Immunogenicity and safety of Haemophilus influenzae type b-tetanus protein conjugate vaccine alone or mixed with diphtheria-tetanus-pertussis vaccine in infants

Hib antibody responses in infants following diphtheria, tetanus, acellular pertussis, and conjugated Haemophilus influenzae type b (Hib) combination vaccines with decreasing amounts of tetanus toxoid

BACKGROUND

While combination vaccines have contributed to improved vaccine uptake rates in children, studies have documented varied immunogenicity to specific vaccine components. We studied whether varying the amount of tetanus toxoid (TT) in a DTaP and Hib combination vaccine would result in immunogenicity comparable with separate, concurrent administration.

METHODS

We evaluated the immunogenicity of Massachusetts Biologic Laboratories (MBL) diphtheria, tetanus, and acellular pertussis (mDTaP) vaccine combined with tetanus-conjugated MBL Haemophilus influenzae type b vaccine (mHib) in a single injection (DTaPH). We compared four DTaPH vaccines containing varying concentrations of TT. We also evaluated the immune response to the DTaP vaccine manufactured by Connaught Laboratories (now known as Sanofi Pasteur) given with mHib and with Wyeth Hib-CRM₁₉₇ (HbOC) as separate injections. Vaccines were administered to 240 healthy infants at 2, 4, and 6 months of age, and blood specimens for antibody determination were obtained before each immunization and one month after the third immunization.

RESULTS

We found no significant differences in immune response to the vaccines between the four DTaPH groups. Hib antibody responses were similar in the mHib and the HbOC groups but significantly lower in the DTaPH groups, as measured by Chinese Hamster Ovary (CHO) cell neutralization titers and filamentous hemagglutinin antigen (FHA) geometric mean concentrations (GMC) of anti-Hib antibodies. There were no significant differences between the groups in pertussis or tetanus toxoid antibody levels.

CONCLUSION

Reducing tetanus toxoid amounts did not produce comparable immunogenicity for Hib. The nature of the interaction between immune responses to DTaPH components should be explored further to enable the development of better Hib-containing combination vaccines.

A randomized, open-label clinical trial to evaluate immunogenicity and safety of an indigenously developed DTwP-Hib tetravalent combination vaccine (Easyfour®-TT) with Quadrovax® in Indian infants

An open-label, randomized, multi-center trial was conducted to compare the immunogenicity and safety of an indigenously developed tetravalent DTwP-Hib vaccine, Easyfour®-TT with a commercially available vaccine, Quadrovax®. A total of 244 infants in good health, aged 6-10 weeks, were randomized in a 1:1 allocation to receive three doses of the test or comparator vaccine. Immunogenicity of the vaccines was determined by measuring the baseline and post-vaccination antibody response against the vaccine antigens; safety was evaluated in terms of local and systemic reactions (solicited and unsolicited) reported during the trial. Similar levels of seroprotection/seroresponse were achieved, 4 weeks after receiving 3 doses of Easyfour®-TT and Quadrovax®, and the antibody response of Easyfour®-TT was found non-inferior to Quadrovax®, against all four vaccine antigens. Both vaccines were well tolerated and had similar reactogenicity profiles, with a significantly lower occurrence of local (redness at injection site) and systemic reactions (irritability post-vaccination) with Easyfour®-TT vaccine as compared to Quadrovax® (p < 0.05). All adverse events resolved completely with no sequelae. All through the study, only one serious adverse event was observed that completely resolved upon treatment and was deemed unrelated to the vaccine administered. This study demonstrated that Easyfour®-TT vaccine was safe and immunogenic.

CLINICAL TRIAL REGISTRATION NUMBER

CTRI/2014/12/005326 (registered with the Clinical Trial Registry of India (CTRI)).

A gold nanoparticle-linked glycoconjugate vaccine against Burkholderia mallei

Burkholderia mallei are Gram-negative bacteria, responsible for the disease glanders. B. mallei has recently been classified as a Tier 1 agent owing to the fact that this bacterial species can be weaponised for aerosol release, has a high mortality rate and demonstrates multi-drug resistance. Furthermore, there is no licensed vaccine available against this pathogen. Lipopolysaccharide (LPS) has previously been identified as playing an important role in generating host protection against Burkholderia infection. In this study, we present gold nanoparticles (AuNPs) functionalised with a glycoconjugate vaccine against glanders. AuNPs were covalently coupled with one of three different protein carriers (TetHc, Hcp1 and FliC) followed by conjugation to LPS purified from a non-virulent clonal relative, B. thailandensis. Glycoconjugated LPS generated significantly higher antibody titres compared with LPS alone. Further, they improved protection against a lethal inhalation challenge of B. mallei in the murine model of infection.

FROM THE CLINICAL EDITOR

Burkholderia mallei is associated with multi-drug resistance, high mortality and potentials for weaponization through aerosol inhalation. The authors of this study present gold nanoparticles (AuNPs) functionalized with a glycoconjugate vaccine against this Gram negative bacterium demonstrating promising results in a murine model even with the aerosolized form of B. Mallei.

Mechanisms of aluminum adjuvant toxicity and autoimmunity in pediatric populations

Immune challenges during early development, including those vaccine-induced, can lead to permanent detrimental alterations of the brain and immune function. Experimental evidence also shows that simultaneous administration of as little as two to three immune adjuvants can overcome genetic resistance to autoimmunity. In some developed countries, by the time children are 4 to 6 years old, they will have received a total of 126 antigenic compounds along with high amounts of aluminum (Al) adjuvants through routine vaccinations. According to the US Food and Drug Administration, safety assessments for vaccines have often not included appropriate toxicity studies because vaccines have not been viewed as inherently toxic. Taken together, these observations raise plausible concerns about the overall safety of current childhood vaccination programs. When assessing adjuvant toxicity in children, several key points ought to be considered: (i) infants and children should not be viewed as “small adults” with regard to toxicological risk as their unique physiology makes them much more vulnerable to toxic insults; (ii) in adult humans Al vaccine adjuvants have been linked to a variety of serious autoimmune and inflammatory conditions (i.e., “ASIA”), yet children are regularly exposed to much higher amounts of Al from vaccines than adults; (iii) it is often assumed that peripheral immune responses do not affect brain function. However, it is now clearly established that there is a bidirectional neuro-immune cross-talk that plays crucial roles in immunoregulation as well as brain function. In turn, perturbations of the neuro-immune axis have been demonstrated in many autoimmune diseases encompassed in “ASIA” and are thought to be driven by a hyperactive immune response; and (iv) the same components of the neuro-immune axis that play key roles in brain development and immune function are heavily targeted by Al adjuvants. In summary, research evidence shows that increasing concerns about current vaccination practices may indeed be warranted. Because children may be most at risk of vaccine-induced complications, a rigorous evaluation of the vaccine-related adverse health impacts in the pediatric population is urgently needed.

Response and persistence of antibodies to PRP-T and DTwP vaccines with concomitant administration of conjugate vaccines

We first studied the immunogenicity of PRP-T and DTwP vaccines in Filipino infants given at 6, 10 and 14 weeks concomitantly with either an aluminum adjuvanted eleven-valent pneumococcal conjugate vaccine (11PncTD) or a meningococcal diphtheria-conjugated vaccine as compared to a control group that received only DTwP/PRP-T. The GMCs and proportions of infants achieving protective antibody concentrations to DTwP and PRP-T vaccine antigens were similar among the groups. In the second phase, the control group received 11PncTD at 18 weeks and the antibody concentrations were measured at 9 months in all children; 11PncTD induced a booster response to diphtheria in the control group. There was no negative interference from concomitant administration of new conjugate vaccines. In contrast, 11PncTD can boost the antibody response to the carrier proteins.

Combination conjugate vaccines

Increasingly, more diseases are becoming vaccine preventable, but maintaining community and provider acceptance demands that the number of injections does not increase. Combination conjugate vaccines represent an inevitable and important advance. This paper reviews the efficacy and safety of combination conjugate vaccines, including immunological mechanisms underlying interactions among vaccine epitopes, the role of immunological memory, and correlates of immunity. Specific attention is given to the experience with combination vaccines against each of Haemophilus influenzae type b, Streptococcus pneumoniae and Neisseria meningitidis. The implications of these findings for different communities are discussed, key areas for further research identified and implications for post-licensure monitoring addressed.

Physico-chemical and immunological examination of the thermal stability of tetanus toxoid conjugate vaccines

The thermal stability of meningococcal C (MenC)- and Haemophilus influenzae b (Hib)-tetanus toxoid (TT) conjugate vaccines was investigated using spectroscopic and chromatographic techniques and immunogenicity assays in animal models. In this stability study, both the bulk concentrate and final fills were incubated at -20, 4, 23, 37 or 55 degrees C for 5 weeks or subjected to cycles of freeze-thawing. The structural stability, hydrodynamic size and molecular integrity of the treated vaccines were monitored by circular dichroism (CD), fluorescence and nuclear magnetic resonance (NMR) spectroscopic techniques, size exclusion chromatography (FPLC-SEC), and high performance anion exchange chromatography coupled with pulsed amperometric detection (HPAEC-PAD). Only storage at 55 degrees C for 5 weeks caused some slight unfolding and modification in the tertiary structure of the carrier protein in the MenC-TT conjugate. Substantial loss of saccharide content from the MenC conjugates was observed at 37 and 55 degrees C. Unexpectedly, the experimental immunogenicity of MenC-TT vaccine adsorbed to Alhydrogel was significantly reduced only by repeated freeze-thawing, but not significantly decreased by thermal denaturation. Neither the molecular integrity nor the immunogenicity of the lyophilised Hib-TT vaccines was significantly affected by freeze-thawing or by storage at high temperature. In conclusion, the MenC- and Hib-TT conjugate vaccines were relatively stable when stored at higher temperatures, though when MenC-TT vaccine was adsorbed to Alhydrogel, it was more vulnerable to repeated freeze-thawing. When compared with CRM(197) conjugate vaccines studied previously using similar techniques, the tetanus toxoid conjugates were found to have higher relative thermal stability in that they retained immunogenicity following storage at elevated temperatures.

Associated or combined vaccination of Brazilian infants with a conjugate Haemophilus influenzae type b (Hib) vaccine, a diphtheria-tetanus-whole-cell pertussis vaccine and IPV or OPV elicits protective levels of antibodies against Hib

This study investigated the immunogenicity and safety of including a Haemophilus influenzae type b vaccine (polyribosylribitol phosphate conjugated to tetanus toxoid, PRP-T) in three different vaccination schemes: (1) PRP-T reconstituted with a combined diphtheria-tetanus-pertussis-inactivated poliovirus vaccine (DTP-IPV//PRP-T); (2) PRP-T reconstituted with DTP and administered concomitantly with an oral poliovirus vaccine (DTP//PRP-T+OPV); and (3) PRP-T administered concomitantly with DTP at a different injection site and OPV (DTP+PRP-T+OPV). Vaccines were given at 2, 4, and 6 months of age. A total of 252 infants were enrolled, and randomly assigned to one of the three vaccination groups (84 infants in each group); 241 infants were followed until the end of the study. Antibody production against PRP, diphtheria, tetanus and pertussis antigens was satisfactory for each vaccination scheme used. A good response to Hib vaccine was elicited in each group, and 3 months after the third vaccine dose, at least 97% of children in each group had levels of PRP antibody considered to be seroprotective (>0.15 microg/ml), and over 90% of children in each group had levels over 1. 0 microg/ml. The solicited local and systemic adverse events following vaccination were mild in all groups and resolved within 4 days without medical intervention. With the exception of fever, which was more common after the second dose in children who received DTP-IPV//PRP-T, local and systemic reactions did not differ between the vaccination groups. Due to the practical advantages of combined vaccines, their use in routine immunization programs in developing countries is highly desirable. Our results show that Hib conjugate vaccine can be included in routine immunization programs that include either OPV or IPV with satisfactory immunogenicity and safety profiles. This flexible approach should facilitate the inclusion of the Hib conjugate vaccine in routine immunization programs on a world-wide scale.

New combination vaccines

Physicians can achieve full vaccination at each of the recommended visits by administering three or four injections, but for infants, four injections seem to be a maximum in light of the size of the infant thigh, which is the preferred injection site. Thus, physicians must make room for all of the new vaccines on the horizon. To accomplish that task, combinations will be necessary. Progress toward that goal is occurring.

Epidemiology of Haemophilus influenzae type b meningitis in Manila, Philippines, 1994 to 1996

BACKGROUND

Effective vaccines against Haemophilus influenzae type b (Hib) have shown impressive results in decreasing Hib meningitis in developed countries. In the Philippines Hib vaccines are not part of the routine immunization given to children. Before a decision can be made to include Hib vaccines in immunization program, epidemiology of Hib meningitis in Manila, Philippines, should first be described.

METHODOLOGY

A cohort of 41,592 children <5 years of age in Central Manila was the study population. Confirmed cases between January, 1994, and December, 1996, were obtained from all hospitals in the region. Confirmation of cases was based on positive culture isolated from blood or cerebrospinal fluid (CSF) or Hib antigen identified in CSF with a clinical diagnosis of Hib meningitis. The progress of children with Hib meningitis postinfection was evaluated from hospital records.

RESULTS

There were 118 episodes of Hib meningitis identified in the population in the study period. Sequelae occurred in 15% of the total cases, and the case fatality rate was 11%. The annual incidence of Hib meningitis in Manila for children <5 years old was 95 per 100,000.

CONCLUSIONS

Hib meningitis in Central Manila is common. The incidence is particularly high in children <6 months old. Adverse neurologic outcomes and a high case fatality rate in children younger than 1 year suggest that a vaccination program would be useful.

Combined vaccination of Haemophilus influenzae type b conjugate and diphtheria-tetanus-pertussis containing acellular pertussis

After the introduction of effective Haemophilus influenzae type b (Hib) conjugate vaccines, clinical practice has driven the development of combination vaccines comprising Hib conjugates with the infant diphtheria-tetanus-pertussis (DTP) vaccines. However, when such combinations contain an acellular pertussis component (Pa), the antibody response to Hib is lower than that with separate injections and doubts have been raised about their efficacy. We believe that such concerns are unwarranted, since the serological correlates of efficacy previously applied for Hib polysaccharide vaccines seem inappropriate for Hib conjugates. Furthermore, our own studies have shown that the lower antibody responses are not associated with impaired function of the antibodies induced, nor, and possibly more importantly, with the induction of immune memory against Hib. Therefore, with the proviso that careful clinical surveillance of Hib disease is maintained, we encourage the introduction of DTPa-Hib combinations to facilitate the inclusion of Hib into the already crowded childhood immunisation schedule.

The effect of reconstitution of an Haemophilus influenzae type b-tentanus toxoid conjugate (PRP-T) vaccine on the immune responses to a diphtheria-tetanus-whole cell pertussis (DTwP) vaccine: a five-year follow-up

Controversial results have been obtained from previous studies on the combined administration of Haemophilus influenzae type b-tetanus toxoid conjugate (PRP-T) and diphtheria-tetanus-whole-cell pertussis (DTwP) combination vaccines, with regard to possible reciprocal interference between the constituent antigens. To document the priming effect and possible long-term immunogenic interference of PRP-T and DTwP combination vaccines, a randomized, double-blind, controlled study was conducted in Belgium. A total of 168 healthy infants received, at 3, 4 and 5 months of age, DTwP vaccine mixed just prior to injection either with PRP-T vaccine (group A, DTwP//PRP-T, N = 85) or with placebo (group B, DTwP//Placebo, N = 83). At the age of 14 months, children of both groups were randomized to receive either a dose of DTwP//PRP-T vaccine (subgroups A1 and B1) or a dose of Hib polysaccharide (PRP) vaccine (subgroups A2 and B2). Those children in subgroups A1 and B1 had an additional serum sample taken at the age of 5 years (at the time of a DT booster). The immune response to Hib polysaccharide at the age of 4, 5 and 6 months confirmed the excellent immunogenicity profile of PRP-T in infants. In addition, the vigorous anamnestic response (i.e. a 20-fold increase of GMT) to a booster dose of the plain capsular polysaccharide (PRP) reflected the efficient Hib-priming induced by the combined DTwP//PRP-T vaccine. Reconstitution of PRP-T with DTwP did not affect the immune response to diphtheria toxoid or pertussis agglutinins. Nevertheless, at almost any time point during the five-year follow-up, the tetanus antitoxin GMT values were significantly lower in the DTwP//PRP-T group (A and A1) than in the DTwP//Placebo group (B and B1). Despite the suppressive effect on GMT values, intergroup differences in rates of seroprotection were never significant, except after doses 2 and 3 for which there were lower percentages of children in group A with antitoxin titers > 0.05 IU/mL and > 1.0 IU/mL. In the group primed with the combined DTwP//PRP-T vaccine, (1) a DT booster dose at the age of 5 years provoked a 150-fold increase in tetanus antitoxin GMT, (2) a high tetanus antitoxin GMT value was attained (GMT = 19.3 IU/mL) and (3) all children in this group had tetanus antitoxin titers > 1.0 IU/mL, so it may be concluded that all these children will still be protected against tetanus until at least the age of the next recommended booster dose (i.e. the age of 15 years). No differences in the occurrence of adverse events were observed between the groups who received the DTwP//PRP-T vaccine or the DTwP//Placebo vaccine, both vaccines being associated with events customarily attributable to DTwP (data not shown). Our results indicate (1) that the combination vaccine, DTwP//PRP-T, represents a safe and effective alternative for the existing uncombined vaccines and (2) that the long-term effect of interference between the components of future combination vaccines should be studied with subsequent booster doses, followed by the evaluation of persistence of antibodies over several years.

Evaluation of a guinea pig model to assess interference in the immunogenicity of different components of a combination vaccine comprising diphtheria, tetanus and acellular pertussis (DTaP) vaccine and haemophilus influenzae type b capsular polysaccharide conjugate vaccine

A guinea pig model to assess the immunogenicity of a combination vaccine containing diphtheria, tetanus and acellular pertussis (DTaP) vaccine and Haemophilus influenzae type b (Hib) capsular polysaccharide conjugated to tetanus toxoid (HibT) was evaluated comparatively with the mouse immunogenicity test to study the effect of combining these antigens on the immunogenicity of various components. The immunogenicity test in mice was performed by subcutaneous injection of groups of 10 animals twice at an interval of four weeks with 1/10 of a single human dose of various formulations of combination vaccines, DTaP or HibT vaccine. The animals were bled at 4 and 6 weeks and IgG or total antibodies to various components were determined by ELISA or RIA. The guinea pig immunogenicity model included groups of animals injected subcutaneously twice at an interval of six weeks with 1.5 times the single human dose of various formulations. The animals were bled at 4, 6 and 8 weeks and serum samples were tested for antibodies to various components by ELISA, RIA and/or neutralization tests. Additionally, potency of tetanus and diphtheria components was assessed as per the US Food and Drug Administration's regulations. Aluminium phosphate (AIPO(4)) adsorbed HibT vaccine or HibT as a combination with AIPO(4)adsorbed DTaP vaccine showed significant increases in IgG antibodies to tetanus toxin in mice as well increased tetanus antitoxin levels in guinea pigs as compared to soluble HibT vaccine. In general, combining DTaP and HibT vaccines did not affect the antibody levels to tetanus and diphtheria toxoids whereas DTaP-HibT combination vaccine elicited significantly lower IgG antibodies to pertussis toxin and filamentous haemagglutinin than DTaP vaccine alone, particularly after first injection. Mice showed similar Hib antibody responses for the combination and HibT alone whereas guinea pigs consistently showed lower anamnestic responses to Hib for combination formulations than for HibT alone. Reducing the amount of HibT and/or tetanus toxoid in the combination formulations reduced this suppression of Hib antibody response in guinea pigs. Suppression of Hib antibody response in combination vaccines has also been reported from recent clinical trials. Based on the results from this study, it appears that the guinea pig model may be able to predict the human response to various components of combination vaccines.

Effect of combination with an acellular pertussis, diphtheria, tetanus vaccine on antibody response to Hib vaccine (PRP-T)

Acellular pertussis vaccines provide protection against whooping cough with few adverse effects. Their introduction to routine immunisation programmes would be facilitated by their incorporation with other routinely administered vaccines. 262 infants were immunised with an acellular pertussis vaccine containing pertussis toxin and filamentous haemagglutinin, combined with diphtheria and tetanus toxoids. This vaccine was mixed with Haemophilus influenzae type b tetanus toxoid vaccine (PRP-T) so that infants received a single injection at age 2, 3 and 4 months. One month after the third dose the geometric mean titre of Hib IgG antibody was 0.48 microgram ml-1. Eighty-two percent of infants achieved a titre of 0.15 microgram ml-1, with only 27% achieving 1.0 microgram ml-1. This combination vaccine induced low Hib antibody responses when compared to other studies in which PRP-T was mixed with acellular or whole-cell pertussis vaccines. The combined vaccine did, however, appear to prime a subset of 35 infants for response to a fourth dose of PRP-T at 13 months of age, with a rise in GMT from 0.21 microgram ml-1 to 36.6 micrograms ml-1. These data have important implications for the introduction of combination acellular pertussis vaccines.

Safety and immunogenicity of a combined pentavalent diphtheria, tetanus, acellular pertussis, inactivated poliovirus and Haemophilus influenzae type b-tetanus conjugate vaccine in infants, compared with a whole cell pertussis pentavalent vaccine

BACKGROUND

We compared the safety and immunogenicity of two combined diphtheria-tetanus-pertussis-inactivated poliovirus vaccines containing either acellular (Pa, SmithKline Beecham Biologicals) or whole cell (Pw, Pasteur Merieux Connaught) pertussis components, mixed with a Haemophilus influenzae type b polysaccharide polyribosylribitol phosphate-tetanus conjugate vaccine in an open, randomized study in healthy infants.

DESIGN

The combined vaccines were given at 2, 4, 6 and 12 months of age, and serum samples were obtained at ages 2, 6, 7, 12 and 13 months. Adverse events were obtained by diary cards.

RESULTS

The Pa group (n = 101) had a clearly lower incidence of both local and systemic adverse events than the Pw group (n = 100). Immunogenicity was comparable for the diphtheria and tetanus components, but significantly superior for pertussis toxin, filamentous hemagglutinin, pertactin and polioviruses 1, 2 and 3 in the Pa group. Both groups had an appropriate response with regard to H. influenzae type b polysaccharide polyribosylribitol phosphate, but the dynamics of the response were significantly different: geometric mean concentrations (micrograms per ml) after the second, third and booster doses were 1.27, 5.06 and 23.12 in the Pa group and 2.72, 6.66 and 13.59 in the Pw group, respectively (P = 0.0002 after second dose; P = 0.0005 after booster).

CONCLUSION

The presently studied diphtheria, tetanus, acellular pertussis-H. influenzae b vaccine conjugated to tetanus toxoid combination was at least as immunogenic as the diphtheria, tetanus, whole cell pertussis-H. influenzae b vaccine conjugated to tetanus toxoid combination, with a significantly better safety profile. This is of obvious importance in countries where inactivated poliovirus vaccine is part of the routine infant immunization programs.

Vaccine antigen interactions after a combination diphtheria-tetanus toxoid-acellular pertussis/purified capsular polysaccharide of Haemophilus influenzae type b-tetanus toxoid vaccine in two-, four- and six-month-old infants

OBJECTIVE

The safety and immunogenicity of a diphtheria-tetanus toxoid-acellular pertussis vaccine (DTaP; Trepedia)/Haemophilus influenzae b polysaccharide (PRP-T; ActHib) combined vaccine (TriHibir; Pasteur Mérieux Connaught) was compared with DTaP and PRP-T given at the same visit but at separate sites in a prospective multicenter, open label trial.

METHODS

Infants were randomized to four groups (three consistency lots of DTaP/PRP-T vs. one of the consistency lots given as separate vaccines); injections were administered at 2, 4 and 6 months of age. Pre-Dose 1 and post-Dose 3 sera were assayed for antibody titers against all antigens. Reactions to the vaccinations were assessed by parent questionnaire for 30 days after each injection visit.

RESULTS

Four hundred eighty-five infants were enrolled; 296 evaluable infants were included in the DTaP/PRP-T group compared with 70 infants in the DTaP and PRP-T vaccine group. Infants who received the combined vaccine had higher post-Dose 3 geometric mean antibody titers to diphtheria antitoxin (P < 0.01) and pertussis filamentous hemagglutinin (P < 0.05) and lower geometric mean antibody titers to tetanus antitoxin (P < 0.05) and Haemophilus influenzae b (Hib) polysaccharide (PRP) (P < 0.05). The geometric mean anti-PRP antibody titer in the DTaP/PRP-T group was 4.3 micrograms/ml compared with 7.0 micrograms/ml in the separate vaccine group (P < 0.05), and the percentage of infants with antibody titers > or = 0.15 and 1 microgram/ml were, respectively, 95 and 86%, whereas they were 100% for both titers in the separate vaccines group. DTaP/ PRP-T vaccine given concomitantly or 1 month apart from hepatitis B vaccine and oral poliomyelitis vaccine caused no significant differences in immunogenicity or safety. The safety assessments for the DTaP/PRP-T vaccine showed no consistent differences in systemic or local injection site reactions compared with DTaP and PRP-T administered separately.

CONCLUSION

Although the antibody responses to tetanus and Hib polysaccharide in the evaluated DTaP/PRP-T combined vaccine were significantly lower than those seen after separate DTaP and PRP-T administration, the combined vaccine elicited an immune response against diphtheria, tetanus, pertussis and Haemophilus influenzae b likely to confer protection.

Immunogenicity and safety of a liquid combination of DTP-PRP-T [corrected] vs lyophilized PRP-T reconstituted with DTP

The immunogenicity and safety of a combined diphtheria, tetanus, pertussis and Haemophilus influenzae type b-tetanus conjugate vaccine (DTP-PRP-T) was compared to the same combination obtained by the reconstitution of H. influenzae type b-tetanus conjugate vaccine lyophilized (PRP-T) with liquid diphtheria-tetanus-pertussis vaccine (DTP). Two hundred and sixty-two healthy infants were randomized to receive a intramuscular injection of 0.5 ml of one of the above combination vaccines at 2, 4 and 6 months of age, and a subgroup of 134 infants received a booster dose at 12 months. Serum antibody levels to each vaccine component were measured at ages 2, 6, 7, 12 and 13 months. Systemic and local reactions were assessed during the first 3 days after each injection by diary cards distributed to the parents. After the third dose and booster administered at 12 months of age, significant equivalence between the groups was observed, and the geometric mean titer of anti H. influenzae type b capsular polysaccharide (Hib-CP) antibodies were 5.9 and 32.6 micrograms ml-1 for the liquid combination group and 5.8 and 19.4 for the lyophilized group, respectively. After the third dose, anti-Hib-PC antibody levels of > or = 1.0 microgram ml-1 and 0.15 microgram ml-1 were seen in 94% and 100%, respectively, of the liquid combination group and 90 and 99%, respectively of the lyophilized group. After the booster dose, levels of > or = 1.0 microgram ml-1 were observed in 100% and 93.5% of the liquid combination group and the lyophilized combination group, respectively. Systemic and local reactions to the vaccination were generally mild and did not differ significantly between the groups. We conclude that the liquid combination of DTP-PRP-T is safe and at least as immunogenic as the lyophilized preparation. This liquid preparation, like other combined vaccines may be helpful for planning vaccination programs with a reduced number of injections.

Randomised trial of the effect of co-administration with acellular pertussis DTP vaccine on immunogenicity of Haemophilus influenzae type b conjugate vaccine

BACKGROUND

Inclusion of new vaccines in vaccination programmes for children would be easier if they could be combined with existing vaccines. Vaccines containing acellular pertussis in the diphtheria/tetanus/pertussis (DTP-a) combination are expected to replace the conventional whole-cell vaccines (DTP-w). We tested the immunogenicity and safety of a combination of DTP-a with the Haemophilus influenzae type b (Hib) conjugate of Hib capsular polysaccharide and tetanus toxid (PRP-T), and inactivated poliovirus vaccine (i.p.v.).

METHODS

120 infants were enrolled and randomised to four groups to receive DTP-a at ages 2, 4, and 6 months. At 4 and 6 months they also received Hib conjugate and i.p.v., either as separate injections or mixed with DTP-a. All injections were given intramuscularly in the anterolateral area of the thigh. Any reactions after each vaccination were noted by the parents. EIA was used to measure titres of diphtheria, tetanus, and pertussis antibodies, RIA for Hib anticapsular antibodies, and microneutralisation assay for poliovirus antibodies from serum samples collected at the ages of 2, 4, 6, and 7 months.

FINDINGS

There were 30 infants in each group. Only mild adverse events were reported. There was a tendency towards slightly lower concentrations of filamentous haemagglutinin, tetanus, and poliovirus 1 antibodies when the vaccines were mixed. However, there was a more pronounced difference (p = 4 x 10(-6)) in Hib antibodies between groups receiving Hib capsular polysaccharide mixed with DTP-a (geometric mean concentrations 0.37 microgram/mL and 0.56 microgram/mL) compared with groups receiving the vaccines separately (3.10 micrograms/mL and 3.94 micrograms/mL).

INTERPRETATION

Administration of premixed DTP-a, Hib conjugate, and i.p.v. affect the immune response significantly. The mechanism of this interference is not clear. The immunogenicity of all antigens must be tested before new combinations can be accepted for vaccination programmes for infants.

Combined diphtheria, tetanus, pertussis, and Haemophilus influenzae type b vaccines for primary immunisation

A total of 146 infants were immunised at ages 2, 3, and 4 months with a combined diphtheria, tetanus, pertussis (DTP)--Haemophilus influenzae type b (Hib) tetanus toxoid conjugate (PRP-T) vaccine (Pasteur Merieux) to assess the antibody response and adverse events associated with immunisation. Adverse events, including fever, were recorded by parents in a diary for three days following each injection. Blood was taken before the first immunisation and four weeks after the third immunisation to assess antibody response. Data were compared with those from historical controls who had received DTP and PRP-T vaccines by separate injection. The combined vaccine was well tolerated. Rates of local and general reactions were similar to those reported for infants immunised by separate injection. All infants achieved protective antibody titres (> 0.01 IU/ml) for diphtheria and tetanus; 98% acquired Hib (PRP) antibody > 0.15 microgram/ml and 82.5% > 1.0 microgram/ml. Pertussis antibody titres (pertussis toxin, filamentous haemagglutinin, total agglutinins, and agglutinins 2 and 3) showed appreciable rise following immunisation. DTP and PRP-T vaccines provide similar antibody responses and adverse effects whether mixed in the same syringe or administered by separate injection. The vaccines could be combined for use in the United Kingdom primary immunisation schedule.

Priming with diphtheria-tetanus-pertussis vaccine enhances the response to the Haemophilus influenzae type b tetanus conjugate vaccine in infancy

Haemophilus influenzae type b (Hib) capsular polysaccharide (PS) conjugated to tetanus toxoid (PRP-T) was given at 4 and 6 months of age and anti-Hib PS antibody response to the first and second dose of PRP-T was compared in groups that received diphtheria-tetanus-pertussis (DTP) vaccine either simultaneously with PRP-T (34 infants) or separately at 3, 4 and 5 months of age (49 infants). The geometric mean anti-Hib PS antibody concentration after the first dose of PRP-T given at 4 months of age was eightfold higher if the infants primed with DTP at 3 months of age than if the first dose of DTP was given together with the first dose of PRP-T (0.81 microgram ml-1 vs 0.11 microgram ml-1). The positive influence of DTP priming was seen also after the second dose of PRP-T given at 6 months of age (7.55 micrograms ml-1 vs 3.45 micrograms ml-1).

Comparison of five different vaccination schedules with Haemophilus influenzae type b-tetanus toxoid conjugate vaccine

OBJECTIVE

To compare seroresponses to five different vaccination schedules for Haemophilus influenzae type b (Hib)-tetanus toxoid conjugate (PRP-T) vaccine in infants.

DESIGN

Four different two-dose schedules were compared, with doses given at 1 and 3 months, 2 and 4 months, 2 and 6 months, or 4 and 6 months of age. One group received three doses at 2, 4, and 6 months of age. The PRP-T vaccine was given in the same syringe with diphtheria-tetanus-pertussis (DTP) vaccine; inactivated polio vaccine (IPV) was given in a separate syringe. Anti-Hib polysaccharide antibodies were measured by radioimmunoassay in sera taken before each immunization, 1 month after the second dose, at 7 and at 12 to 24 months of age.

SUBJECTS

A total of 196 healthy infants were enrolled between November 1990 and November 1992.

RESULTS

After one dose of PRP-T there were no significant differences in geometric mean antibody concentrations (0.09 to 0.13 microgram/ml) or in fold responses among the schedules. The response to the second dose was significantly higher than the response to the first dose given at the same age. The geometric mean antibody concentration was lower in the group vaccinated at 1 and 3 months than in the groups vaccinated at 2 and 4 months, 2 and 6 months, or 4 and 6 months. The three-dose schedule resulted in a significantly higher final antibody concentration than the best two-dose schedule (p <0.001). In most children (64% to 93%), the antibody concentration remained at least 0.15 microgram/ml up to the age of 12 to 24 months.

CONCLUSIONS

The Hib conjugate vaccine, PRP-T, administered concomitantly with DTP vaccine and IPV, was immunogenic with schedules starting at 1 to 4 months of age. Two injections of PRP-T vaccine were immunogenic enough to maintain protection up to 12 to 18 months of age.

A controlled trial of two acellular vaccines and one whole-cell vaccine against pertussis. Progetto Pertosse Working Group

BACKGROUND

Concern about both safety and efficacy has made the use of whole-cell pertussis vaccines controversial. In some European countries, including Italy, the rate of vaccination against pertussis is low.

METHODS

We conducted a double-blind trial in Italy in which infants were randomly assigned to vaccination at two, four, and six months of age with an acellular pertussis vaccine together with diphtheria and tetanus toxoids (DTP); a DTP vaccine containing whole-cell pertussis (manufactured by Connaught Laboratories); or diphtheria and tetanus toxoids without pertussis (DT). The acellular DTP vaccine was either one containing filamentous hemagglutinin, pertactin, and pertussis toxin inactivated with formalin and glutaraldehyde (SmithKline Beecham) or one with filamentous hemagglutinin, pertactin, and genetically detoxified pertussis toxin (Chiron Biocine). Pertussis was defined as 21 days or more of paroxysmal cough, with infection confirmed by culture or serologic testing.

RESULTS

The efficacy of each vaccine, given in three doses, against pertussis was determined for 14,751 children over an average of 17 months, with cases included in the analysis if cough began 30 days or more after the completion of immunization. For both of the acellular DTP vaccines, the efficacy was 84 percent (95 percent confidence intervals, 76 to 89 percent for Biocine DTP and 76 to 90 percent for SmithKline DTP), whereas the efficacy of the whole-cell DTP vaccine was only 36 percent (95 percent confidence interval, 14 to 52 percent). The antibody responses were greater to the acellular vaccines than to the whole-cell vaccine. Local and systemic adverse events were significantly more frequent after the administration of the whole-cell vaccine. For the acellular vaccines, the frequency of adverse events was similar to that in the control (DT) group.

CONCLUSIONS

The two acellular DTP vaccines we studied were safe, immunogenic, and efficacious against pertussis, whereas the efficacy of the whole-cell DTP vaccine was unexpectedly low.

Haemophilus influenzae: then and now

Haemophilus influenzae has long been recognised as a major cause of serious infection and mortality in children less than 5 years old. Prior to the introduction of Haemophilus influenzae type b (Hib) immunisation, the incidence of a child suffering an invasive Haemophilus infection was 20-50/100,000 in industrialised countries and up to ten times higher in developing regions. The introduction of a Hib vaccine programme results in a rapid and dramatic decline in the incidence of Hib infection in the susceptible childhood population. For example, within two years of the introduction of routine Hib vaccination of infants in the UK, the risk of serious Hib infection had fallen from 1:600 to 1:30,000 by 5 years of age. Many other European countries have introduced, or are in the process of introducing, a routine Hib immunisation programme. Because the epidemiology of Haemophilus influenzae infection is changing so dramatically, it is opportune to review Haemophilus influenzae as it was perceived in the pre-vaccine era (the past) and during vaccine implementation (the present), and how its role may change in the post-vaccination era (the future). This review will summarise the historical landmarks that have led to our present-day understanding of Haemophilus influenzae pathogenicity, the concerns about antibiotic resistance, the features of the host immune response to Haemophilus influenzae, and the introduction of the Hib vaccine. Furthermore, the possible importance of this organism in the future will be discussed.

Antibody responses and symptoms after DTP and either tetanus or diphtheria Haemophilus influenzae type B conjugate vaccines given for primary immunisation by separate or mixed injection

The safety and immunogenicity of two conjugate Haemophilus influenzae type B (Hib) vaccines administered either mixed with, or in separate limbs to, a whole-cell DTP vaccine, was compared in infants vaccinated at 2, 3 and 4 months of age. Antibody titres to purified polyribosylribitol phosphate, diphtheria, and to pertussis antigens between infants who received the Hib and DPT vaccines in separate limbs or in the same limbs were similar (P > 0.1) while antibody titres to tetanus toxoid were higher in the later group (P < 0.05). This study demonstrated that both Hib vaccines can be mixed with whole-cell DTP vaccine without reducing immunogenicity of either vaccine or increasing the incidence of adverse reactions.