Meningitis B Vaccine Side Effects: What to Expect from Bexsero
Medically reviewed by The Online GP by The Wellness Medical Team — Last updated: 21 March 2026
The meningitis B vaccine (Bexsero) is safe and well tolerated, with over five million doses administered in the UK since 2015 and no major safety concerns identified. The most common side effects are injection-site pain (87–92% of recipients), fatigue (45–49%), headache (37–41%), and nausea (11–13%). These are overwhelmingly mild and resolve within 24–48 hours. Serious adverse reactions are extremely rare, occurring in fewer than 0.01% of doses. This guide covers exactly what to expect after vaccination for adults, teenagers, and babies, and when you should contact a doctor.
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Common Side Effects in Adults and Teenagers
Clinical trials involving over 2,600 adolescents and adults, including 974 university students aged 18–24, provide robust safety data for this age group. The following side effects were reported at rates of 10% or higher and are considered common, expected responses to vaccination. Pain at the injection site is the most frequently reported effect, occurring in 87–92% of trial participants. It typically peaks within hours of vaccination and resolves within a day or two. The pain is usually mild — comparable to a light bruise — and does not prevent normal activity. Applying a cool compress and taking paracetamol or ibuprofen can help if it is bothersome. Fatigue was reported by 45–49% of participants.
This is a general feeling of tiredness rather than debilitating exhaustion. It is part of the normal immune response and typically passes within 24 hours. Rest, hydration, and a light schedule on the day of vaccination are sensible precautions. Headache affected 37–41% of participants. It is usually mild to moderate and responds well to standard over-the-counter pain relief. If you are prone to migraines, discuss this with your doctor before vaccination, though there is no evidence that Bexsero triggers migraines specifically.
Nausea was reported by 11–13% of participants. This is generally mild and short-lived. Eating a light meal before your vaccination appointment may help reduce the likelihood of nausea. Muscle pain (myalgia) affected 10–14% of participants, typically in the arm where the injection was given but occasionally more widespread. It is mild, resolves within a day or two, and responds to paracetamol or ibuprofen. Redness and swelling at the injection site occurred in 10–15% of participants. A small area of redness and mild swelling around the injection point is a normal immune response. It usually resolves within two to three days. A cool compress can provide relief.
Side Effects in Babies and Young Children
Babies experience the same injection-site reactions as older age groups, but with the addition of a higher rate of fever. This is the most important difference for parents to understand. Fever is more common when Bexsero is given alongside other routine childhood vaccines (such as the 6-in-1 and PCV) than when it is given alone. This is a well-studied effect, and the NHS specifically recommends giving infant paracetamol at the time of MenB vaccination to manage it. The recommended dose is 2.5ml of infant paracetamol suspension (120mg/5ml) given at the time of vaccination, with a second dose 4–6 hours later, and a third dose if needed. Paracetamol does not reduce the effectiveness of the vaccine. Irritability is common in babies after vaccination. Your baby may be more unsettled than usual, cry more, and be harder to comfort. This typically resolves within a day. Reduced appetite is normal for 24–48 hours after vaccination. Continue to offer feeds as usual — your baby will return to normal feeding patterns as the immune response settles. Tenderness at the injection site may make your baby reluctant to move the leg where the injection was given (Bexsero is given in the thigh for babies). Gentle handling and avoiding pressure on the injection site will help.
Uncommon and Rare Side Effects
These occur in a small minority of recipients and are documented for completeness. Uncommon side effects (affecting between 1 in 100 and 1 in 1,000 recipients) include a raised, hard lump at the injection site, mild fever in adults and teenagers, and a general feeling of being unwell. These resolve without treatment. Rare side effects (affecting fewer than 1 in 1,000 recipients) include allergic reactions such as skin rash or hives and, very rarely, signs of meningeal irritation (mild, transient neck stiffness or photosensitivity). These signs are an immune response, not meningitis — Bexsero cannot cause meningitis as it contains no living bacteria. Very rare side effects (fewer than 1 in 10,000) include anaphylaxis, which is a severe allergic reaction occurring within minutes of vaccination. This is why all vaccination providers are required to monitor you for at least 15 minutes after injection and have emergency treatment immediately available. At The Online GP by The Wellness, every vaccination is administered by a GMC-registered doctor with full resuscitation equipment on site.
When to Seek Medical Advice After Vaccination
Most side effects are mild and self-limiting. However, you should contact a doctor if injection-site pain, redness, or swelling worsens after 48 hours rather than improving, if fever in a baby exceeds 39°C despite paracetamol, if your baby becomes unusually floppy, unresponsive, or develops a high-pitched cry, if you develop a widespread rash, facial swelling, or difficulty breathing (signs of an allergic reaction — call 999 immediately), or if any side effect is unusually severe or persists beyond 72 hours. For non-emergency advice, The Online GP by The Wellness offers same-day GP consultations from £49 (phone) or £79 (in-person at our Marylebone clinic). Our GMC-registered doctors can assess any post-vaccination concerns and provide reassurance or treatment as needed.
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Putting Side Effects in Context: Risk vs Benefit
Understanding side effects is important for informed consent, but it is equally important to weigh them against the disease the vaccine prevents. Meningococcal group B disease has a case fatality rate of 8–15%. Up to 20% of survivors suffer permanent disabilities including brain damage, hearing loss, limb amputations, and kidney damage. The disease can kill within 24 hours. In the UK, 378 cases were confirmed in 2024–25, with 31 deaths. The 2026 Kent outbreak reached 27 cases in under a week, with 2 deaths and multiple young people in intensive care. By contrast, Bexsero side effects are overwhelmingly mild (injection-site pain, fatigue, headache) and resolve within 24–48 hours. Serious adverse reactions occur in fewer than 0.01% of doses. The risk-benefit calculation is clear: a day or two of mild discomfort in exchange for protection against a rare but devastating disease with an 88% strain coverage rate. This is why public health authorities recommend the vaccine and why the NHS includes it in the routine childhood schedule.
Why Doctor-Led Vaccination Provides Extra Reassurance
At The Online GP by The Wellness, every vaccination is administered by a GMC-registered doctor, not a pharmacist or nurse. This means a full medical history review before vaccination to identify any contraindications, personalised advice on managing side effects based on your medical profile, immediate access to a doctor if you experience an adverse reaction, prescribed medication if needed (for example, antihistamines for an allergic reaction, which a pharmacist cannot prescribe on the spot), and 15 minutes of monitored observation in a calm clinical environment. Our Marylebone clinic provides a private, unhurried setting — a meaningful difference from the pharmacy counter for anyone who is anxious about vaccination or who has a complex medical history. We are currently operating a waiting list for MenB vaccination due to the national shortage, with pricing from £495 per dose (reflecting elevated procurement costs of £300–400+ per dose during the shortage). MenACWY and other vaccines may be available immediately.
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Frequently Asked Questions
What are the common side effects of the MenB vaccine? Injection-site pain (87–92%), fatigue (45–49%), headache (37–41%), nausea (11–13%), muscle pain (10–14%), and redness/swelling (10–15%). All typically mild and resolving within 24–48 hours.
Is Bexsero safe? Yes. Over 5 million doses given in the UK since 2015 with no major safety concerns. Serious reactions occur in fewer than 0.01% of doses. It is not a live vaccine and cannot cause meningitis.
How long do side effects last? Most resolve within 24–48 hours. Injection-site tenderness may persist for up to 3 days. Contact a doctor if symptoms worsen after 48 hours or persist beyond 72 hours.
Should I give my baby paracetamol? Yes — NHS-recommended. Give 2.5ml of infant paracetamol (120mg/5ml) at the time of vaccination, then every 4–6 hours as needed. This does not reduce vaccine effectiveness.
Can Bexsero cause meningitis? No. It contains no living bacteria. Very rarely, mild transient neck stiffness can occur as an immune response, but this is not meningitis and resolves quickly.
Are side effects worse after the second dose? Generally similar to the first dose. Some people report slightly more injection-site soreness. Serious reactions are no more common after the second dose.
Can I have an allergic reaction? Anaphylaxis is extremely rare (fewer than 1 in 100,000 doses). All providers must monitor you for 15 minutes and have emergency equipment available. At The Online GP by The Wellness, a doctor is present throughout.
The Online GP by The Wellness provides private doctor-led healthcare from our Marylebone clinic. Contact us on WhatsApp at +44 7961 280835 or email team@thewellnesslondon.com.This article is for informational purposes only. If you suspect meningitis symptoms, call 999 immediately.
References
GSK. Bexsero Summary of Product Characteristics. Electronic Medicines Compendium. 2025.
European Medicines Agency. Bexsero EPAR. Updated 2025.
UKHSA. Cases of invasive meningococcal disease confirmed in Kent. GOV.UK. Updated 21 March 2026.
Meningitis Now. FAQs on the MenB vaccine (Bexsero). Updated 2026.
NHS. MenB vaccine side effects. NHS.uk. Updated 2025.
FDA. Bexsero prescribing information — clinical trial safety data. 2024.
