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Research into Haemophilus influenzae, a commensal and pathogen of humans, has resulted in major scientific contributions to biology. The first endonucleases (restriction enzymes), which paved the way for the new genetics, and the DNA used to obtain the first complete genome sequence of a free-living organism were obtained from H. influenzae. Prevention of invasive bacterial infections of infants, such as meningitis, has been achieved using a novel class of vaccines, of which the glycoconjugates of H. influenzae were the first to be licensed. Originally fallaciously proposed to be the aetiological agent of epidemic influenza, now known to be caused by a virus, H. influenzae is a pathogen of global public health importance. Research into the pathogenesis of the infections it causes (for example, meningitis, septicaemia, pneumonia and otitis media) are case studies in understanding the molecular basis of the variation in gene expression and gene sequences that are critical to its commensal and virulence behaviour and for the strategies that can be pursued to prevent H. influenzae diseases through vaccines.

Protein-polysaccharide conjugate vaccines that protect against Haemophilus influenzae type b (Hib), serogroup C Neisseria meningitids, and multiple capsular serotypes of Stretocoiccus pneumoniae have had a major impact on invasive bacterial disease in childhood when incorporated into routine. However, effectiveness data from the UK suggest that primary infant immunization alone might not be associated with long-term protection.

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; [...]

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.

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 [...]

The Chief Medical Officer for Northern Ireland Dr Henrietta Campbell has reminded parents again of the importance of ensuring their children are protected against Haemophilus influenza type B (Hib). All [...]