Haemophilus influenzae Type b Meningitis and Invasive Disease

Description

Haemophilus influenzae type b (Hib) causes meningitis and other severe bacterial infections (e.g., pneumonia, septic arthritis, epiglottitis, and sepsis), primarily among infants and children <5 years of age. Because Hib vaccine is used widely in the United States, the highest rate of reported invasive Hib disease is among infants too young to be fully vaccinated (<6 months of age); the incidence among infants and children 1–4 years of age is much lower than among infants <1 year of age. The disease is uncommon in anyone 5 years of age or more. Most cases occur in infants and children who are unvaccinated or incompletely vaccinated.

Occurrence

In the early 1980s (before licensure of conjugate Hib vaccines), approximately 20,000 cases of invasive Hib disease occurred annually in the United States, primarily among infants and children <5 years of age. As a result of the widespread use of conjugate Hib vaccines, the disease is now uncommon in the United States, with <200 cases reported annually.

Risk for Travelers

Invasive Hib disease occurs throughout the world. Few countries routinely use Hib vaccine, so invasive Hib disease remains common in many countries.

Prevention

Vaccine

Three conjugate Hib vaccines are licensed for use in infants: HbOC (HibTiTER, Wyeth-Lederle), PRP-OMP (PedvaxHIB, Merck & Co., Inc.), and PRP-T (ActHIB, Aventis Pasteur; OmniHIB, GlaxoSmithKline). A fourth Hib conjugate vaccine, PRP-D (ProHIBIT, Aventis Pasteur), is licensed only for infants and children 12–60 months of age and should not be used for the primary series. PRP-OMP vaccine is available combined with hepatitis B vaccine (Comvax). PRP-T (ActHIB) is also available combined with acellular pertussis vaccine (DTaP Tripedia). (The combined product is called TriHIBit.) However, TriHIBit is licensed for use only as the fourth dose of the Hib and DTaP series. It should not be given for the first, second, or third doses of the Hib series.

All infants, including those born prematurely, should receive a primary series of conjugate Hib vaccine (separate or as a combination vaccine), beginning at 2 months of age. The number of doses in the primary series depends on the type of vaccine used. A primary series of PRP-OMP (PedvaxHIB) vaccine is two doses; HbOC (HibTiTER) and PRP-T (ActHIB and OmniHIB) require a three-dose primary series (see Table 3–3). A booster should be given at 12–15 months of age, regardless of which vaccine is used for the primary series.

The optimal interval between doses is 2 months, with a minimum interval of 1 month. At least 2 months should separate the booster dose from the previous (second or third) dose. Hib vaccines may be given simultaneously with all other vaccines.

Limited data suggest that if Hib conjugate vaccines are given to infants <6 weeks of age, they may induce immunologic tolerance to additional doses of Hib vaccine. Therefore, Hib vaccines, including combination vaccines that contain Hib conjugate, should not be given to a child <6 weeks of age.

All three conjugate Hib vaccines licensed for use in infants are interchangeable. A series that includes vaccines of more than one type will induce a protective antibody level. If it is necessary to change the type of vaccine, three doses of any combination constitute the primary series. Any licensed conjugate vaccine may be used for the booster dose, regardless of what type was received in the primary series.

Unvaccinated infants and children 7 months of age or more might not require a full series of three or four doses. The number of doses an infant or a child needs to complete the series depends primarily on the infant's or child's age at the time and, to a lesser degree, on the number of prior doses of Hib vaccine received. Previously unvaccinated infants and children 15–60 months of age should receive a single dose of any conjugate Hib vaccine. In general, children >60 months of age do not need Hib vaccination. Refer to the American Academy of Pediatrics Red Book for additional information on late or lapsed Hib vaccination schedules.

Adverse Reactions

Adverse events following vaccination with Hib conjugates are uncommon. Swelling, redness, or pain, or a combination of these, have been reported in 5%–30% of recipients and usually resolve within 12–24 hours. Systemic reactions such as fever and irritability are infrequent.

Precautions and Contraindications

Vaccination with Hib conjugate vaccine is contraindicated in anyone known to have experienced anaphylaxis following a prior dose of that vaccine. Vaccination should be delayed in infants and children with moderate or severe acute illnesses. Minor illnesses (for example, mild upper respiratory infection) are not contraindications to vaccination. Contraindications and precautions for the use of TriHIBit and Comvax are the same as those for their individual component vaccines (i.e., DTaP, Hib, and hepatitis B).

Treatment

Specific antibiotic treatment is necessary for invasive Hib disease. In certain circumstances, antibiotic prophylaxis is indicated for household contacts. Refer to the American Academy of Pediatrics Red Book for additional information.

— Margaret Cortese