Health condition
Terminal complement and meningococcus
Deficiency of the terminal complement components C5-C9 - or of properdin - specifically disables the body's meningococcus-killing weapon, raising lifetime risk of meningococcal disease several-thousand-fold in some series; vaccination and rapid-access antibiotics rewrite that risk.
Why trust this guide
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Editorial team
Written by our editorial team from the UK sources listed on each page.
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Sourced from guidance
Checked against current NHS and UK specialist society guidance at the time of review.
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Current for 2026
Reviewed on 2026-09-27 with the next review scheduled for 2027-09-27.
Key facts
The essentials at a glance.
The symptoms to recognise, when to seek help, which specialist to see, and what treatment usually involves.
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The membrane-attack complex (C5b-9) is the principal defence against neisseria; without it, meningococcal disease recurs and often involves unusual serogroups (W, X, Y, E)
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Curious silver lining: disease in deficient patients is often less severe - but never reliable enough to relax about
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Screen after any second meningococcal episode, any unusual-serogroup case, or a family history: CH50/AP50 first, then component levels
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Protection: full ACWY and MenB vaccination with boosters, immediate-access 'rescue' antibiotics, and prophylaxis in some cases
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The same vulnerability applies to patients on complement-blocking drugs (eculizumab and relatives) - identical precautions apply
Understanding the condition
What it is and what happens next.
What causes it, how it is diagnosed, and the treatment routes available in the UK.
What it is and how it feels
Meningococcus is unusual among bacteria in being killed principally by complement's final act - the membrane-attack complex drilling through its outer wall. People missing any terminal component conduct most of immunity normally, then meet this one organism repeatedly: series report risks thousands of times baseline, episodes recurring across decades, and serogroups rarely seen in the general population. Properdin deficiency, an X-linked stabiliser defect, produces a similar and sometimes fulminant vulnerability in males. Most affected people have no idea until the second episode - if testing happens even then.
Diagnosis and treatment routes
The protective playbook is concrete: quadrivalent ACWY and MenB vaccination with scheduled boosters (responses remain useful because antibody enables other killing routes), a standing supply of emergency antibiotics with clear instructions to use them and attend hospital at the first suggestive symptoms, medical alert documentation, and screening of siblings and children. Anyone who has had meningococcal disease twice - or once with an odd serogroup - should not leave the system without complement testing; a private immunology appointment is typically available within about two weeks.
Seeing a specialist
Who to see, and how quickly you can be seen.
The specialist for this condition is usually a consultant clinical immunologist. Your GP can refer you on the NHS, or you can arrange a private consultation directly.
A quiet reminder
This guide is for information, not medical advice.
Your GP knows your history and can tell you which parts apply to you. If in doubt, see them - and seek urgent care for any of the emergency symptoms described above.
Frequently asked
Common questions about Terminal complement and meningococcus.
Quick, plain-English answers to what people ask us most.
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What does terminal complement and meningococcus mean?
Terminal complement and meningococcus is an infection caused by a specific organism (bacteria, parasite, fungus or virus depending on the condition). It can range from mild and self-limiting to serious, particularly in people who are unwell, very young, elderly, or immunocompromised.
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What are the risk factors for terminal complement and meningococcus?
It is caused by exposure to the specific organism responsible, and risk is higher with certain exposures, close contact, travel history, or a weakened immune system. Good hygiene, appropriate precautions, and prompt treatment reduce complications.
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What are the symptoms of terminal complement and meningococcus?
Symptoms depend on the organism and site involved but often include fever, localised pain or swelling, and general unwellness. Severity can range from mild to serious, so it's worth seeking medical advice if symptoms are significant or not improving.
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Is terminal complement and meningococcus serious or dangerous?
Severity ranges from mild and self-limiting to potentially serious, particularly if untreated, in very young or elderly people, or in those with a weakened immune system. Prompt assessment and appropriate treatment reduce the risk of complications.
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Is terminal complement and meningococcus something that runs in families?
In most cases this isn't primarily hereditary, though family history and shared lifestyle or environmental factors can sometimes play a role in overall risk. If you're concerned about a family pattern, mention it to your doctor so they can consider it in your assessment.
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Can terminal complement and meningococcus be cured, reversed or prevented?
Most infections of this kind can be treated effectively with appropriate medical therapy, and prevention often relies on hygiene measures, avoiding known exposures, and in some cases vaccination or prophylaxis.
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What treatment options are available for terminal complement and meningococcus?
Treatment typically involves targeted antimicrobial therapy appropriate to the organism involved, alongside supportive care, with the specific choice guided by test results and severity.
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How long does terminal complement and meningococcus last, or take to recover from?
Many infections resolve within days to a few weeks with appropriate treatment, though this depends on the organism, severity, and your overall health — your clinician can give you a more specific estimate.
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When should specialist referral be considered for terminal complement and meningococcus?
Specialist input is worth seeking if symptoms are severe, not improving with initial treatment, or if you are in a higher-risk group (very young, elderly, pregnant, or immunocompromised).
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When should I see a doctor about terminal complement and meningococcus, and how quickly can I be seen privately?
See a doctor if symptoms are persistent, worsening, or affecting your daily life — earlier assessment generally leads to better management. NHS routine referrals for this kind of concern often take 20–45 weeks or longer depending on the area, while a private consultant can typically see you within about 2 weeks, with faster access to scans and specialist opinion.