This glossary covers the vaccines and diseases that appear across the childhood immunisation schedules on this site. Not every vaccine is used in every country - your country's page shows which apply to your child and when. For anything specific to your child, talk to your GP, health visitor or paediatrician.
6-in-1 / hexavalent (DTaP-IPV-Hib-HepB)
One injection that protects against diphtheria, tetanus, whooping cough (pertussis), polio, Haemophilus influenzae type b (Hib) and hepatitis B. It is the backbone of the infant schedule in the UK, Ireland, Australia, Germany and many other countries.
Diphtheria
A bacterial infection that produces a toxin, causing a thick grey coating at the back of the throat that can block breathing, and damage to the heart and nerves.
Tetanus
Caused by bacteria in soil and dust entering a wound. The toxin causes severe, prolonged muscle spasms, starting with the jaw, and can be fatal.
Whooping cough (pertussis)
A bacterial infection causing violent coughing fits that make it hard to breathe, often ending in a 'whoop'. In young babies it can cause pauses in breathing, pneumonia and death, sometimes without an obvious cough.
Polio (poliomyelitis)
A virus that usually causes a mild illness but in a small number of cases attacks the nervous system, causing permanent paralysis - sometimes of the muscles used to breathe.
Haemophilus influenzae type b (Hib)
A bacterium (not related to influenza) that was the most common cause of bacterial meningitis in young children before vaccination, and also causes a dangerous throat swelling called epiglottitis.
Hepatitis B
A virus that infects the liver. Caught in infancy it usually becomes a lifelong (chronic) infection that can lead to cirrhosis and liver cancer decades later.
Pneumococcal (PCV)
Protects against Streptococcus pneumoniae, a common bacterium that causes ear infections, sinusitis and pneumonia, and less often meningitis and bloodstream infection.
Rotavirus
The most common cause of severe diarrhoea and vomiting in babies and toddlers, leading to dehydration that often needs hospital treatment.
MMR (measles, mumps, rubella)
A single injection against three viruses. Measles: fever, rash, and in some cases pneumonia, deafness or brain swelling. Mumps: swollen glands, sometimes meningitis or hearing loss. Rubella: mild in children but causes serious birth defects in pregnancy.
Meningococcal B (MenB)
Protects against group B meningococcal bacteria, the most common cause of meningococcal meningitis and sepsis (blood poisoning) in young children in Europe.
Meningococcal ACWY (MenACWY)
Protects against four groups (A, C, W and Y) of meningococcal bacteria.
Meningococcal C (MenC)
Protects specifically against group C meningococcal disease.
Varicella (chickenpox)
Prevents chickenpox: an itchy blistering rash with fever. Usually mild, but can cause serious skin infection, pneumonia, or inflammation of the brain, and is dangerous for newborns and people with weak immune systems.
HPV (human papillomavirus)
Protects against the types of HPV that cause almost all cervical cancer, most anal cancer, and a large share of mouth, throat, penile and vulval cancers, plus genital warts.
Hepatitis A
A liver infection spread through contaminated food and water, causing weeks of jaundice, nausea and fatigue. Rarely fatal but very unpleasant and disruptive.
BCG (tuberculosis)
Given as a single injection, usually into the upper arm, leaving a small scar. It does not prevent all TB but strongly protects babies and young children against the most severe forms - TB meningitis and disseminated (miliary) TB.
Influenza (flu)
Protects against seasonal flu, which in young children can cause high fever, pneumonia, and occasionally inflammation of the brain, and leads to many hospital admissions each winter.
Japanese encephalitis (JE)
A mosquito-borne virus that infects the brain. Most infections cause no symptoms, but severe cases have a high rate of death or lasting disability.
Yellow fever
A mosquito-borne virus causing fever and, in severe cases, jaundice, bleeding and organ failure. One dose gives lifelong protection.
RSV protection (nirsevimab / maternal vaccine)
Not a traditional childhood vaccine: either a single long-acting antibody injection (nirsevimab) given to babies, or a vaccine given to the mother in pregnancy, to protect against respiratory syncytial virus.
How to think about the schedule as a whole
Read down a schedule and a pattern emerges. The first year front-loads protection against the infections most dangerous to babies - whooping cough, Hib, pneumococcus, meningococcus, rotavirus - with several closely spaced doses because one dose is not enough to build full immunity. The second year adds the live vaccines that work best slightly later (measles-mumps-rubella, chickenpox) and a round of boosters. The pre-school visit tops up the diphtheria-tetanus-whooping cough-polio group before children mix in larger numbers. The teenage visits refresh tetanus and diphtheria for adult life, broaden meningococcal cover for the higher-risk late teens, and add HPV before any exposure.
Every dose and every interval in that pattern is chosen for the specific biology of the vaccine involved, which is why the schedules look intricate rather than uniform.