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ABBREVIATIONS. BCG, Bacillus calmette guerin; DTP, diphtheriatetanus-pertussis; Ig, immunoglobulin; Hib, Haemophilus influenzae type b; PS, capsular polysaccharide; Hib PS, Hib capsular polysaccharide vaccine; PRP-T, Hib PS tetanus toxoid conugate vaccine; [...]

There are three conjugate vaccines licensed by the US Food and Drug Administration (FDA) for use against Haemophilus influenzae type b. The American Academy of Pediatrics (AAP) has reviewed and revised its recommendations regarding use of these vaccines based upon two recent studies. The new recommendations suggest that either the HbOC vaccine or the PRP-OMP vaccine (two of the three Haemophilus influenzae vaccines) be given intramuscularly at about two months of age. Either a three-dose series of HbOC or a two-dose series of PRP-OMP should be given with two-month intervals between doses. The same vaccine given initially should be given throughout the period of immunization. A booster dose of HbOC should be given at 15 months of age, or a booster dose of PRP-OMP should be given at 12 months of age. Infants with immunization started between the ages of 7 and 11 months should be given either vaccine in two doses two months apart, and a third dose of the same vaccine at 15 to 18 months. Children between 12 and 14 months of age should be given two doses at two- to three-month intervals. A single dose is sufficient for any child between 15 months and five years of age, and any unimmunized children over five years of age at risk for H. influenzae type b disease should receive a single dose. Any child that had the disease when younger than 24 months of age should be immunized to prevent recurrence. The AAP will release further statements and guidelines regarding this issue in the future. (Consumer Summary produced by Reliance Medical Information, Inc.)

COMMENTARY The introduction and widespread use of Haemophilus influenzae type b (Hib) vaccine has drastically reduced the incidence of bacterial meningitis in children and other invasive infections caused by this [...], One hundred forty-one children of 5 to 59 months of age were immunized with a single intramuscular dose of 0.67, 3.3, 17, or 67 jig polyribophosphate (PRP), the capsular antigen of Hemophilus influenzae, type b. The immunizations were well tolerated, particularly at doses of .67 to 17 µ g. Antibody activity was measured by radioactive antigen binding, using ³H-labelled PRP. Doses of 3.3 and 17 µ g produced significant antibody rises in nearly 90% of recipients; 0.67 and 67 µ g in approximately half. The geometric mean titers were similar at three and six weeks after immunization and were greater with the middle doses. The net antibody increase in responding children was strongly age dependent, but was not related to the pre-immunization antibody concentration. Rises in serum bactericidal activity against H. influenzae type b generally accompanied rises in antibody concentration as measured by the antigen-binding assay. A recently developed Haemophilus influenzae type b capsular polysaccharide vaccine was given to 48 977 children 3 months to 5 years of age; an equal number of children receiving group A meningococcal vaccine served as,controls. The protection as well as serum antibody response was strongly age dependent. Among children who had received the H. influenzae type b vaccine when 18 months of age or older, there were no cases of bacteremic disease caused by H. influenzae type b in the first year after vaccination. At the same time 11 such cases were seen in the control group of the same age, a highly significant difference. In the second year after vaccination two cases occurred in the H. influenzae type b-vaccinated group, five in the meningococcal-group A vaccinated group. No protection was seen among children who had been younger than 18 months when vaccinated, even if they received a booster dose of the vaccine. The serum antibody response to the H. influenzae type b polysaccharide, measured by radioimmunoassay, was poor in children below 18 months of age and good in those above it. No effect of the vaccine could be seen on the nasopharyngeal carriage of H. influenzae type b, which was approximately 6% in this age group. Adverse effects of the vaccine were mild.

Children who have sickle cell disease have an increased risk of infection by certain types of bacteria, known as encapsulated bacteria. This may result from the reduction or complete absence of spleen function. One of the encapsulated bacteria is Hemophilus influenza type b. A vaccine for this pathogen was approved in 1985 for use by asplenic (lacking a functioning spleen) children with sickle cell disease. Little research has been performed to evaluate the safety and effectiveness of this vaccine. This prompted a study which examined the use of this vaccine in 98 sickle cell patients, aged one and one half to 20 years. Overall, the subjects tolerated the vaccine well. Six of the 98 patients developed mild side effects, and one developed more serious symptoms eight hours after receiving the vaccine. The H influenza type b polysaccharide vaccine reliably stimulated immunity in sickle cell patients over age five. However, the vaccine did not consistently protect children under five years against H influenza type b infection. (Consumer Summary produced by Reliance Medical Information, Inc.)

A SYNTHETIC CONJUGATE POLYSACCHARIDE VACCINE AGAINST HAEMOPHILUS INFLUENZAE TYPE B Verez-Bencomo V, Fernandez-Santana V, Hardy E, et al. Science. 2004;305:522-525 Purpose of the Study. To demonstrate the safety and immunogenicity [...]