What is Haemophilus influenzae?
Haemophilus influenzae is a bacteria that can cause serious infection in humans, particularly in children, but also in individuals with weakened immune systems.
Are there different types of Haemophilus influenzae?
There are a number of strains of H. influenzae. Strains are classified as those with capsules (capsular types) and those without capsules (non-encapsulated types). Six capsular types (a-f) are recognised and more commonly cause invasive disease. The non-encapsulated strains cause mucosal infection (such as otitis media) but rarely lead to serious invasive disease.
What is Haemophilus influenzae type b?
H. influenzae type b (also known as "Hib") is just one of six H. influenzae types. Before a vaccine was available to prevent H. influenzae type b disease, Hib accounted for approximately 80-95% of all strains that caused invasive illness.
Invasive diseases caused by Hib are listed in the table below, along with their symptoms and complications.
Invasive disease caused by Hib
||Fever, refusing to feed, irritable/high-pitched cry in babies, pale or blotchy skin, being difficult to wake, stiff body with jerky movements or else floppy and listless, tense or bulging fontanelle.
Fifteen to thirty children in every hundred will develop long-term neurological problems, such as
- Hearing disorders
- Learning and language disability
- Delayed development
- Seizures (fits)
One child in every twenty who develop Hib meningitis may die.
||Swelling of the epiglottis causing noisy and painful breathing
||Severe blockage of the airway that can be fatal in up to 1 in 10 cases. |
||Fever, painful, red, hot and swollen joints
||Permanent damage to joints. Septicaemia |
|Fever, painful limbs
||Long-term bone infection|
||Sore, hot, painful area of skin
||Cough, breathing difficulties, chest pain
||Chest pain, breathing difficulties
How is Hib transmitted?
Hib lives in the nose and throat of humans and is transmitted from person to person through respiratory droplets, or contact with respiratory secretions. Humans are the only known reservoir. The bacteria may be carried around in the nose and throat for a short while or for several months without causing symptoms ("asymptomatic carrier"). In some individuals (particularly those most at risk) Hib will invade the body causing invasive disease (e.g. meningitis, septicaemia).
Who is most at risk of Hib infection?
Prior to the introduction of the Hib vaccine approximately 90% of all Hib disease occured in childen aged under 5 years. The highest incidence was in those aged under one year.
Young children, particularly, those aged under 4 years remain at the highest risk of Hib infection.
Other individuals at risk of Hib infection are individuals with an absent or malfunctioning spleen, and the immunocompromised, irrespective of how old they are.
When was the Hib Vaccine introduced?
The Hib vaccine was introduced into the national routine childhood immunisation schedule in 1992.
Who should be vaccinated?
All unvaccinated childre up to the age of 10 and those at increased risk of invasive Hib disease should be vaccinated.
Since 2008, Hib vaccine has been incorporated into the "six-in-one" vaccine (DTaP-IPV-Hib-Hep B) which is given at 2, 4 and 6 months of age.
Unvaccinated children, aged between 1 and 10 years, should recieve one dose of Hib vaccine.
Is a Hib booster necessary?
With time it became apparent that immunity to Hib from the three dose infant schedule waned and did not maintain protection in all children.
In response, the National Immunisation Advisory Committee (NIAC) recommended that a Hib booster vaccine at 13 months of age be included in the routine childhood immunisation programme.
All children reaching 13 months of age should now be given a Hib booster at the same time as their third dose of Men C vaccine. Booster vaccination is not normally required in children aged over 4 years.
What if a child has already received a dose of Hib or 6-in-1 after 12 months of age?
Any child who has received one dose of Hib or 6-in-1 after the age of 12 months has adequate protection and does not need any further doses of Hib vaccine.
What about persons at increased risk of invasive Hib disease?
Persons at increased risk of invasive Hib disease should be vaccinated. If aged less than one year the routine schedule should be followed. If aged over one year two doses of the Hib vaccine should be administered, two months apart.
What about children with a history of invasive Hib disease?
Children aged less than 2 years who develop invasive Hib disease should be given Hib vaccine after one month.
What is in the Hib vaccine?
The Hib vaccine is an inactivated conjugated polysaccharide vaccine. The Hib polysaccharide is conjegated to a protein, often tetanus toxoid. The Hib vaccine is not live and therefore cannot cause Hib disease.
Does the Hib vaccine contain thiomersal (mercury)?
No the Hib vaccine does not contain thiomersal.
How safe and effective is the Hib vaccine?
The Hib vaccine is highly effective. Since the introduction of the Hib vaccine in 1992 there has been a marked reduction in the number of invasive Hib infections in children. There has been a further reduction since the introduction of the Hib booster in 2005.
Hib vaccine has been proven to be one of the safest vaccines available. Over 20 million doses had been used worldwide and no serious adverse reactions had been reported. Since 1996 approximately 450,000 children have been vaccinated against Hib disease in Ireland and over that period just 39 cases acquired the disease despite being fully vaccinated.
Are there side effects from the Hib vaccine?
Local: These include local redness, warmth or swelling at the injection site. Mild local reactions occur in about 20% of children.
General:Systemic reactions are uncommon and include fever, irritability, headache, vomiting, diarrhoea and rashes. Seizures have rarely been reported.
Any adverse vaccine reactions (ADRs) should be reported to the Irish Medicines Board via the yellow report card (available on www.imb.ie).
Are there any reasons why the Hib vaccine should not be given?
Contraindications:Previous anaphylactic reaction to any component of the vaccine.
Precautions: Immunisation should be deferred in any child with acute febrile illness until the illness has resolved.
Hib vaccine may be given to immunocompromised patients, but adequate antibody levels may not be reached.
Vaccine should be adminstered with caution to people with bleeding disorders. Hiberix, the licenced monovalent Hib vaccine, can be administered by deep subcutaneous injection to such people.
- Immunisation Guidelines for Ireland. Immunisation Advisory Committee RCPI 2008. Available here
- HPSC Fact sheet Haemophilus Influenzae type B (Hib) www.hpsc.ie
- Heath PT, Booy R, Azzopardi HJ, Slack MP, Bowen-Morris J, Griffiths H, et al. Antibody Concentration and Clinical Protection After Hib Conjugate Vaccination in the United Kingdom. JAMA. 2000; 284:2334-2340
- Trotter CL, McVernon J, Andrews NJ, Burrage M, Ramsay ME. Antibody to Haemophilus influenzae type b after routine and catch-up vaccination. Lancet. 2003; 361:1523-4.
- Breukels MA, Spanjaard L, Sanders LA, Rijkers GT. Immunological characterization of conjugated Haemophilus influenzae type b vaccine failure in infants. Clin Infect Dis. 2001 Jun 15;32(12):1700-5. Epub 2001 May 16..
- McVernon J, Trotter CL, Slack MP, Ramsay ME. Trends in Haemophilus influenzae type b infections in adults in England and Wales: surveillance study. BMJ. 2004; 329: 655–658.