In short: Live vaccines contain a weakened form of a germ that can still multiply a little in the body, producing strong, long-lasting immunity, often after one or two doses. Inactivated and other non-live vaccines contain killed germs, parts of germs or instructions to make a protein, so they cannot cause infection but may need several doses or boosters. Live vaccines are usually avoided in pregnancy and in people with weakened immune systems, which is why a clinician checks your health before vaccination.

This guide, written by a Ready Health prescribing pharmacist, explains the main types of vaccine used in the UK and why the difference matters.

How do vaccines work?

All vaccines work by showing your immune system something that looks like a particular germ, without you having to suffer the illness. Your body makes antibodies and memory cells, so if you meet the real infection later you can respond quickly. The main difference between vaccine types is what is used to trigger that response.

What is a live vaccine?

A live attenuated vaccine uses a weakened version of a virus or bacterium. It can replicate a small amount without causing disease in healthy people, which closely mimics natural infection and tends to give strong, long-lasting protection.

Examples used in the UK include:

MMR (measles, mumps and rubella) and MMRV, which also includes chickenpox
Nasal flu vaccine for children
Rotavirus vaccine (oral, for babies)
BCG (tuberculosis)
Yellow fever vaccine
Some oral travel vaccines, such as the live oral cholera vaccine

What is an inactivated or non-live vaccine?

Non-live vaccines cannot replicate or cause infection. There are several kinds:

Inactivated (killed) vaccines: for example, polio (IPV), hepatitis A, rabies, Japanese encephalitis and tick-borne encephalitis vaccines.
Subunit, recombinant and conjugate vaccines: use selected parts of the germ, such as proteins or sugars. Examples include hepatitis B, HPV, the shingles vaccine used on the NHS, MenB, MenACWY, pneumococcal and the typhoid injection.
Toxoid vaccines: use an inactivated toxin, as in tetanus and diphtheria vaccines.
mRNA and viral vector vaccines: give the body instructions to make a harmless protein, as with some COVID-19 vaccines. They do not alter your DNA.

Live vs inactivated vaccines: what is the difference?

	Live vaccines	Inactivated and other non-live vaccines
What they contain	Weakened living germ	Killed germ, part of a germ, inactivated toxin or genetic instructions
Can they cause infection?	Not in healthy people, but can cause a mild illness-like reaction	No
Number of doses	Often one or two	Often several, sometimes with boosters
Pregnancy	Usually avoided	Many are safe and some are recommended (for example flu, whooping cough and RSV)
Weakened immune system	Usually not given	Can usually be given, although the response may be weaker
Timing with other live vaccines	Some need to be given on the same day or spaced apart	Can generally be given at any interval

Who should not have live vaccines?

People with significantly weakened immune systems, for example due to some cancers, treatments such as chemotherapy, high-dose steroids or certain biological medicines, or untreated HIV with low CD4 counts.
Pregnant women (pregnancy is usually also advised against for a short period after some live vaccines).
Anyone who has had a severe allergic reaction to a previous dose or an ingredient.

There are exceptions and specialist advice is sometimes needed, so always tell the person vaccinating you about your medicines, conditions and whether you are or may be pregnant.

Frequently asked questions

Are live vaccines safe?

Yes, for the people they are recommended for. They have been used for decades and are monitored by the MHRA. The main precaution is avoiding them in people whose immune systems cannot control the weakened germ.

Can I have a live travel vaccine and the MMR at the same time?

Some live vaccines can be given on the same day, while others are better separated by about 4 weeks. Your clinician will plan the timing using UK Green Book guidance.

Is the flu jab live?

The injected flu vaccines given to adults are inactivated. The nasal spray flu vaccine offered to children is live.

Why do some vaccines need boosters?

Non-live vaccines can produce a less durable response, so additional doses help maintain protection. Booster schedules vary by vaccine and by your ongoing risk.

Key takeaways

Live vaccines use weakened germs and usually give long-lasting immunity with few doses.
Non-live vaccines cannot cause infection but may need more doses or boosters.
Live vaccines are generally avoided in pregnancy and in people with weakened immune systems.
Timing between live vaccines may need planning, especially before travel.

Sources and further reading

Last reviewed: October 2026 by Shamir Patel, Independent Prescribing Pharmacist, Ready Health. This article is general information and does not replace advice from your own clinician.

Need advice on which vaccines are suitable before you travel? Book a travel clinic consultation at Ready Health in Standish, convenient for Wigan, Chorley and Bolton.

Live vs Inactivated Vaccines: How They Work and Differ