Acellular-Pertussis, Hepatitis B, Inactivated Polio and Haemo

[Human Vaccines 1:3, 112-117; May/June 2005]; ©2005 Landes Bioscience

Lot-to-Lot Consistency of a Combined Hexavalent Diptheria-TetanusAcellular-Pertussis, Hepatitis B, Inactivated Polio and Haemophilus b Conjugate Vaccine, Administered to Healthy Chilean Infants at Two, Four and Six Months of Age Research Paper

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Objectives: To assess the safety, immunogenicity and lot consistency of a liquid hexavalent combined vaccine (DTaP-IPV-PRP~T-HBs, HEXAVAC®) (Sanofi-Pasteur MSD, France) administered to infants at two, four and six months of age. Methods: A total of 1028 infants were vaccinated with one of three vaccine lots, in a randomized, double-blind fashion. Equivalence testing was used to compare post-vaccination seroprotection/seroconversion rates and geometric mean titers (GMTs) for each antigen between the three lots. Blood samples were drawn before vaccination and one month after the third dose. Local and systemic adverse events were monitored for three days following each injection. Results: Equivalence between lots was demonstrated for all antigens, on post-dose 3 seroprotection/seroconversion rates and GMTs. Reported rates of local and systemic adverse events tended to increase with subsequent doses. Altogether, 11.8% of the infants reported at least one adverse local event (mainly redness and induration/swelling) after the first dose and 36.1% after the third dose. Systemic adverse events (mainly irritability and fever) were reported by 39.2% of the infants after the first dose and by 57.5% after the third one. Conclusion: Three separate lots of the liquid hexavalent combined vaccine induced consistently protective antibody responses against all antigens. These results and the well established clinical tolerability of this combined vaccine make it suitable for primary immunization of infants at two, four and six months of age.

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1Centro para Vacunas en Desarollo; Santiago, Chile

4Sanofi-Pasteur MSD; Lyon, France 5Center

for Vaccine Development; University of Maryland School of Medicine; Baltimore, Maryland USA

Received 01/20/05; Accepted 05/09/05

SC

Previously published online as a Human Vaccines E-publication: http://www.landesbioscience.com/journals/vaccines/abstract.php?id=1848

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*Correspondence to: Rosanna M. Lagos; Centro para Vacunas en Desarrollo-Chile; Hospital de Niños Roberto del Río; Avenida Zañartu 1085 (4º Piso); Independencia, Santiago Chile; Email: [email protected]

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3Merck & Co; West Point, Pennsylvania USA

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2Sanofi-Pasteur; Lyon, France

INTRODUCTION

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KEY WORDS

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ACKNOWLEDGEMENTS

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vaccine, consistency, combined, liquid, hexavalent

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Presented in part at the 37th Annual Meeting of the IDSA, Philadelphia, USA, November 1999, and at the 18th annual meeting of the European Society for Pediatric Infectious Diseases (ESPID), Noordwijk, The Netherlands, 3–5 May 2000.

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ABSTRACT

Rosanna Lagos1,* Agnès Hoffenbach2 Michel Scemama2 Martin Dupuy2 Florian Schodel3 Luc Hessel4 Myron Levine5

The number of injected vaccines recommended for infant immunization has increased over the last 15 years and has increased the demand for new combination vaccines that combine several antigens into a single injection. These combination vaccines are intended to reduce discomfort by decreasing the number of injections, decrease the costs of vaccine delivery, and simplify storage. In doing so, it is expected that combination vaccines will increase compliance with vaccination and ultimately improve vaccine coverage.1-3 The World Health Organization (WHO) and the Global Alliance for Vaccines and Immunization (GAVI) recommend that hepatitis B vaccine be administered to all infants worldwide and that Haemophilus influenzae type b (Hib) conjugate vaccine be used programmatically in countries where a notable disease burden has been demonstrated, or is expected to exist based on regional surveillance data collected in neighboring populations.4,5 Furthermore, the accelerating disappearance of poliomyelitis as an epidemic disease, and the rare but persistent occurrence of cases of paralysis caused by the attenuated oral polio vaccine (OPV) have led to a move towards injectable, inactivated poliovirus vaccine (IPV).6 For example, in the United States of America IPV replaced OPV6,7 in year 2000. Most countries in Western Europe have already switched to IPV or are planning to do so in the near future. After worldwide polio eradication, the option of continuing vaccination with IPV would minimize the risk of emergence of vaccine-derived polioviruses (VDPV), maintain population immunity against polio and thereby deter the use of polioviruses as a biological weapon.7 Combining the IPV vaccine to the vaccines recommended in childhood immunization programmes should facilitate the shift to IPV in countries where polio is eradicated. Human Vaccines

2005; Vol. 1 Issue 3

Lot Consistency of a Combined Hexavalent Vaccine (DTaP-IPV-PRP~T-HBs, HEXAVAC®)

We studied the safety and immunogencity of a liquid hexavalent combination vaccine that contains diphtheria (D), tetanus (T), a two-component (pertussis toxoid [PT] and filamentous haemagglutinin [FHA]) acellular pertussis vaccine (aP), hepatitis B (HB), inactivated poliovirus (IPV) and Haemophilus influenzae type b conjugated to tetanus toxoid (PRP-T) antigens (Hexavac®, Sanofi-Pasteur MSD, Lyon, France), when administered to Chilean infants at 2, 4 and 6 months of age. The immunogenicity and safety of this vaccine was previously assessed in European infants, where it was shown to provide effective protection against the six diseases, and to yield a safety profile similar to the separate administration of the reference, licensed, pentavalent DTaP-IPV/PRP-T vaccine (PENTAVAC™) and hepatitis B vaccine (HB-VAX® II).8 As of January 1, 2005, Hexavac® has been licensed for the primary series and booster dose in children less than two years of age in 49 countries, including Chile.8,9 Earlier experience with DTP-PRP-T or DTaP-IPV/PRP-T showed that Chilean infants had higher local reaction rates and higher antibody responses to PRP than European infants.10 The present study represented the first time that the safety and immunogenicity of the liquid hexavalent combined vaccine was evaluated in a nonEuropean infant population. Three manufacturing lots were used and compared for consistency of immune responses.

MATERIALS AND METHODS

Study population and plan. This double blind, randomized, parallel group study was conducted in five health centres in Santiago, Chile. Before study initiation, the clinical protocol was reviewed and approved by the Ethics Committee of the Servicio de Salud Metropolitano Norte (Santiago, Chile) and by the Institutional Review Board of the University of Maryland in Baltimore (USA). Written informed consent was obtained from at least one parent or legally acceptable representative of each child enrolled in the study. Healthy seven to 11 week-old infants born after 36 weeks of pregnancy with a birth weight >2500 g, were eligible for inclusion in the study. Exclusion criteria were a severe chronic disease, an uncontrolled coagulopathy, a known congenital or acquired immunodeficiency, a history of sudden infant death syndrome in a sibling, a history of seizures, a history of diphtheria, tetanus, pertussis, poliomyelitis, Haemophilus influenzae type b or hepatitis B infection or vaccination, or a known allergy to a vaccine component. Any infant who had received treatment in the previous 4 weeks that was likely to alter the immune response or whose mother was vaccinated with HB vaccine in the previous year was also excluded. Infants were randomly allocated in chronological order of enrolment to receive three doses of one of the three lots of the liquid hexavalent combined vaccine, according to a centralized list. Vaccine. The liquid hexavalent DTaP-IPV-HB-PRP-T combined vaccine was manufactured by Sanofi-Pasteur (formely Aventis Pasteur), Lyon, France. Vaccine was supplied in a prefilled 0.5 mL syringe with a mounted 16-mm (5/8 inch) 25-gauge needle for intramuscular injection. Each 0.5 mL dose of vaccine contained >20 IU purified D toxoid, >40 IU purified T toxoid, 25 µg purified detoxified PT, 25 µg purified FHA, 12 µg purified Hib polysaccharide (polyribosyl ribitol phosphate) conjugated to tetanus toxoid (PRP-T), IPV types 1 (40 D-Ag U), 2 (8 D-Ag U) and 3 (32 D-Ag U) and 5 µg recombinant yeast-derived HB surface antigen. Antigens were adsorbed onto aluminium gel (0.85 mg aluminium), and made up to 0.5 mL with buffered saline solution. The vaccine was preservative-free. Three lots were used in the study, # S3127, S3128 and S3170. Vaccines were administered via deep intramuscular injection into the anterolateral aspect of the right thigh. The vaccination schedule consisted of a primary series of three doses of vaccine administered at two, four and six months of age.

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Safety assessment. Infants remained under medical supervision for 15 minutes after each injection to monitor immediate reactions. Parents were asked to record the rectal temperature of their child each day for the first three days following each injection. They were also asked to report in a diary card any injection-site reaction or systemic adverse experience that occurred during these three days. Injection site reactions included a list of solicited reactions (redness or induration/oedema/swelling >2.0 cm) and any other unsolicited injection site reaction. Systemic adverse events included a list of solicited events (fever, i.e., rectal temperature (38˚C), unusual drowsiness, irritability and/or unusual crying, inconsolable crying persisting for more than three hours, vomiting and/or diarrhoea, insomnia and decreased appetite), and any other unsolicited systemic adverse event (AE). Events that resulted in a physician visit during the month following vaccination and serious adverse events were also reported. The reactogenicity profile was determined by describing the rates of immediate reactions (within 15 min. of the injection), of local and systemic adverse events between 15 min. and three days after injection, of adverse events requiring a medical visit within one month of vaccination and of serious adverse events (SAE) related to the vaccine. Judgments of causal association between administration of the study vaccine and AEs or SAEs were independently made by the responsible investigator and by the appropriate sponsor’s representative, according to standard criteria of the ICH-GCP Guidelines (i.e., temporal association with vaccination; likelihood of other etiologies, etc.). Immunogenicity assessment. All serological analyses were performed at the Sanofi-Pasteur Clinical Immunology Laboratory (Val de Reuil, France) on blinded blood samples collected immediately prior to the first vaccination (two months of age) and four to six weeks after the third injection (seven months of age). Antibody assays were performed blinded, and the two sera from the same child were assayed at the same time. Anti-HB antibody titers were determined by radioimmunoassay (RIA) using AUSAB® test kits from Abbott Laboratories (North Chicago, IL) against a WHO reference preparation.11 The lower limit of detection was 2 mIU/mL. Antibodies against PT and FHA were measured with enzyme-linked immunosorbent assays (ELISA), each with a lower limit of detection of two ELISA units (EU)/mL.12 Diphtheria antitoxin and tetanus antitoxin titers were measured by ELISA13,14 with lower limits of detection of 0.006 IU/mL. Neutralizing antibodies to poliovirus types 1, 2 and 3 were determined by seroneutralisation on HEp-2 cells,15 with a lower limit of detection of five (reciprocal dilution). Anti-PRP antibody response was assessed with a Farr-type RIA16 using 125I-labelled polysaccharide,17 with a minimum limit of detection of 0.07 µg/mL. The immunogenicity endpoints were the seroprotection or seroconversion rates obtained one month after the third vaccine dose, calculated as the percentage of subjects who achieved established seroprotective threshold concentrations of antibodies to diphtheria (0.01 and 0.1 IU/mL),18 tetanus (0.01 and 0.1 IU/mL),19 PRP (0.15 and 1 µg/mL),20 poliovirus types 1, 2 and 3 > 5 reciprocal dilution,21 and HB (10 IU/mL),22 or, for PT and FHA, who displayed at least a four-fold increase in antibody titres from baseline. In addition, the geometric mean titres (GMTs) and their 95% confidence intervals (CI0.95) before and after immunisation were calculated for each vaccine antigen. Statistical analyses. The statistical analysis was done by the SanofiPasteur Biometry Department (Lyon, France) using SAS software (SAS Institute Inc., Cary, NC, USA). The primary objective was to test the lot-to-lot consistency of the three lots on the seroconversion or seroprotection rates, one month after the third dose of the two-four-six month’s vaccination schedule. The maximum clinically acceptable difference in seroprotection or seroconversion rates between two lots was 10% for each antigen. It was concluded that two lots were equivalent if, for each antigen, the limit (absolute value) of the two-sided 90% confidence interval of the observed difference, one month after the third dose, did not exceed 10%. If the condition was satisfied for each pair of lots, it was concluded that the three lots were equivalent for the given antigen. If equivalence was demonstrated for each of the nine antigens, it was concluded that the three lots were globally equivalent. It was calculated that three hundred assessable subjects per group were needed to

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Table 1 Observed seroprotection and seroconversion rates and GMTs* for each component of the combined diphtheria, tetanus, acellular pertussis, inactivated poliomyelitis, Haemophilus influenzae type b and hepatitis B vaccine (Hexavac), one month after the third dose of the vaccine given at 2, 4 and 6 months of age to Chilean infants Seroprotection/seroconversion rate % [95% CI]Post-dose 3 GMT Vaccine

Antigen

Unit

Batch # S3127

Batch # S3128

Batch #

Pooled

S3170

Batches

Batch # S3127

Batch #

Batch #

S3128

S3170

Batches

Pooled

N=

GMT

N= GMT

N= GMT

N= GMT

257

331

838 402

HBs

mIU/mL

96.3 [93.4–98.1]

95.5 [92.4–97.6]

96.5 [93.5–98.4]

96.1 [94.5–97.3]

294

458

287

420

PT

EU/mL

93 [89.4–95.7]

91 [87.0–94.1]

93 [89.0–95.9]

92.3 [90.3–94.1]

299

70.8

289 71.5

255 72.3

843 71.5

FHA FHA

EU/mL

91.3 [87.3–94.3]

90.8 [86.7–93.9]

93.5 [89.7–96.2]

91.8 [89.7–93.6]

299

190

288

257

210

844 192

Tetanus toxoid

IU/mL

100 [98.8–100]

100 [98.7–100]

100 [98.6–100]

100 [98.6–100]

298

6.30

286 6.49

256 6.48

840 6.42

Diphtheria toxoid

IU/mL

100 [98.8–100]

100 [98.7–100]

100 [98.6–100]

100 [99.6–100]

297

1.71

283 1.77

253 1.59

833 1.69

Poliovirus type 1

1/dil.

100 [98.6–100]

100 [98.6–100]

100 [98.5–100]

100 [99.5–100]

269

2459

257 2007

237 1986

763 2149

Poliovirus type 2

1/dil.

100 [98.6–100]

100 [98.6–100]

100 [98.5–100]

100 [99.5–100]

269

1902

257 1574

237 1679

763 1717

Poliovirus type 3

1/dil.

100 [98.6–100]

100 [98.6–100]

100 [98.4–100]

100 [99.5–100]

269

3010

257 2398

236 2239

762 2544

PRP§

µg/mL

97 [94.4–98.6]

98.3 [96.0–99.4]

97.3 [94.4–98.9]

97.5 [96.2–98.5]

300

3.95

289 4.37

256 4.05

845 4.12

178

*Per protocol analysis sample set. § ≥ 0.15 µg/mL.

conclude that the three lots were globally equivalent with an overall alpha risk of 5% and a power of at least 96%. Therefore, a sample size of 365 subjects per group was targeted to offset an expected 18% rate of protocol deviations and missing immunogenicity data. Safety was a secondary, descriptive objective. The rates and 95% CI of immediate reactions; of local and systemic reactions occurred within 72 hours following vaccination; and of any clinical condition that resulted in a medical visit within 30 days after each vaccination were calculate for each vaccine lot. Similarly, all SAE occurred from inclusion until 30 post last dose days were described.

RESULTS Subject population. From June to December 1997, 1028 infants were enrolled in this study and randomized into 3 groups to receive three doses of one of the three batches: S3127 (n = 358), S3128 (n = 359) or S3170 (n = 311). Mean age at enrollment was 62.9 ± 3.7 days, and 50.5% were boys. Fifty-nine infants did not complete the study. Four infants died of a Sudden Infant Death Syndrome (SIDS) that occurred 16, 23, or 47 days after the first dose and 8 days after the second dose, respectively. None of these SIDS was considered related to vaccination. Thirty-two infants were withdrawn from the study by their parents. Eighteen infants were discontinued by the investigator for medical reasons unrelated to vaccination (n = 10) and 5 infants for medical reasons related to vaccination, such as fever higher than 40˚C (n = 1), skin rashes (n = 3) and hypotonic hyporesponsiveness-like episode (n = 1). Finally, a total of 969 (94.3%) infants completed the primary series. Immunogenicity. Seroprotection/seroconversion rates and GMTs measured in each group are shown for each antigen in Table 1. The lot-to-lot consistency was demonstrated for all antigens, as the equivalence was statistically demonstrated for each pair of lots, in terms of sero-protection/ seroconversion rates and GMTs, one month after the third dose.

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For each pair of lots, the per protocol analysis showed a maximum (upper or lower bound of the 90% confidence interval) ratio for the GMT of 1.32, 1.74, 1.24, 0.89, 1.44, 1.40, 1.57, 0.91 and 0.78 for anti-PRP, anti-HBs, anti-diphtheria, anti-tetanus, anti-polio type 1, 2 and 3, anti-PT and anti-FHA antibodies, respectively. The maximum (upper or lower bound of the 90% confidence interval) differences in the seroprotection/seroconversion rates to PRP, HBs, D, T, any type of poliovirus, PT and FHA were 3.54, 3.90, 0.95, 1.05, 1.13, 5.93 and 6.66 %, respectively. Safety profile. No immediate adverse reaction was observed. The proportion of infants with at least one local adverse reaction during the first three days after injection was approximately 12% after the first dose, increasing to 28% and 36% after dose 2 and 3 (Table 2). The solicited adverse reactions, redness and induration/oedema/swelling, were the most frequently reported. The majority of local reactions (84% of redness and 93% of induration/oedema/swelling) measured 7 cm), both appearing on the day of the second injection: redness of the entire thigh (n = 1) and swelling of the entire thigh (n = 1). Both reactions resolved within two days. Solicited and unsolicited local reactions were evenly distributed across the three study groups (not shown). The proportion of infants with at least one solicited systemic adverse event during the three days after an injection increased from 39% after dose 1 to 56% and 58% after dose 2 and dose 3, respectively (Table 2). Almost all the events (96.1%) were deemed related to vaccination. Irritability and/or unusual crying were the most frequently reported systemic adverse event. The majority (88%) of the reported febrile episodes were mild (38–38.9˚C, rectal). High fever (≥40.0˚C) was reported on four occasions and was deemed related to vaccination in three cases. In all cases, high fever episodes started on the day of injection, lasted four to five days and were

Human Vaccines



Proportion of Chilean infants experiencing local and systemic adverse events within 72 hours of immunisation with the hexavalent combined diphtheria, tetanus, acellular pertussis, inactivated poliomyelitis, Haemophilus influenzae type b and hepatitis B vaccine (Hexavac?) at 2, 4 and 6 months of age.

The study reported herein was primarily designed to assess the consistency of the immune response elicited by three manufacturing lots of the liquid hexavalent combination vaccine in Chilean infants. The statistical analysis of the immune responses recorded following N subjects= 1026 993 978 vaccination with the three lots con2 nd dose 3 rd dose 1 st dose firmed the lot-to-lot consistency of the vaccine and showed that, in Chilean Any local reaction 11.8 27.5 36.1 infants, the three-dose primary series was skin redness (>2 cm) 2.4 10.2 17.4 highly immunogenic for all antigens. 0.9 2.3 1.4 skin redness (>5 cm) The seroprotection rates to HBs skin induration/oedema/swelling (≥ 2 cm) 9.4 17.7 23.8 antigen measured in the present study, skin induration/oedema/swelling (5 cm) 0.1 2.2 1.3 which were above 95% for all three vacother local reactions † 2.3 10.5 13.2 cine lots, are consistent with responses of Any systemic AEs 39.2 56.4 57.5 French infants to three doses of the same fever 38.0°C or > 12.1 26.8 27.2 vaccine.8 Similarly, seroconversion rates fever > 38.0 < 38.9°C 11.3 23.9 22.9 for PT and FHA did not differ from those previously reported with less 0.7 2.8 4.1 fever > 39.0 < 39.9°C complex combination vaccines containing fever > 40.0°C 0.1 0.1 0.2 the same acellular pertussis vaccine27 drowsiness 8.2 3.5 3.2 and compared well to those measured in irritability/unusual crying 17.7 35 40.7 Swedish infants with the pentavalent inconsolable crying >3 h 0 0 0 [DTaP-IPV/PRP-T] vaccine,28 and in vomiting/diarrhoea 1.9 1.9 3.4 French infants with the present liquid insomnia 0.4 0.1 0.3 hexavalent vaccine.8 Even though there is no established immunologic correlate loss of appetite 0.5 0.2 0.8 ‡ of protection for acellular pertussis 10.7 14.8 11.2 other systemic AE vaccines,29 it may be inferred from *At least one reaction to any of the three primary doses. †Other local reactions: injection site pain, injection site inflammation. ‡Other systemic adverse recent epidemiological data collected in events: minor childhood illnesses (e.g., respiratory, skin, or gastrointestinal disorders). Sweden, where a pentavalent vaccine containing the same acellular pertussis associated with other events. The incidence of fever was higher after the components as in the present hexavalent vaccine is used30 that antisecond and third doses than after the first one. Thirty-one nonsolicited body titers to pertussis antigens measured in the present study systemic adverse events were reported as related to vaccination. These causal- should confer protection. For tetanus and diphtheria, the seroproity judgments were based either on temporal association with vaccination, tection rates and GMTs were of the same magnitude as those unspecific nature of the symptoms, and/ or lack of demonstration of other described elsewhere with this hexavalent vaccine, or with combinaetiologies. They consisted mainly of respiratory system disorders (n = 10) tions containing fewer antigens.8,10,27 and skin disorders (n = 16). Other cases were malaise (n = 1), cyanosis GMTs of anti-PRP antibodies were lower than those observed in during sleep (n = 1), asthenia (n = 1), colitis (n = 1) and a hypotonic a study on interactions between DTaP, IPV and Act-HIB® vaccines hyporesponsiveness-like episode (n = 1) which started the day after the first 27 injection and lasted three days. This case did not meet the international in Chilean infants; however, more than 97% of the infants reached definition of hypotonic hyporesponsiveness episode. Again, the reports seroprotective levels of anti-PRP antibodies (>0.15 µg/mL). This of solicited and unsolicited systemic adverse events were balanced across seroprotection rate after three doses of PRP-T is as high as those study groups. previously reported in Chilean infants,31,32 and the GMTs were From day 4 to day 30 after vaccination, three (0.3%) out of 1144 events greater than the ones measured with the same vaccine in French were deemed possibly related to vaccination: a bronchitis (that was diagnosed infants.8 The markedly greater immune response to PRP-T in 5 days after the first injection), an otitis media (11 days after the first injecChilean infants versus North American or European infants has tion), and an episode of diarrhoea (11 days after the third injection). been observed consistently.10,27,31-33 In early studies, 25% of Chilean infants reached a concentration >1.0 mcg of PRP antibody DISCUSSION per ml of serum after the first primary dose of vaccine.31-33 A The formulation of combination vaccines is much more complex case/control study undertaken to try and identify factors associated than the simple mixing of antigens.23 Because it is difficult to predict with this robust serologic responses revealed that infants who the physical compatibility and stability of antigens in combinations, mounted such enhanced responses came from significantly lower the clinical evaluation of the immunogenicity and safety of a new than the other infants, and their combined vaccine is necessary to determine the potential modifica- socioeconomic level households 33 had less education. parents tions of the efficacy of antigens. Moreover, demonstration of The response to poliovirus vaccines was at least of the magnitude lot-to-lot consistency of the immune responses to all antigens is a critical step in the development of complex mutivalent vaccines,24,25 previously measured in Chilean infants, either with attenuated oral and has been proposed as a method to validate routine batch release or enhanced-inactivated polio vaccines.27 The introduction of IPV vaccine in national immunization schedules is not currently under testing.26 Table 2


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consideration for Chile, although Latin America was declared polio-free by WHO. The outbreaks of flaccid paralysis due to circulating VDPV during 2000 and 2001 in the Dominican Republic and Haiti34 and during 2001 and 2002 in the Philippines and Madagascar35 underscore the need to ensure high levels of vaccine coverage against polioviruses in countries where attenuated vaccine-derived poliovirus may circulate. The implications of circulating VDPVs have been debated and most experts agree upon the desirability of replacing OPV with IPV in the post-certification era. The introduction of IPV vaccination would have the major advantage of maintaining protection against poliovirus including the circulating VDPVs, for the foreseeable future.7 The different rates of local reactions reported in Chilean and Belgian infants in a clinical trial using the same lot of vaccine and immunization schedule10 highlight the difficulty of obtaining standardized surveillance of safety in different populations, even when the same vaccines are tested using a common protocol. We believe that such differences derive from cultural perceptions and intensity of surveillance for vaccine reactions across study sites, rather than to a real increased propensity of Chilean infants to manifest higher reactogenicity to vaccinations. In fact, different rates of local or systemic adverse events were also reported in the large-scale efficacy trials carried out with acellular pertussis vaccines, where the safety profile was strongly dependent on the studied population.36-39 On the other hand, the reactogenicity observed in this study is consistent with that experienced by Chilean infants who received the pentavalent, DTaP-IPV/PRP-T vaccine (PENTAVAC®), in a previously reported study.22 The present study showed some higher rates of local and systemic events with subsequent doses. Such a trend was not observed in French and German infants,8,40 but was previously reported in Chilean infants for the local reactions to a DT-acellular pertussis vaccine combined or concurrently administered with PRP-T.22 Nevertheless, the rates of fever >38˚C, of local reaction, and of solicited systemic adverse events, such as irritability/crying and vomiting/diarrhoea were definitively much lower (three to four times lower) than those reported with a DT whole-cell pertussis vaccine reconstituted with PRP-T in Chilean infants.10 In summary, this study showed that the liquid hexavalent combined vaccine induced satisfactory immune responses to all antigens, yielding seroprotection rates greater than 95% for HB and Hib and equal to 100% for D, T and the three types of polio viruses. The effective antibody response to HB, both in terms of GMT and seroprotection rates, may indicate that the liquid hexavalent combined vaccine could be included in the national immunization schedule of countries where the endemicity of hepatitis B is low. Similarly the effective responses to PRP and polio vaccines pave the path for a future shift to IPV and/or wide scale use of Hib vaccination. This study did not assess the immune response or the safety of the combination vaccine in infants who had received a dose of hepatitis B vaccine at birth. Notably, the robust collective immune response documented was associated with a satisfactory safety profile, similar to that reported with a pentavalent [DTaP-IPV/PRP-T] vaccine and much better than the one reported with a DTP (whole cell) vaccine in Chilean infants.10,27 Understandably, the price of one dose of liquid hexavalent vaccine is substantially higher than the cumulative costs of the monovalent vaccine components, or of other less complex combinations containing fewer vaccine antigens. Nonetheless, as combination vaccines are becoming a compelling necessity rather than a desirable option, 116

public and private vaccine purchasers will need to pay careful consideration to the nonvaccine costs of the immunization programs, at the moment of evaluating the cost-benefit of various available combinations. The liquid hexavalent vaccine discussed here could contribute to reduce the cost of the immunization programs by facilitating the storage, distribution and administration of the vaccines, and could increase their benefits by improving acceptance of vaccination by parents and health care providers, and by increasing vaccine coverage rates for under utilized vaccine antigens such as HB and PRP conjugate. We believe that this combination vaccine is a valid alternative in developed countries that are already using DTaP and IPV vaccines, as well as in Polio-free middle-income countries that might be considering the implementation of such vaccines in their routine infants’ immunization programs. References 1. Di Fabio JL, de Quadros C. Considerations for combination vaccine development and use in the developing world. Clin Infect Dis 2001; 33:S340-5. 2. Pichichero ME. New combination vaccines. Pediatr Clin North Am 2000; 47:407-26. 3. Hinman AR. Perspectives on the state of combination vaccines: Summary of the rapporteur for the International Symposium on Combination Vaccines. Clin Infect Dis 2001; 33:S372-5. 4. Martin JF, Marshall J. New tendencies and strategies in international immunisation: GAVI and The Vaccine Fund. Vaccine 2003; 21:587-92. 5. Lagos R, Levine OS, Avendano A, Horwitz I, Levine MM. The introduction of routine Haemophilus influenzae type b conjugate vaccine in Chile: A framework for evaluating new vaccines in newly industrializing countries. Pediatr Infect Dis J 1998; 1):S139-48. 6. American Academy of Pediatrics Committee on Infectious Diseases. Poliomyelitis prevention: Recommendations for use of inactivated poliovirus vaccine and live oral poliovirus vaccine. Pediatrics 1997; 99:300-5. 7. Technical Consultative Group to the World Health Organization on the Global Eradication of Poliomyelitis. “Endgame” issues for the global polio eradication initiative. Clin Infect Dis 2002; 34:72-7. 8. Mallet E, Fabre P, Pines E, Salomon H, Staub T, Schödel F, Mendelman P, Hessel L, Chryssomalis G, Vidor E, Hoffenbach A. And the hexavalent Vaccine Trial Study Group. Immunogenicity and safety of a new liquid hexavalent combined vaccine compared with separate administration of reference licensed vaccines in infants. Hexavalent Vaccine Trial Study Group. Pediatr Infect Dis J 2000; 19:1119-27. 9. Mallet E, Belohradsky BH, Lagos R, Gothefors L, Camier P, Carrière JP, Kanra G, Hoffenbach H, Langue J, Undreiner F, Roussel F, Reinert P, Flormark CE, Stojanov S, Liese J, Levine MM, Muñoz A, Schödel F, Hessel LL. A liquid hexavalent combined vaccine against diphtheria, tetanus, pertussis, poliomyelitis, Haemophilus influenzae type B and hepatitis B: Review of immunogenicity and safety. 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