How Vaccines Work
Training the immune system to recognise a pathogen without having to survive the disease first.
Last revised
Key takeaways
- Mechanism: exposure to an antigen, producing memory cells
- Herd immunity threshold, measles: around 95 per cent coverage
- Most useful single change: Take up every vaccine you are offered.
- Commonest mistake: Assuming childhood vaccination covers you for life.
- See a doctor if any of the signs under "When to get help" below apply to you.
Why it matters
It is the only intervention producing specific, durable protection against a named infection.
The numbers, in one place
| Measure | Figure |
|---|---|
| Mechanism | exposure to an antigen, producing memory cells |
| Herd immunity threshold, measles | around 95 per cent coverage |
| Booster doses | needed where immunity wanes or the pathogen changes |
| Live vaccines | generally avoided in significant immunosuppression |
What helps
- Take up every vaccine you are offered
- Keep a record; catch-up is available free at any age
- Ask a pharmacist, who can give several vaccines without an appointment
What to avoid
- Assuming childhood vaccination covers you for life
- Delaying travel vaccines, which often need weeks of lead time
- Relying on social media rather than the NHS schedule
Where to go next
- How Vaccines Work: The Questions People Actually Ask
- The Short Guide to How Vaccines Work
- The Childhood Schedule: What the Evidence Actually Says
- Flu Vaccination: Sorting the Evidence From the Noise
When to get help
Call 999 for swelling of the lips, tongue or throat, difficulty breathing or collapse after any vaccination — anaphylaxis is rare and immediate. Tell the vaccinator beforehand about allergies, immunosuppression, pregnancy, or a bleeding disorder.
Where this comes from
- UK Health Security Agency — immunisation schedules
- NHS — How vaccines work
How this page was put together
Every figure, recommendation and warning above is taken from the guidance named in Where this comes from. Nothing on this page is inferred, summarised or generalised beyond what those bodies publish: where they give a number, it is their number, and where they are silent, so are we. Pages are rebuilt whenever the underlying record changes. Sign-off by a named clinician, where it has happened, is shown at the top of the page along with the date.
Medical disclaimer
This article is general information, not medical advice. It cannot account for your own history, medication or circumstances. Always speak to a GP, pharmacist or another qualified health professional before making changes that affect your treatment, and never delay seeking medical advice because of something you have read here. In an emergency, call 999.