Haemophilus influenzae type b (Hib) is usually a non-pathogenic commensal bacterium. Vaccination has meant carriage rates have fallen below detection levels in young children and infection is rare.12,31

If it becomes pathogenic, it can cause severe, life-threatening infections, including meningitis (60 per cent of cases), septicaemia, pneumonia, pericarditis, epiglottitis with breathing difficulties (15 per cent of cases), septic arthritis, cellulitis, and osteomyelitis.

Even with antibiotics treatment in hospital, potentially one in 20 children developing Hib meningitis will die, while those surviving may be left with hearing loss, seizures or learning disabilities.

Mumps, a viral infection characterised by swellings of the parotid glands behind the ears, does not usually cause long-term health damage, and serious complications are rare. However, it can cause viral meningitis in one in seven cases, and pancreatitis and/or temporary hearing loss in one in 20 cases. Mumps contracted post-puberty can cause testicle pain and swelling (orchitis) in one in four males, and swollen ovaries (oophoritis) in one in 20 females.32

Rarer complications include encephalitis from the viral meningitis (one in 7,000 cases), and permanent hearing loss (one in 200,000 cases). The NHS advises that pregnant women avoid contact with people with an active mumps infection as a precaution, but says there is currently little evidence to support the belief that mumps increases the risk of miscarriage.

Rubella, is another viral infection characterised bya body rash, and sometimes with swollen glands in the neck or cold/flu-like symptoms. It can increase the risk of miscarriage or of serious conditions developing in the unborn child, including problems with their sight, hearing, heart or brain.4

Rotavirus, with its severe watery diarrhoea, can lead to extreme dehydration. Around one in five children will need to see a doctor, and one in 10 will require hospital treatment. The vaccine does not protect every child, but is estimated to prevent more than 70 per cent of cases, and may reduce disease severity if it occurs.33,34

Pertussis is a distressing bacterial disease of the lungs and airways which can cause severe coughing bouts for several months. It can affect anyone, but is of particular concern in infants who are more susceptible to complications and are likely to need hospital care.35

The cough is usually productive with thick mucus, but the strain from coughing can cause bleeding under the skin or eyes. The whooping sound when gasping for breath is not always present, but breathlessness may cause cyanosis with the skin appearing to turn blue. Dehydration and weight loss are common. While older children and adults may be less severely affected, they can experience nosebleeds, bruised ribs or hernia. More serious complications include seizures, brain damage, kidney damage or pneumonia, and it can be fatal.

Diphtheria is highly contagious and potentially fatal. It is rare in the UK, but is endemic in some parts of the world, so travel may present a particular risk. Bacteria secrete a toxin which produces membrane-like coatings in the throat and upper respiratory tract and may damage the myocardium. While its main effect is to impair breathing and swallowing, it can also cause skin blisters and ulceration.36,37

Polio is highly infectious, usually being transmitted via the faecal-oral route, and can enter the nervous system from the gut causing total paralysis within a few hours. Around 1 in 200 infections result in irreversible paralysis (usually the legs), but up to 10 per cent of those paralysed will die due to breathing muscles becoming immobilised.15