Haemophilus influenzae type b (Hib)
20 February 2012
- Haemophilus influenzae type b, or Hib, is a bacterium estimated to be responsible for some eight million serious illnesses and an estimated 371 000 deaths per year, chiefly through meningitis and pneumonia.
- Almost all victims are children under the age of five, with those between four and 18 months of age especially vulnerable.
- In developing countries, where the vast majority of Hib deaths occur, pneumonia accounts for a larger number of deaths than meningitis.
- However, Hib meningitis is also a serious problem in such countries, with mortality rates several times higher than seen in developed countries. The disesase leaves 15%-35% of survivors with permanent disabilities such as mental retardation or deafness.
- Hib vaccines are safe and highly effective, and WHO recommends that Hib vaccine be included in all routine infant immunization programmes.
- Contrary to what the name Haemophilus influenzae suggests, the bacterium does not cause influenza.
The Hib challenge
- Hib is preventable. Highly effective vaccines have been available since the early 1990s, yet hundreds of thousands of children die year after year from Hib disease.
- The two major obstacles to prevention are a shortage of information and a shortage of money.
- The information shortage is largely due to the difficulty of diagnosing Hib disease. It claims most of its victims without ever being recognized.
- The money factor is that Hib vaccine is more expensive than classic childhood vaccines, generally costing more than the total cost of vaccines against measles, polio, tuberculosis, diphtheria, tetanus, and pertussis.
- Those two factors put many developing countries in a difficult situation. However, in recent years many countries have completed studies to measure the burden of Hib disease and have decided to add Hib vaccine to their infant immunization programmes.
- The GAVI alliance supports Hib vaccine, as part of a combination vaccine against diphtheria, tetanus, pertussis and hepatitis B, in many low and lower middle income countries.
Hib burden and vaccination in industrialized countries
- Industrialized countries, with sophisticated health-surveillance systems, became aware of the threat posed by Hib as long as 50 years ago.
- Before immunization programmes began in the early 1990s, Hib was demonstrated to be the leading cause of childhood bacterial meningitis in nearly all countries in which appropriate studies were performed, including Australia, Canada, Finland, the Netherlands, Sweden and the United States of America.
- The rate of Hib-caused pneumonia in developed countries was not clear, although it was considered to occur less often than meningitis – the opposite of the situation in the developing world.
- Systematic vaccination has now virtually eliminated Hib disease in most industrialized nations.
A hidden disease
- Hib is commonly found in the noses and throats of healthy individuals living in regions where vaccination is not carried out.
- Almost all unvaccinated children are exposed to Hib by age five. The bacterium is spread by exhaled droplets.
- Occasionally, Hib can invade the bloodstream and cause infection and disease in other parts of the body, including the meninges (membranes enveloping the brain and spinal cord) leading to meningitis, and the lungs, causing pneumonia.
- Unlike measles, polio or diphtheria, Hib does not cause a specific illness with which it, alone, can be identified.
- The most deadly forms of Hib infection include pneumonia and meningitis, but those diseases can have other causes, and can look the same whether caused by Hib or some other agent.
- More rarely, Hib is responsible for other life-threatening complications in young children, such as septic arthritis, an inflammation of the joints, and septicaemia, or blood poisoning, both of which also can have other causes.
- Hib may also lead to epiglottitis (a life-threatening inflammation of the flexible cartilage that covers the gap in the vocal cords during swallowing).
- Doctors treating cases of childhood pneumonia or meningitis tend to respond quickly with antibiotics in an effort to save lives. But to confirm a case of Hib, samples must be taken from an ill person — a blood specimen in the case of pneumonia, and a spinal-fluid specimen by lumbar puncture in the case of meningitis. The bacteria must then be isolated from those specimens in a laboratory.
- That is a challenge even for sophisticated laboratories. In developing countries, such tests may not be made at all, or laboratories may fail to carry them out correctly, or Hib's presence may be masked because antibiotics were given before the samples were taken.
- The hidden nature of Hib means its impact is often underestimated. Studies have shown a lack of awareness of Hib among medical professionals in some developing countries, or have shown that they associate Hib only with meningitis – when in fact Hib pneumonia occurs five times as frequently in such countries.
Assessing the incidence of Hib
- A "Rapid Assessment Tool" has been developed by WHO and the United States Centers for Disease Control and Prevention (CDC) to allow countries to make estimates of the extent of Hib disease by studying past hospital records, childhood mortality rates, or pneumonia mortality rates.
- The Hib Initiative, supported through the GAVI Alliance, helped many countries estimate the burden of Hib disease through sentinel surveillance and special studies.
- WHO has completed a systematic review of data and provided estimates to each Member State on the incidence of severe illness and death caused by Hib.
- Treatment of Hib is through a course of antibiotics, but this is not always accessible to poor populations in developing countries.
- Resistance of Hib to several of the more inexpensive but effective antibiotics is a growing cause of concern and provides additional impetus for expanding vaccine coverage.
- Hib conjugate vaccines, given by intramuscular injection, are highly effective and have almost no side-effects.
- Three doses are usually administered in infancy, starting at around age six weeks. In some countries, a booster dose is also offered between 12 and 18 months of age, although this might not be necessary in countries where Hib disease incidence is high in infancy, such as many developing countries.
- Increasingly, Hib vaccines are administered as part of combination vaccines that can also include protection against diphtheria, tetanus, pertussis, and hepatitis B.
- As of October 2011, 171 of the 193 Member States (89%) had adopted Hib vaccine in their routine immunization programmes.
- WHO is an active participant in the GAVI Alliance that assists poorer countries in introducing the vaccine in a sustainable fashion.
- WHO has developed management guidelines for the introduction of Hib vaccine into immunization programmes.
- The Global Immunization Vision and Strategy (GIVS), developed by WHO, UNICEF, and partners, has among its aims "strengthening the current immunization system so that it can maximally deliver currently available vaccines as well as under-utilized vaccines," including Hib.