Protective efficacy of Haemophilus influenzae type b polysaccharide-diphtheria toxoid-conjugate vaccine

We estimated the relative protective efficacy of Haemophilus influenzae type b polysaccharide (PRP) vaccine and PRP-diphtheria toxoid-conjugate (PRP-D) vaccine using data from reports of cases of invasive Haemophilus disease occurring in vaccinated children submitted to the Food and Drug Administration, Rockville, Md, and Washington University, St Louis, Mo. During the first 13 months following licensure of each of the vaccines, there were 127 cases reported in recipients of PRP vaccine vs 17 cases in recipients of PRP-D vaccine. The total number of reported cases for each vaccine is not necessarily comparable, since the extent of vaccine use in the population and the extent of reporting of cases may have been different during the two periods. However, the proportion of reported cases occurring equal to or 14 days or more after vaccination (a period considered sufficient to develop immunity) was significantly greater for PRP vaccine (106 [83%] of 127 cases) compared with PRP-D vaccine (7 [41%] of 17 cases). Based on the ratio of late-onset to early-onset cases observed for PRP vaccine, we would have expected 50 late-onset cases after PRP-D vaccination. Since only 7 late-onset PRP-D vaccine failures were reported (86% fewer than expected), the data suggest that PRP-D vaccine was more effective in preventing disease 14 days or more after vaccination than was PRP vaccine.

Response of preterm infants to diphtheria-tetanus-pertussis vaccine

The American Academy of Pediatrics recommendation that immunization of preterm infants with diphtheria-tetanus-pertussis (DTP) vaccine should begin at 2 months after birth, regardless of gestational age, is based on limited data. A prospective study was conducted to determine the immunogenicity and safety of DTP vaccine in preterm infants. One hundred ten preterm and 146 full term infants received doses of DTP at 2, 4 and 6 months after birth. Adjusted analysis of the antibody responses indicated that after three doses mean titers among preterm infants to each vaccine component were comparable to those of full term infants. Adjusted analysis of the incidence of adverse events indicated that the risk of adverse events in preterm infants was not significantly higher than that in full term infants. DTP vaccine is immunogenic and safe in preterm infants when the series is initiated at 2 months after birth, and this study supports the current recommendation of the American Academy of Pediatrics.

Immunogenicity of the Haemophilus influenzae type b capsular polysaccharide conjugate vaccine in children after systemic Haemophilus influenzae type b infections

We immunized 24 patients (mean age 15.2 +/- 9.3 months) with polyribosylribitol phosphate-diphtheria toxoid conjugate vaccine (PRP-D) 2 months after a systemic Haemophilus influenzae type b infection. Children less than 24 months of age were immunized twice. Serum was obtained for antibody to PRP before and 1 or 2 months after immunization. Three of five children greater than 24 months of age and three of six children 18 to 24 months of age developed greater than 1 microgram/ml of antibody after immunization, and geometric mean postimmunization levels were significantly greater than preimmunization levels for both groups. However, two children who failed to respond to conventional PRP vaccine did not respond as expected to one dose of PRP-D. For children 7 to 17 months of age, the geometric mean PRP antibody levels increased as follows: preimmunization, 0.05 micrograms/ml; after the first dose, 0.28 micrograms/ml (p = 0.003); and after the second dose, 3.39 micrograms/ml (p = 0.001). Of 13 children, 10 developed antibody values greater than 1.0 micrograms/ml. PRP conjugate vaccines are immunogenic in young children who have not developed protective PRP antibody levels after a systemic H. Influenzae type b infection.

The changing epidemiology of diphtheria in Jordan

Outbreaks of diphtheria used to occur regularly in Jordan, the last such outbreak being in 1977-78. Since that time, a massive immunization programme targeted at pre-school-age children has been markedly successful. Hence, when an outbreak of diphtheria occurred in 1982-83, it was unexpected. Of the 35 patients who were treated at the Jordan University Hospital, two died and the remaining 33 recovered uneventfully. Contrary to our findings in previous diphtheria epidemics in Jordan, this outbreak largely involved adolescents and young adults.

Susceptibility to diphtheria in populations vaccinated before and after elimination of indigenous diphtheria in Denmark. A comparative study of antitoxic immunity

The need for routine diphtheria revaccination is still controversial. Only single cases of diphtheria have been observed in Denmark since the mass vaccinations in the 1940s and the introduction of routine vaccination of infants in 1950, despite the fact that general revaccination has not been recommended. An investigation of antitoxin immunity in 1.188 probands 2-69 years of age, randomly or cluster selected, indicated that immunity in the Danish population is still above the limit generally believed to guard against diphtheria epidemics (around 70% being immune in a population). The highest frequency of susceptibility (46%) was found among females 30-39 years of age. Serum antitoxin concentrations in 529 subjects with documentation for complete primary vaccination 1-40 years previously corresponded to a continuous fall-off. Relative to time from vaccination, individuals born when diphtheria occurred frequently in Denmark had significantly higher antitoxin levels than those born later, and among children susceptibility had increased considerably as compared to observations in the 1950s. These phenomena were explained by the effect of natural immune stimulation previously. The present concept of relatively high frequencies of immune subjects also in other western countries may not be valid in the future, when the number of subjects born after the elimination of indigenous diphtheria increases. General revaccinations seem required to maintain herd immunity.

[Diphtheria, an imported disease]

A comparative analysis of 4256 persons living in the Federal Republic of Germany and 4751 applicants for asylum in the FRG allows the conclusion that in the FRG diphtheria is caused by imported toxinogenic strains, originating mostly from developing countries. Since 1975 a total of 109 cases have been observed, 22 ending in death. Such severe cases can be avoided by systematic revaccination even of adults.

Persistence of antibody and response to booster dose of Haemophilus influenzae type b polysaccharide diphtheria toxoid conjugate vaccine in infants immunized at 9 to 15 months of age

At approximately 2 years of age, 27 infants previously immunized at 9 to 15 months of age with two doses of polyribosylribitol phosphate-diphtheria toxoid conjugate vaccine (PRP-D) and 23 infants immunized with polyribosylribitol phosphate (PRP) vaccine were given a single injection of PRP-D. Pre- and post-immunization sera were obtained. No serious local or systemic reactions were observed. The PRP-D recipients had a geometric mean anti-PRP antibody level of 4.8 micrograms/ml 1 month after the second primary injection, retained 1.2 microgram/ml 1 year later, and had a level of 71 micrograms/ml after the booster immunization. In contrast, PRP recipients had a geometric mean level of 0.083 microgram/ml 1 month after the second primary injection, retained 0.042 microgram/ml 1 year later, and after a single dose of PRP-D at approximately 2 years of age had a geometric mean level of 8.6 micrograms/ml. The significantly higher antibody response in the prior PRP-D recipients suggests the recall of immunologic memory induced by the PRP-D vaccine.

Age of diphtheria, tetanus, and pertussis immunization of special care nursery graduates

Diphtheria, tetanus, and pertussis (DTP) immunization data were collected on 103 special care nursery graduates in our neonatal follow-up clinic to determine whether DTP immunization schedules were significantly delayed relative to recommendations of the American Academy of Pediatrics (2, 4, and 6 months for DTP 1, 2, and 3, respectively). An inverse correlation was found between birth weight and immunization for first, second, and third DTP (r = 0.319, P less than .01; r = .205, P less than .05; and r = .236, P less than .05, respectively). We subsequently conducted a mail survey to determine the DTP immunization policy present in effect in 25 neonatal intensive care units in the United States and Canada. The survey indicates that procedural approaches remain markedly heterogeneous, and 10 of 25 (40%) units have no existing policy for implementation of DTP immunization. These data suggest that special care nursery populations are at potential risk for pertussis, which requires a conscious implementation of DTP immunization by the special care nursery, the follow-up clinic personnel, and the primary care physician.

[Phage lysis typing and epidemiology of diphtheria 1975-1984]

Phage typing of the available diphtheria strains from epidemics and isolated diphtheria infections in the Federal Republic of Germany since 1975 showed that the various waves of the disease were caused by pathogenic strains which differed from each other in lysis type and lysogenetic spectrum. The individual regional outbreaks, therefore, were not epidemiologically interlinked. Both a high incidence of diphtheria cases and isolated cases occurring in a particular region and within the same time period, however, were caused by the same pathogen with identical lysis type and lysogenetic pattern. On the other hand, the toxinogenic strains introduced from countries with a high prevalence of the disease had clearly different typing characteristics. According to our present studies on the incidence of pathogen carriers, no toxin-producing diphtheria bacteria are circulating in the indigenous population. It can be assumed, therefore, that the outbreaks of diphtheria during the last few years were caused by such imported strains. Since the importation of toxin-producing diphtheria bacteria is unavoidable and may occur at all times, universal active immunisation in childhood, as well as timely revaccination of adolescents and adults, are mandatory prophylactic measures to prevent new epidemics.

[Importance of vaccination and bacteriological studies in diphtheria epidemics]

The Ouchterlony - Elek gel diffusion test was performed in twenty-nine patients having a positive culture result for diphtheria bacilli on Loeffler and tellurite agars in January and February, 1984 and toxin production was detected in 20 of them. Except one adult patient, the cases ranged in age 2 and 12 years. In 14 patients who have received at least one immunization with diphtheria vaccine had no complication, besides three patients without immunization in whom two received antibiotics plus antitoxin therapy had carditis and soft palate paralysis. Five patients in the non-immunized group and 6 patients in the group received at least one immunization had diphtheritic membrane. In spite of three patients with cardiac and neural complications, with early diagnosis and beginning therapy with antibiotics and antitoxin before the result of in vitro toxigenicity test, O% mortality rate was obtained.