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Haemophilus influenzae type b (Hib) is a bacterium that can cause a number of serious illnesses, particularly in young children.
Hib infections used to be a serious health problem in the UK, but the routine immunisation against Hib, given to infants since 1992, means these infections are now rare.
Of the small number of cases that do occur nowadays, most affect adults with long-term (chronic) underlying medical conditions, rather than young children.
Hib bacteria can cause several serious infections, including:
Many children who develop Hib infections become very ill and need treatment with antibiotics in hospital.
Meningitis is the most severe illness caused by Hib. Even with treatment, 1 in every 20 children with Hib meningitis will die.
Hib bacteria can live in the nose and throat of healthy people, and usually don't cause any symptoms.
The bacteria can be spread by healthy people who carry the bacteria, as well as those who are ill with a Hib infection.
Inhaling the infected droplets or transferring them into your mouth from a contaminated surface can allow the bacteria to spread further into your body, causing one of the infections mentioned above.
Vaccinating children against Hib has been very effective in cutting rates of Hib infections.
From more than 800 confirmed cases a year in England in the early 1990s, the number of Hib infections has now fallen to fewer than 20 cases a year.
The Hib vaccine is routinely offered to babies as part of the NHS childhood vaccination programme.
Babies have three separate doses of Hib vaccine – at 8, 12 and 16 weeks of age – as part of the combined 6-in-1 vaccine.
A booster dose is also offered when a child is one year old as part of the combined Hib/MenC booster to provide longer-term protection.