HIB Vaccination

Haemophilus influenzae type b (Hib) is an important cause of childhood meningitis and pneumonia. It is estimated to cause at least 3 million cases of invasive disease and up to 700 000 deaths worldwide, annually. Expression of the polysaccharide capsule increases bacterial virulence and is associated with severe disease. Vaccination confers protection by induction of anticapsular antibodies and immunological memory. Conjugate Hib vaccines were introduced during the 1990s and are considered safe and highly efficacious.¹

The clinical efficacy of the conjugate Hib vaccines is estimated as 94-100%.² However, there was a reduction in efficacy of Hib-TT vaccines in the UK between 1999 and 2003 which remains unexplained and was unrelated to the quality of the vaccine.³ The vaccine used in the current UK primary schedule induces protective antibody levels in 90-99% of children.⁴ The vaccination also reduces nasopharyngeal carriage in asymptomatic carriers and therefore confers herd immunity to unvaccinated children.⁵ The uptake of Hib vaccine peaked in the UK during the late 1990s. From 2002 to 2004, the Hib vaccine 2-year coverage rates in England remained stable at 93%.⁶

Conjugate Hib vaccination was introduced into the UK routine childhood immunisation schedule in 1992. In 1996, the single Hib vaccine was replaced by a DTP/Hib combination⁴ but due to a shortage of product, a preparation containing acellular pertussis (DTaP/Hib) was used during 2000 and 2001. The original DTP/Hib combination was subsequently reintroduced⁷ but was replaced by the current DTaP/IPV/Hib vaccine in 2004.⁴

The introduction of immunisation in the UK caused an immediate decline in the incidence of Hib. Only 37 Hib isolates were identified in England and Wales in 1998, compared with 892 cases in 1991. However the incidence of disease then increased to a maximum of 269 Hib cases in 2002.⁸ It has since been confirmed that the temporary DTaP/Hib vaccine was less immunogenic and is believed to have contributed to recent vaccination failures. A Hib booster campaign was therefore launched in 2003 to reinforce immunity in young children⁷ and the incidence of infection has again decreased.⁸

Hib vaccines are composed of capsular polysaccharide from cultured Haemophilus influenzae type b bacteria, conjugated to protein to strengthen immunogenicity.
The Hib vaccine is available as a single or combined product:

• Monovalent Hib vaccine
• Diphtheria/ tetanus/ acellular pertussis/inactivated polio/ Haemophilus influenzae type b (DTaP/IPV/Hib) vaccine.

Although the current DTaP/IPV/Hib vaccine contains an acellular pertussis component, the preparation does induce an effective immunological response to Hib antigens.

Hib vaccines are injected intramuscularly. Upper arm or anterolateral thigh sites are recommended to minimise the risk of local reactions. Other vaccinations such as MMR, MenC or hepatitis B can be given at the same time but should be injected at an alternative site and preferably in a different limb.

All infants should receive the primary Hib immunisation course. The DTaP/IPV/Hib vaccine is given at 2, 3 and 4 months of age, whilst levels of maternal antibodies wane.⁹ If primary immunisation has been delayed, children up to 10 years of age can be given 3 doses of combination vaccine at monthly intervals. Although only one dose of Hib vaccine is necessary to achieve immunity in children aged over one year, the extra doses are required to provide immunity to diphtheria, tetanus, whooping cough and polio. Children are currently being given boosters with there preschool jabs.

The monovalent Hib vaccination is given to individuals who have completed the primary immunisation course for diphtheria, tetanus, whooping cough and polio but not Hib. This should only apply to those vaccinated outside the UK. The same dosing regimens are applicable.

Immigrants

The cost of the Hib vaccine has prevented its use in routine childhood immunisation schedules in many poorer countries.⁵ Children from developing countries may therefore have not received the vaccination. If the history is unclear, children are considered unimmunised and should complete the full UK schedule.

Splenic dysfunction

Individuals with splenic dysfunction are at increased risk of invasive Hib infection. Children under 10 years of age should complete the primary immunisation course. Unimmunised children aged over 10 years and adults should receive a single dose of monovalent Hib vaccine. It is recommended that individuals immunised in infancy who subsequently develop splenic dysfunction, should receive a single monovalent Hib booster (after one year of age). Patients undergoing splenectomy should ideally be offered the vaccine 2 weeks before surgery, or as soon as possible postoperatively.

Index cases

Unimmunised patients with diagnosed Hib infections should be immunised as recurrence of disease can occur. Patients who have been immunised but later acquire Hib infection may benefit from a booster dose of vaccine, depending on convalescent antibody levels.

Contacts

Children who are household contacts of an index case should be fully immunised as per previous recommendations.

The vaccination should not be administered to individuals with:

• Confirmed anaphylactic reaction to Hib-containing vaccine
• Confirmed anaphylactic reaction to neomycin, streptomycin or polymyxin B, as they may be present in small amounts
• Acute illness with systemic upset and fever
• Evolving or undiagnosed, deteriorating neurological abnormalities.

The following situations do not prohibit vaccination:

• History of a stable neurological condition, seizures or febrile convulsions (without neurological deterioration)
• There is no evidence of increased risks of adverse reactions from vaccinations in preterm babies: premature infants should receive vaccinations at appropriate chronological age, according to the schedule
• Fever, persistent screaming, severe local reactions or hypotonic-hyporesponsive episodes following previous Hib-containing vaccinations
• Immunosuppression including HIV infection (but individuals may not achieve an adequate immunological response and may benefit from reimmunisation)
• Pregnancy or breast-feeding.

The recent increase in atopy may be due to vaccines in childhood. This includes the following vaccines: diphtheria, pertussis, poliomyelitis, tetanus and Hib. However, these fears are at present unfounded and the presence of atopic illnesses does not differ between those who receive full vaccination, partial vaccination schedule nor in those who have never been vaccinated.¹⁰