributable risk was found to be no more than about 0.66 cases per million doses.¹⁶ A separate large study following more than 1.4 million MenACWY vaccinations found zero confirmed GBS cases within six weeks of vaccination, and estimated the upper bound of risk at about 1.5 cases per million.¹⁷ A Canadian study covering 1.9 million people vaccinated with a serogroup C conjugate vaccine also found no increase in GBS above background rates.¹⁸ The current scientific consensus is that if any link between meningococcal conjugate vaccines and GBS exists, it is extremely small.

During the same university outbreak response mentioned above, one case of rhabdomyolysis (muscle breakdown) was reported in a 20-year-old man who had lifted weights shortly after his second MenB dose and then developed severe shoulder and back pain with fever. Investigators classified the vaccine as a possible contributing factor, though weightlifting alone can cause rhabdomyolysis. This remains an isolated report rather than a recognized pattern.¹⁵

Pregnancy and Absent Spleens

Data on meningitis vaccination during pregnancy are limited. Most of the available safety information comes from older polysaccharide vaccines rather than the conjugate or recombinant vaccines now in widespread use.¹⁹ One randomized trial of a polysaccharide meningococcal vaccine in pregnant women found the vaccine to be safe for both mothers and infants, with no congenital defects or major neonatal problems observed. Vaccinated mothers also passed protective antibodies to their babies across the placenta and through breast milk.²⁰ Still, because modern conjugate and protein-based vaccines have not been specifically studied in pregnant women, the decision to vaccinate during pregnancy typically hinges on individual risk. If you are at high risk of meningococcal disease (for example, during an outbreak), a provider may recommend vaccination after weighing the limited data.

People who have had their spleen removed or who have a spleen that does not work well are at especially high risk for meningococcal disease, so vaccination is strongly recommended for this group. A trial of MenACWY-TT in children and adolescents who were splenectomized or hyposplenic found that side effects were comparable to those in healthy controls, with no vaccine-related serious events.²¹

How Vaccine Types Have Changed Over Time

If you received a meningitis shot decades ago, you got a polysaccharide vaccine. These older formulations had real drawbacks: they did not work well in young children, they did not create lasting immune memory, and repeated doses could actually make the immune response weaker over time. Since 1999, conjugate vaccines have largely replaced polysaccharide versions for routine use and have overcome most of those limitations.²² The side-effect profiles of the newer conjugate and recombinant vaccines are generally milder and better characterized, thanks to larger and more rigorous pre-licensure trials and robust post-market surveillance systems. So if your memory of a meningitis shot from the 1990s involves feeling noticeably unwell, the experience with current vaccines is likely to be smoother.

When Parents Worry About Side Effects

Concerns about side effects are the single biggest source of meningococcal vaccine hesitancy among parents. In a large survey, about 41% of parents listed potential side effects as their primary concern about MenB vaccines. Yet when presented with the specific mild reactions that are most common, like injection-site redness or a moderate fever, only about 9 to 11% said those reactions would make them less likely to vaccinate their child.²³ The gap between the vague worry about “side effects” and the actual willingness to accept specific, well-defined ones suggests that much of the anxiety is driven by uncertainty rather than by the side effects themselves. Knowing what to expect, and knowing how common each reaction actually is, tends to close that gap.

A practical concern in the same survey: about 16% of parents said an extra injection at a single visit would make them less willing to vaccinate. If your child’s appointment already involves multiple shots, spacing them across visits is a reasonable option to discuss with your pediatrician. Splitting the visits may reduce the chance of moderate fever in infants, as noted earlier, and can make the experience less overwhelming for needle-averse kids and teens alike.