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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.

Although Haemophilus influenzae type b (Hib) vaccines are effective in preventing the disease in most children, they sometimes fails to prevent infection. When H. influenzae type b polysaccharide (Hib PS) unconjugated vaccine was licensed in 1985, the vaccine was less effective than had been expected based on a study in Finland. At the end of 1987 a conjugate vaccine (combined with a protein to enhance the immune response) combined with diphtheria toxoid (Hib PS-D) was brought to market. Although the new vaccine is highly effective, some children have developed Hib disease in spite of vaccination. To discover why this occurred, 23 patients who developed Hib disease two weeks or more after vaccination were studied. The findings were compared with those from 149 patients who became infected with Hib after vaccination with the unconjugated vaccine, and from 90 unvaccinated patients who also developed the disease. Every one of the children who developed the disease after vaccination with the Hib conjugate vaccine had abnormally low immunoglobulin (Ig) levels, specifically IgG2. From a practical standpoint, this indicates that Ig concentrations, including IgG2, should be measured in all patients, even though they do not have recurrent infections. In addition, children with deficient immune responses should be revaccinated with conjugate vaccine, because they are at increased risk of having a recurrence of the disease. Most children respond to revaccination, and those who do not should be evaluated for therapy for immunodeficiency. (Consumer Summary produced by Reliance Medical Information, Inc.)

ABSTRACT: We evaluated the efficacy of Haemophilus b polysaccharide vaccine in children in Minnesota using a case-control study. The vaccine became available in Minnesota in August 1985. During the subsequent 28 months, 88 cases of invasive H influenzae type b disease were identified in children 24 to 71 months of age, the group targeted for vaccination. Of the 88 cases, 36 (41%) occurred in vaccinated children. Fifty-eight (33%) of 176 controls were vaccinated during a similar period. The vaccine's protective efficacy for children with any history of vaccination was -58% (95% confidence interval =-204%to 18%). The vaccine's protective efficacy for children who were most likely to be protected by vaccination was -55% (95% confidence interval =-238% to 29%). Our results indicate that vaccination with Haemophilus b polysaccharide vaccine had no effect in preventing H influenzae type b disease in Minnesota children.

ABSTRACT: To assess the protective efficacy of the Haemophilus b polysaccharide vaccine, a case-control study was conducted in Connecticut, Dallas County, and greater Pittsburgh. Seventy-six children 24 to 72 months of age who had H influenzae type b isolated from normally sterile sites from August 1985 through July 1987 were enrolled. For each case two controls, matched by age and place of residence, were randomly selected from the records of all live births in the area. Antecedent receipt of the Haemophilus b polysaccharide vaccine was ascertained from the records of all physicians and clinics at which the subjects received medical care. Overall, 12% of the cases and 39% of the controls had received the vaccine. The estimate of the protective efficacy of the vaccine was 88% overall (95% confidence interval, 74% of 96%) and 91% (95% confidence interval, 71% to 99%), 92% (95% confidence interval, 76% to 99%), and 81% (95% confidence interval, 45% to 96%) in Connecticut, Dallas County, and greater Pittsburgh, respectively. The estimates were not substantially affected by adjusting with logistic regression for differences between the cases and controls in race and the attendance of group day care. We conclude that the Haemophilus b polysaccharide vaccine is highly effective in these areas among children who receive the vaccine when they are 24 months of age or older.

ABSTRACT: To assess the efficacy of the Haemophilus b polysacchaide vaccine following licensure and to evaluate the risk of Haemophilus influenzae type b (Hib) disease in the week following vaccination, we conducted a day care--based case-control efficacy study using cases of invasive Hib disease ascertained through active surveillance in areas with a total population of 34 million. For each patient 18 to 59 months old, up to three 18- to 59-month-old controls were chosen from the same day care classroom. Using conditional logistic regression, the vaccine efficacy was estimated to be 45% (95% confidence interval = - 1% to 70%) and did not change significantly after accounting for potential biases. In addition, three (3%) of 104 patients vs five (2%) of 207 controls were vaccinated within seven days before the patients' dates of admission (odds ratio = 1.8, 95% confidence interval=0.3 to 10.2), which does not suggest an increased risk of Hib disease in the week following immunization. This study suggests that the efficacy of the currently used HBPV is less than expected from previous studies and points out the usefulness of case-control studies for monitoring vaccine efficacy following licensure.