|Target disease||Haemophilus influenzae type b|
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Haemophilus influenzae type B vaccine is a vaccine used to prevent Haemophilus influenzae type b (Hib) infection. In countries that include it as a routine vaccine, rates of severe Hib infections have decreased more than 90%. It has therefore resulted in a decrease in the rate of meningitis, pneumonia, and epiglottitis.
It is recommended by both the World Health Organization and Centers for Disease Control and Prevention. Two or three doses should be given before six months of age. The first dose is recommended around six weeks of age with four weeks between doses. If only two doses are used, another dose later in life is recommended. It is given by injection into a muscle.
Severe side effects are uncommon. About 20 to 25% of people develop pain at the site of injection while about 2% develop a fever. There is no clear association with severe allergic reactions. The Hib vaccine is available by itself, in combination with the diptheria/tetanus/pertussis vaccine, and in combination with the hepatitis B vaccine, among others. All Hib vaccines that are currently used are conjugate vaccine.
An initial Hib vaccine was developed in 1977 which was replaced by a more effective formulation in the 1990s. As of 2013, 184 countries include it in their routine vaccinations. It is on the World Health Organization's List of Essential Medicines, the most important medications needed in a basic health system. The wholesale cost of a pentavalent vaccine which includes Hib was 15.40 USD per dose as of 2014. In the United States it costs about 25 to 50 USD per dose.
Hib conjugate vaccines have been shown to be universally effective against all manifestations of Hib disease, with a clinical efficacy among fully vaccinated children estimated to be between 95–100%. The vaccine has also been shown to be immunogenic in patients at high risk of invasive disease. Hib vaccine is not effective against non-type B Haemophilus influenzae. However, non-type B disease is rare in comparison to pre-vaccine Haemophilus influenzae type B disease.
Prior to introduction of the conjugate vaccine, Hib was a leading cause of childhood meningitis, pneumonia, and epiglottitis in the United States, causing an estimated 20,000 cases a year in the early 1980s, mostly in children under 5 years old. Since routine vaccination began, the incidence of Hib disease has declined by greater than 99%, effectively eliminating Hib as a public health problem. Similar reductions in disease occurred after introduction of the vaccine in Western Europe and developing countries.
Although Hib vaccine is given to children, Hib infections have also decreased in adults. This decrease occurred because of herd immunity; children infected with Hib carry the bacteria in their nasal passages while clearing the infection. These Hib-carrying children would regularly infect adults. The practice of vaccinating children eliminated the source of the bacteria, reducing the rate of Hib in adults.
The CDC and WHO currently recommend that all infants be vaccinated using a polysaccharide-protein conjugate Hib vaccine, starting after the age of 6 weeks. The vaccination is also indicated in asplenic patients.
Clinical trials and ongoing surveillance have shown Hib vaccine to be safe. In general, adverse reactions to the vaccine are mild. The most common reactions are mild fever, loss of appetite, transient redness, swelling, or pain at the site of injection, occurring in 5–30% of vaccine recipients. More severe reactions are extremely rare.
Introduction of Hib vaccine in developing countries lagged behind that in developed countries for several reasons. The expense of the vaccine was large in comparison to the standard EPI vaccines. Poor disease surveillance systems and inadequate hospital laboratories failed to detect the disease, leading many experts to believe that Hib did not exist in their countries. And health systems in many countries were struggling with the current vaccines they were trying to deliver.
GAVI and the Hib Initiative
In order to remedy these issues, the GAVI Alliance took active interest in the vaccine. GAVI offers substantial subsidization of Hib vaccine for countries interested in using the vaccine, as well as financial support for vaccine systems and safe injections. In addition, GAVI created the Hib Initiative to catalyze uptake of the vaccine. The Hib Initiative uses a combination of collecting and disseminating existing data, research, and advocacy to assist countries in the making a decision about using the Hib vaccine. Currently[update], 61 out of 72 low-income countries are planning on introducing the vaccine by the end of 2009.
The first Hib vaccine licensed was a pure polysaccharide vaccine, first marketed in the US in 1985. Similar to other polysaccharide vaccines, immune response to the vaccine was highly age-dependent. Children under 18 months of age did not produce a positive response for this vaccine. As a result, the age group with the highest incidence of Hib disease was unprotected, limiting the usefulness of the vaccine. The vaccine was withdrawn from the market in 1988.
The shortcomings of the polysaccharide vaccine led to the production of the Hib polysaccharide-protein conjugate vaccine. Attaching Hib polysaccharide to a protein carrier greatly increased the ability of the immune system of young children to recognize the polysaccharide and develop immunity. There are currently three types of conjugate vaccine, utilizing different carrier proteins for the conjugation process, all of which are highly effective and safe: inactivated tetanospasmin (also called tetanus toxoid), mutant diphtheria protein, and meningococcal group B outer membrane protein.
Multiple combinations of Hib and other vaccines have been licensed in the United States, reducing the number of shots necessary to vaccinate a child. Hib vaccine combined with diphtheria-tetanus-pertussis–polio vaccines and Hepatitis B vaccines are available in the US. The World Health Organization (WHO) has certified several Hib vaccine combinations, including a pentavalent diphtheria-pertussis-tetanus-hepatitis B-Hib, for use in developing countries. There is not yet sufficient evidence on how effective this combined pentavalent vaccine is in relation to the individual vaccines.
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- "Hib Initiative". Retrieved 2008-10-03.
61 of 72 GAVI countries have introduced or will introduce Hib vaccine into their routine immunization program [sic] by 2009
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