Contents:
Introduction
Disease
Vaccines
Issues
Additional Links
While a successful vaccine exists for the elimination of Haemophilus influenzae type B (Hib), only 34 countries around the world have fully integrated it into vaccination programs for children. In most of the developing world, Hib infection is still one of the greatest killers of children under the age of 5. Each year an estimated 3 million plus cases of Hib disease and some 700,000 Hib-related deaths occurr worldwide. This gram negative bacteria colonies the nasopharynx area and can cause illnesses such as pneumonia and meningitis. Children who survive Hib meningitis often face permanent neurological disability, including brain damage, hearing loss, and mental retardation. The spread of the Hib vaccine around the world has been slow because of numerous obstacles.
map:WHO (2)
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Disease
Pathogen
Hib is caused by the bacterium Haemophilus
influenzae type B, a gram negative bacteria, usually aerobic, which
colonizes in the nasopharynx area of its host, specifically the nose, throat,
and upper respiratory tracts. H. Influenzae can be isolated
in the encapsulated or the unencapsulated forms; six capsular types have
been identified and named a through f. All isolates from cerebrospinal
fluid and blood are mostly of type b. The capsules of Hib are composed
of a polysaccharide which is responsible for virulence and immunity. (3)
Transmission/Infection
Hib can be transmitted in droplet form from
person to person through sneezing, coughing, or speaking closely.
Asymtomatic carriers are a major source of infection; thus the bacteria
can pass through several individuals before it reaches a susceptible person.
In some individuals, the pathogen can invade the blood stream and cause
an invasive infection; exactly what accounts for this mode of invasion
is not known. Upon entry to the blood stream and spread to distinct
sites, Hib can cause pneumonia, more often in developing countries, or
meningitis, more often in developed countries. Other manifestations
may include inflammation of the throat, tissues around the eyes, joints,
bones or membranes surrounding the heart or lungs.(4)
Immunity
Several factors increase the risk of disease
in children under the age of 5. These include failure to breast feed,
the younger the age of children, the presence of underlying illness, or
household crowding. Risk of disease is highest among children between
6 months and 2 years and low in first 6 months. Passive protection
of some infants is provided by transplacentally acquired maternal IgG antibodies
and breast-feeding during the first 6 months of age. Hib is uncommon
beyond 5 years of age, presumably because the acquisition of humoral immunity
to Hib with increasing age.(5)
Antibodies to capsular polysaccharide proteins are protective. The exact levels of antibody required for protection against invasive disease is not clearly established.
In Haemophilus influenzae, a gram negative
pleomorphic rod appears pink in gram stain. (6)
http://www.vh.org/Providers/Textbooks/ElectricAirway/PathImages/HInfluenzaGramStain.html
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Treatment/Vaccines 
In developed countries, often Hib infection can be treated with existing antibiotics; however, in many parts of the world new strains are emerging that demonstrate increasing resistance to there drugs.
A pure polysaccharide vaccine was developed in the US in 1985; however, this vaccine was ineffective in children under the age of 2 and had varying efficacy in older children. The response to the vaccine was of a T independent antigen, with mostly IgM antibodies. This vaccine showed poor class switching to IgG and no boost in antibody titer was observed with booster shots. This vaccine is no longer available in the US.
Several Hib conjugate vaccines have been licensed since then. These prove to be much more effective because the conjugation of the polysaccharide to a protein carrier changes the response from a primarily T independent one to a T dependent one, thus raising immunogenicity, especially in young children. Hib conjugated vaccines have demonstrated excellent protective efficacy in early infancy, and are now one of the safest of all vaccines. These conjugated vaccines are now routinely used in childhood vaccination in 34 countries or territories around the world. (see map above). Hib has virtually disappeared from these countries. (6)
The vaccines are developed by having Hib polysaccharide conjugated to a protein carrier such as diphtheria toxoid (PRP-D), a diphtheria toxoid like protein (PRP-HbOC), tetanus toxoid (PRP-T), or meningococcal outer membrane protein (PRP-OMP). All types of conjugated vaccines are highly immunogenic conferring more than 95% protection in infants receiving the complete series. Six vaccines are currently on the market. All conjugate Hib vaccines are given intramuscularly, in the anterolateral thigh area or the outer aspect of the upper arm; they are administered at 2,4, and 6 months of age with a booster at 12 to 18 months of age. Hib vaccines should not be given to children under the age of 6 weeks because of the risk that the first dose may induce immunologic tolerance to subsequent doses if given prior to 6 weeks of age.(7)
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Issues
*Increased resistance to antibiotics
*The Economics of
Vaccine Development and Program Implementation
High cost of these vaccines as compared with
other traditional childhood vaccines used in EPI
Bacterial
Meningitis
http://www.childrensvaccine.com/html/hib_qf.htm