Antipolyribosyl ribitol phosphate response of premature infants to primary and booster vaccination with a combined diphtheria-tetanus-acellular pertussis-hepatitis B-inactivated polio virus/Haemophilus influenzae type b vaccine

A worldwide overview for hexavalent vaccines and a glimpse into Turkiye's perspective

The surge in recommended vaccinations for child's has spurred the development of combination vaccines, notably hexavalent vaccines, which provide multiple immunizations in a single dose. These vaccines offer various advantages, such as streamlining vaccination schedules, minimizing injection-related pain and exposure to preservatives, expanding vaccine coverage, and reducing administration costs. However, the intricate and expensive development of these vaccines presents substantial challenges, requiring increased investment and healthcare provider education to optimize their utilization and sustain high vaccination rates. Turkey, known for its robust vaccine coverage, strategic geographic location, and the influx of refugees, is at a critical juncture for integrating hexavalent vaccines into national programs. This transition is especially relevant given the rising vaccine hesitancy and the potential resurgence of vaccine-preventable diseases. This review assesses the deployment of hexavalent vaccines, examining their benefits and challenges through clinical trials and global experiences, with a specific emphasis on Turkiye's public health context.

Severe pertussis disease in a paediatric population: The role of age, vaccination status and prematurity

AIM

To estimate hospitalisation rate and investigate the role of age, prematurity and vaccination status in severe pertussis cases.

METHODS

We retrospectively evaluated 200 children aged 0-14 years, admitted to the emergency rooms of Meyer Hospital of Florence and Pisa Hospital with a diagnosis of pertussis from 1 October 2010 to 31 January 2020.

RESULTS

Children younger than 12 months were 63.0%. Preterm infants were 6.5%. The rate of hospitalisation was 49.0%. Among hospitalised cases, 80.6% were younger than 5 months. Overall, 62.0% were unvaccinated; this percentage increased among hospitalised (73.5%) and preterm subsamples (76.9%). Delays in pertussis vaccination were found in 57.7% of term infants and in 80.0% of preterms. Multivariable analysis confirmed the age under 2 months as the variable at higher risk for hospitalisation (OR 4.49, 95% CI 1.85-10.96, p < 0.001). Being fully vaccinated represented a significant protective factor (OR 0.12, 95% CI 0.04-0.35, p < 0.001).

CONCLUSION

Older classes of age and a complete vaccination, in time with the recommended schedule, are both protective factors for hospitalisation in severe pertussis disease. The widespread vaccination delay frequently observed in preterm children may be the cause for their higher rate of hospitalisation.

Factors affecting antibody responses to immunizations in infants born to women immunized against pertussis in pregnancy and unimmunized women: Individual-Participant Data Meta-analysis

BACKGROUND

Exploring factors that affect immune responses to immunizations in infants born to women immunized with tetanus-diphtheria-acellular-pertussis (Tdap) in pregnancy compared with unimmunized women is important in designing immunization programs.

METHODS

Individual-participant data meta-analysis of 8 studies reporting post-immunization immunoglobulin G (IgG) levels to vaccine antigens in infants born to either women immunized with Tdap in pregnancy or unimmunized women, using mixed-effects models.

RESULTS

In infants of Tdap-immunized women, two-fold higher levels of anti-pertussis toxin (PT) and anti-diphtheria-toxoid (DT) IgG pre-primary immunization were associated with 9% and 10% lower post-primary immunization levels, (geometric mean ratio [GMR], PT: 0.91; 95% CI, 0.88-0.95,n = 494, DT: 0.9; 0.87-0.93,n = 519). Timing of immunization in pregnancy did not affect post-primary immunization anti-Bordetella pertussis, anti-tetanus-toxoid (TT) and anti-DT IgG levels. Spacing of infant immunization did not affect post-primary immunization anti-B. pertussis and anti-DT levels. In infants of Tdap-immunized women, two-fold higher levels of anti-PT and anti-filamentous haemagglutinin (FHA) IgG pre-primary immunization were associated with lower post-booster immunization levels, (GMR, PT: 0.91; 0.85-0.97,n = 224, FHA: 0.92; 0.85-0.99,n = 232). Timing of immunization in pregnancy did not affect post-booster immunization anti-Bordetella pertussis, anti-tetanus-toxoid (TT) and anti-DT IgG levels. Spacing of infant immunization did not affect post-booster immunization anti-PT, anti-pertactin (PRN), anti-TT and anti-DT IgG levels. In infants of unimmunized women, two-fold higher IgG levels of some vaccine antigens pre-primary immunization were associated with 8-17% lower post-primary immunization levels (GMR, PT 0.92, 95% CI:0.88-0.97, n = 373; FHA:0.88, 95% CI:0.85-0.92,n = 378; PRN:0.84, 95% CI:0.81-0.88, n = 367; TT:0.88, 95% CI:0.83-0.93, n = 241; DT: 0.83, 95% CI:0.79-0.87,n = 278). Two-fold higher levels of anti-FHA IgG pre-primary immunization were associated with 8% lower post-booster immunization levels (GMR, 0.92; 95% CI: 0.86-0.99,n = 138).

DISCUSSION

Increased IgG levels pre-primary immunization is associated with reduced post-primary and post-booster immunization levels for some antigens in infants of women immunized or unimmunized in pregnancy, but their clinical significance is uncertain.

Factors That Influence Infant Immunity and Vaccine Responses

The neonatal period and early infancy are times of increased vulnerability to infection. The immune system of infants undergoes rapid changes and a number of factors can influence the maturation and function of the early infant immune system, amongst these factors are maternal infections and immunity. Infants who are HIV-exposed, but uninfected show important immune alterations, which are likely to be associated with the increased morbidity and mortality observed in these infants. Maternally derived antibodies are crucial in early life to protect infants from infection during the time when their own immune system is becoming more experienced and fully mature. However, maternal antibodies can also interfere with the infant's own antibody responses to primary vaccination. Preterm infants are particularly vulnerable to infection, having not had the opportunity to benefit from the transplacental transfer of maternal antibodies in late pregnancy. In addition, further differences have been observed in the innate and adaptive immune system between preterm and term infants. Here, we focus on maternal influences on the infant immune system, using HIV and maternal vaccination as examples and finish by considering how prematurity impacts infant immune responses to vaccination.

Invasive Haemophilus influenzae Type b Disease in the Post Hexavalent Era: Ten Years of Molecular Surveillance in Tuscany

BACKGROUND

The epidemiologic characteristics of invasive Haemophilus influenzae type b disease (HIBD) have markedly changed since the introduction of the Haemophilus influenzae type b (Hib) conjugate vaccine worldwide. The immunization schedule against Haemophilus influenzae type b differs in Europe.

METHODS

This is a retrospective observational study which evaluates all the data included in the molecular surveillance register for invasive infectious diseases at the Laboratory of Molecular Diagnosis at Meyer Children's University Hospital from December 2008 to December 2018 with a diagnosis of invasive HIBD in children <5 years of age.

RESULTS

We identified 4 cases of HIBD: all the cases presented signs or symptoms of invasive infection and the H. influenzae type b was identified in cerebrospinal fluid, or blood or bronchoalveolar lavage by molecular test. The crude incidence for Hib invasive disease in Tuscany is 0.26/100,000 p-y in children younger than 5 years, significantly different from the incidence rate before the introduction of the Hib vaccination. Vaccination effectiveness can be estimated at 97.9% and the impact of hexavalent (2p+1) vaccine at 99.6%.

CONCLUSIONS

This work confirms the high impact of the hexavalent vaccine 2p+1 schedule for HIBD in children <5 years, emphasizing the role of molecular test for HIBD diagnosis and surveillance.

Biological sex influences antibody responses to routine vaccinations in the first year of life

AIM

We investigated the effect of early-life factors, namely sex, delivery mode, feeding method and antibiotic exposure, on antibody responses to routine vaccinations administered during the first year of life.

METHODS

One and seven months after the primary course of routine vaccines and 1 month after routine vaccines at 12 months of age, antibodies against 26 vaccine antigens were measured in 398 healthy infants. The geometric mean concentration (GMC) of antibodies (adjusted for effect modifiers with multiple linear regression) and the seroprotection rate for each vaccine were compared for each early-life factor.

RESULTS

Sex had an influence on GMCs. Antibody concentrations were significantly lower at 7 months of age in females for tetanus and filamentous haemagglutinin and at 13 months of age for pertactin. In contrast, at 13 months of age, antibody concentrations were significantly higher in females for polio type 3, pneumococcal serotype 6A and measles. Sex did not have an influence on seroprotection rates. Delivery mode, feeding method and antibiotic exposure did not exert a substantial influence on vaccine antibody concentrations.

CONCLUSION

There is a difference between males and females in the humoral response to routine vaccinations in the first year of life.

Hexavalent vaccines in preterm infants: an update by Italian Society of Pediatric Allergy and Immunology jointly with the Italian Society of Neonatology

Hexavalent vaccines, protecting against six diseases (diphtheria, tetanus, pertussis [DTaP], poliovirus, hepatitis B virus [HBV], and Haemophilus influenzae type b [Hib], are routinely the standard of care in Europe. The use of combined vaccines allows the reduction of number of injections and side effects, the reduction of costs, and the increase in adherence of the family to the vaccination schedule both in terms of the number of doses and timing. The safety profile, efficacy and effectiveness of hexavalent vaccines have been extensively documented in infants and children born at term, and data are accumulating in preterm infants. Hexavalent vaccines are particularly important for preterm infants, who are at increased risk for severe forms of vaccine preventable diseases. However, immunization delay has been commonly reported in this age group. All the three hexavalent vaccines currently marketed in Italy can be used in preterm infants, and recent data confirm that hexavalent vaccines have a similar or lower incidence of adverse events in preterm compared to full-term infants; this is likely due to a weaker immune system response and reduced ability to induce an inflammatory response in preterm infants. Apnoea episodes are the adverse events that can occur in the most severe preterm infants and / or with history of respiratory distress. The risk of apnoea after vaccination seems to be related to a lower gestational age and a lower birth weight, supporting the hypothesis that it represents an unspecific response of the preterm infant to different procedures. High seroprotection rates have been reported in preterm infants vaccinated with hexavalent vaccine. However, a lower gestational age seems to be associated with lower antibody titres against some vaccine antigens (e.g. HBV, Hib, poliovirus serotype 1, and pertussis), regardless of the type of hexavalent vaccine used. Waiting for large effectiveness studies, hexavalent vaccines should be administered in preterm infants according to the same schedule recommended for infants born at term, considering their chronological age and providing an adequate monitoring for cardio-respiratory events in the 48–72 h after vaccination, especially for infants at risk of recurrence of apnoea.

Factors That Influence the Immune Response to Vaccination

There is substantial variation between individuals in the immune response to vaccination. In this review, we provide an overview of the plethora of studies that have investigated factors that influence humoral and cellular vaccine responses in humans. These include intrinsic host factors (such as age, sex, genetics, and comorbidities), perinatal factors (such as gestational age, birth weight, feeding method, and maternal factors), and extrinsic factors (such as preexisting immunity, microbiota, infections, and antibiotics). Further, environmental factors (such as geographic location, season, family size, and toxins), behavioral factors (such as smoking, alcohol consumption, exercise, and sleep), and nutritional factors (such as body mass index, micronutrients, and enteropathy) also influence how individuals respond to vaccines. Moreover, vaccine factors (such as vaccine type, product, adjuvant, and dose) and administration factors (schedule, site, route, time of vaccination, and coadministered vaccines and other drugs) are also important. An understanding of all these factors and their impacts in the design of vaccine studies and decisions on vaccination schedules offers ways to improve vaccine immunogenicity and efficacy.

Immunization of preterm infants with GSK's hexavalent combined diphtheria-tetanus-acellular pertussis-hepatitis B-inactivated poliovirus-Haemophilus influenzae type b conjugate vaccine: A review of safety and immunogenicity

BACKGROUND

Infants with history of prematurity (<37 weeks gestation) and low birth weight (LBW, <2500 g) are at high risk of infection due to functional immaturity of normal physical and immunological defense mechanisms. Despite current recommendations that infants with history of prematurity/LBW should receive routine immunization according to the same schedule and chronological age as full-term infants, immunization is often delayed.

METHODS

Here we summarize 10 clinical studies and 15 years of post-marketing safety surveillance of GSK's hexavalent vaccine (DTPa-HBV-IPV/Hib), a combined diphtheria-tetanus-acellular-pertussis-hepatitis-B-inactivated-poliovirus-Haemophilus influenzae-type-b (Hib) conjugate vaccine, when administered alone, or co-administered with pneumococcal conjugate, rotavirus, and meningococcal vaccines and respiratory syncytial virus IgG to infants with history of prematurity/LBW in clinical trials.

RESULTS

At least 92.5% of infants with history of prematurity/LBW as young as 24 weeks gestation in clinical studies were seropositive to all vaccine antigens after 3-dose primary vaccination with GSK's hexavalent DTPa-HBV-IPV/Hib vaccine, with robust immune responses to booster vaccination. Seropositivity rates and antibody concentrations to hepatitis B and Hib appeared lower in infants with history of prematurity/LBW than term infants. Between 13-30% of medically stable infants with history of prematurity developed apnea after vaccination with GSK's hexavalent DTPa-HBV-IPV/Hib vaccine; usually after dose 1. The occurrence of post-immunization cardiorespiratory events appears to be influenced by the severity of any underlying neonatal condition. Most cardiorespiratory events resolve spontaneously or require minimal intervention. GSK's hexavalent DTPa-HBV-IPV/Hib vaccine was well tolerated in co-administration regimens.

CONCLUSION

GSK's hexavalent DTPa-HBV-IPV/Hib vaccine alone or co-administered with other pediatric vaccines has a clinically acceptable safety and immunogenicity profile when used in infants with history of prematurity/LBW for primary and booster vaccination. Additional studies are needed in very premature and very LBW infants. However, currently available data support using GSK's hexavalent DTPa-HBV-IPV/Hib vaccine to immunize infants with history of prematurity/LBW according to chronological age.

New perspectives for hexavalent vaccines

With the increase in the number of routine vaccinations the development of pentavalent and hexavalent combination vaccines fitting the routine vaccination schedules became a necessity. In this respect, Europe has taken the lead in comparison with other world regions, and routine vaccination with pentavalent and hexavalent combinations including DTPa, Hib, HepB and IPV has been on European vaccination programs for >15years. Since the marketing authorization of Hexavac® and Infanrix Hexa® in 2000, immunization schedules in most European countries have included hexavalent vaccines. In the last years, two new hexavalent vaccines have been licensed and commercialized worldwide. This paper presents a review of the pharmaceutical profiles of the three hexavalent vaccines currently available. In addition, we aim to review safety, co-administration, tolerability and other practical concerns of their use.

Combined hexavalent diphtheria-tetanus-acellular pertussis-hepatitis B-inactivated poliovirus-Haemophilus influenzae type B vaccine; Infanrix™ hexa: twelve years of experience in Italy

Infant vaccination using 2-dose priming at 3 and 5 mo of age with a booster at 11–12 mo of age was pioneered in Italy. The 3-5-11 schedule is now used in a growing number of European countries. Infanrix™ hexa (DTPa-HBV-IPV/Hib, GlaxoSmithKline Vaccines) was first licensed for use in 2000 and has been the only pediatric hexavalent vaccine available since 2005. We reviewed available clinical trial data describing the immunogenicity of DTPa-HBV-IPV/Hib when administered at 3, 5, and 11 mo of age, and conducted an analysis of safety using global and Italian post-marketing surveillance data. In Italy, DTPa-HBV-IPV/Hib has a demonstrated safety record extending over a decade of use, it has been associated with record levels of vaccine coverage, and with sustained disease control in vaccinated cohorts. Hexavalent vaccines will continue to contribute to high vaccine coverage in Italy and across Europe.

DTPa-HBV-IPV/Hib vaccine (Infanrix hexa™): a guide to its use in infants

Infanrix hexa™, a diphtheria, tetanus, acellular pertussis, hepatitis B, inactivated poliomyelitis, and Haemophilus influenzae type b (Hib) conjugate vaccine, is indicated for primary and booster vaccination of infants. Available clinical data from more than a decade of experience with the vaccine indicate that primary and booster vaccination with Infanrix hexa™ is a safe and useful option for providing protection against the common childhood diseases of diphtheria, tetanus, poliomyelitis, pertussis, hepatitis B, and disease caused by Hib.

Combined Haemophilus Influenzae type B-Neisseria meningitidis serogroup C vaccine is immunogenic and well tolerated in preterm infants when coadministered with other routinely recommended vaccines

BACKGROUND

Preterm infants are at greater risk of morbidity from vaccine-preventable diseases. Therefore, their responses to vaccination are of particular interest.

METHODS

In this open, controlled, Spanish multicenter study, we assessed immunogenicity and safety following primary vaccination of 163 preterm infants (n = 56, <31 weeks' gestation; n = 107, 31-36 weeks' gestation) and 150 full-term infants (>36 weeks' gestation), with Haemophilus Influenzae type B (Hib)-MenC-TT, DTaP(diphtheria-tetanus-acellular pertussis vaccine)-HepB-IPV, and PCV7 at 2 to 4-6 months of age followed by booster vaccination at 16 to 18 months of age. Serum bactericidal activity (rabbit complement) against MenC, and antibodies to Hib and hepatitis b (anti-HBs) were determined. Local/general symptoms were assessed after each vaccination via diary cards. Serious adverse events were recorded throughout the study.

RESULTS

There were no statistically significant differences between preterm and full-term infants in either Hib or MenC seroprotection rates or geometric mean concentrations at 1 month postdose 3, before or 1 month postbooster. Postdose 3, >99% of participants had seroprotective anti-HBs antibody concentrations. Anti-HBs geometric mean concentrations was significantly lower in the <31-week group compared with other groups and this difference persisted until 16 to 18 months of age. Hib-MenC-TT vaccine was well tolerated at all ages. There was one death caused by meningococcal serogroup-B sepsis (full term). No serious adverse events were assessed by the investigator as being vaccine related.

CONCLUSIONS

Hib-MenC-TT vaccine had a similar immunogenicity and safety profile in preterm and full-term infants. These results demonstrate that preterm infants can be safely vaccinated with Hib-MenC-TT at the recommended chronologic age without impacting the responses to the Hib and MenC antigens.

Hepatitis B response of premature infants after primary and booster immunisation with a diphtheria-tetanus-acellular pertussis-hepatitis B-inactivated poliovirus/haemophilus influenzae type B vaccine

A range of schedules are recommended for hepatitis B vaccination of premature infants. This open-label study (217744/083) compared the immune response of premature (N = 94) and full-term infants (N = 92) to hepatitis B antigen following primary administration of hexavalent DTPa-HBV-IPV/Hib vaccine at 2–4–6 months and a booster dose at 18 months. Anti-HBsAg antibodies were determined before and one month after primary and booster doses. There were no significant differences in postprimary seroprotection rates (anti-HBsAg >10 mIU/mL; preterm 93.4%; full-term 95.2%) or geometric mean concentrations (634 versus 867 mIU/ml), and neither appeared to be related to gestational length or birth weight. Prebooster seroprotection rates were 75 and 80.6%, respectively. Six premature infants did not respond to primary and booster doses. Primary and booster vaccinations with DTPa-HBV-IPV/Hib elicit satisfactory anti-HBsAg responses in preterm infants, which are not influenced by gestational age or birth weight. This schedule and vaccine will greatly facilitate the immunisation of premature infants.

Review of 8 years of experience with Infanrix hexa (DTPa-HBV-IPV/Hib hexavalent vaccine)

Combination vaccines that include multiple antigens within one formulation are now widely accepted as an effective means of eliciting protection against several diseases at the same time. Owing to improvements in quality and convenient modes of administration, they have become part of routine pediatric practice. Hexavalent vaccines, including diphtheria, tetanus, pertussis, hepatitis B, polio and Haemophilus influenzae type b antigens represent the latest advance in the development of combination vaccines. Over 8 years since its first licensure, this review looks at the immunogenicity, efficacy and safety profile of the only hexavalent pediatric vaccine currently in use--Infanrix hexa (diphtheria, tetanus, acellular pertusis-hepatitis B virus-inactivated poliovirus vaccine/Haemophilus influenzae type b vaccine [DTPa-HBV-IPV/Hib]; GlaxoSmithKline Biologicals, Rixensart, Belgium)--through published clinical trials and postmarketing surveillance data. These data show DTPa-HBV-IPV/Hib to be highly immunogenic and well tolerated across a range of different primary and booster vaccination schedules, as well as when administered concomitantly with other licensed vaccines (e.g., pneumococcal conjugate vaccine). Additional issues surrounding the use of hexavalent vaccines are also reviewed.

Immunogenicity and reactogenicity of DTPa-HBV-IPV/Hib vaccine as primary and booster vaccination in low-birth-weight premature infants

AIM

To assess suitability of a combined DTPa-HBV-IPV/Hib vaccine (Infanrix hexa) for immunization of low-birth-weight (<2.0 kg) preterm infants, with particular focus on the hepatitis B response.

METHODS

Open-label study in 170 preterm infants receiving primary vaccination at 2, 4 and 6 months of age and booster vaccination at 18-24 months. Enrollment and analysis were stratified in two groups: infants with birth weight between 1.5 kg and 2.0 kg (low birth weight: LBW), infants with BW <1.5 kg (very low birth weight: VLBW).

RESULTS

One month after the three dose primary vaccination, 93.7% and 94.9% of infants in VLBW and LBW groups, respectively, had anti-HBs antibody concentrations > or = 10 mIU/mL. High seroprotection and response rates (92.4-100%) to all vaccine antigens were observed. Those were reinforced (>98%) by booster vaccination for all antigens except for HBs in VLBW children: only 88.7% of those had anti-HBs antibody concentrations > or = 10 mIU/mL, compared with 96.5% of LBW children (difference statistically not significant). The vaccine was well tolerated in both groups of infants.

CONCLUSION

Preterm infants will benefit by the administration of a primary and booster vaccination with DTPa-HBV-IPV/Hib vaccine.

Immunogenicity and reactogenicity of a booster dose of a novel combined Haemophilus influenzae type b-Neisseria meningitidis serogroup C-tetanus toxoid conjugate vaccine given to toddlers of 13-14 months of age with antibody persistence up to 31 months of age

BACKGROUND

A combined Haemophilus influenzae type b and Neisseria meningitidis serogroup C tetanus toxoid conjugate vaccine (Hib-MenC-TT) may be a convenient alternative to separate Hib and MenC conjugate vaccines.

METHODS

Healthy infants randomized in a previous study for priming at 2, 4, and 6 months: Hib-MenC-TT primed group, 3 doses of Hib-MenC-TT + DTPa-HBV-IPV (N = 87); MenC-TT primed group, 2 doses of MenC-TT (NeisVac-C; Baxter Healthcare SA, Zuürich, Switzerland) + 3 doses of DTPa/Hib containing vaccines (N = 178); MenC-CRM primed group, 3 doses of MenC-CRM197(Meningitec; Wyeth Corporation Delaware, Madison, NJ) + DTPa-HBV-IPV/Hib (N = 93). At 13-14 months of age, Hib-MenC-TT and MenC-TT primed groups received a Hib-MenC-TT booster dose and the MenC-CRM primed group a booster dose of DTPa-HBV-IPV/Hib. Blood samples were taken before and at 1 and 18 months postbooster.

RESULTS

Before the booster dose, persistence of anti-polyribosyl ribitol phosphate (PRP) antibody concentration > or =0.15 microg/mL in the Hib-MenC-TT (96.4%) and MenC-TT (96.1%) primed groups and of MenC bactericidal titers > or =1:8 in the Hib-MenC-TT primed group (96.3%) was statistically significantly higher than in the MenC-CRM primed group (86.4% and 85.4%, respectively). One month after the Hib-MenC-TT booster, 99.2% subjects in the Hib-MenC-TT primed + MenC-TT primed pooled groups had anti-PRP levels > or =1 microg/mL, and 99.6% had SBA-MenC titers > or =1:128. The Hib-MenC-TT booster tended to be less reactogenic than the DTPa-HBV-IPV/Hib control and no serious adverse events related to vaccination were reported. Eighteen months after boosting with Hib-MenC-TT, SBA-MenC titers > or =1:8 persisted in 92.7% subjects and anti-PRP > or =0.15 microg/mL persisted in 99.4%.

CONCLUSIONS

Primary immunization with 3 doses of Hib-MenC-TT coadministered with DTPa-HBV-IPV induced antibodies that persisted up to the second year of life. The Hib-MenC-TT booster administered to primed toddlers induced robust and persistent antibody responses to both the Hib and MenC components and had an acceptable safety profile.

Antibody persistence and booster vaccination during the second and fifth years of life in a cohort of children who were born prematurely

BACKGROUND

These studies assessed the immunogenicity and reactogenicity of booster vaccination with diphtheria-tetanus-acellular pertussis-hepatitis B-inactivated poliovirus-adsorbed conjugated Haemophilus influenzae type b (DTaP-HBV-IPV/Hib) at 18-20 months, and with DTaP during the fifth year of life in children who had been born prematurely (<37 weeks gestation).

METHODS

Open-label, parallel group studies in which preterm and full-term subjects primed with DTaP-HBV-IPV/Hib received booster vaccination with DTaP-HBV-IPV/Hib (Infanrix hexa) at 18-20 months and DTaP (Infanrix) at 4 years of age. Immunogenicity was assessed before and 1 month after DTaP-HBV-IPV/Hib dose and 1 month after DTaP administration. Local and general symptoms were recorded for 4 days, unsolicited symptoms for 31 days after each dose.

RESULTS

Before the second year booster, Hib, hepatitis-B, and polio type 3 seroprotection rates were higher in the full-term group (antipolyribosyl ribitol phosphate > or =0.15 microg/mL observed in 76.2%/83.6% preterm/full term respectively, anti-HBs > or =10 mIU/mL in 75.0%/80.6% respectively). One month after the DTaP-HBV-IPV/Hib booster, > or =98% in both groups were seroprotected/seropositive for all vaccine antigens, except hepatitis-B in preterms (seroprotection rate 91.6%). By the fifth year hepatitis-B seroprotection rates were 85.3%/70.5% (preterm/full term) in subjects who had previously responded to hepatitis-B vaccination, and seroprotection rates for polio and polyribosyl ribitol phosphate were >95%. No differences between groups were observed after the DTaP booster. Both booster doses were generally well tolerated with minimal differences observed between groups. Local symptoms occurred more frequently after the fifth vaccination at 4 years of age.

CONCLUSIONS

Despite trends for lower immune responses to some vaccine antigens in preterm subjects, these findings support undelayed primary and booster vaccination in infants and children born before term. Booster vaccinations with DTaP-HBV-IPV/Hib and DTaP were well tolerated in this susceptible group.

Active immunization of premature and low birth-weight infants: a review of immunogenicity, efficacy, and tolerability

Preterm infants are at increased risk of disease and hospitalization from a number of vaccine-preventable diseases. However, these same infants have immunologic immaturities that may impact vaccine responses. Larger premature infants mount immune responses to vaccines similar to those of full-term infants, but very premature infants (<28-32 weeks' gestation at birth) may have specific defects in vaccine responsiveness. Although there are minor differences in immunogenicity, the immune responses to diphtheria, tetanus, pertussis, and polio antigens are similar enough between full-term and premature infants that clinical consequences are unlikely to result. However, the immunogenicity of Haemophilus influenzae type b conjugate vaccines varies widely among studies of premature infants, and may be affected by the choice of conjugate protein, inclusion in a combination vaccine, and by an infant's overall health. Pneumococcal conjugate vaccine is efficacious in larger premature infants, but little information is available about immunogenicity in smaller premature infants. Meningococcal group C conjugate vaccine appears immunogenic in even very premature infants, but the duration of immunity may be limited. Hepatitis B vaccine given at birth appears poorly immunogenic in infants with birth weights <1500-2000 g, with delay in the administration of the first dose yielding improved immunogenicity. Few data on influenza vaccine in premature infants are available, but infants with pulmonary disease may respond less robustly than others. Bacille Calmette Guérin vaccine appears to be most immunogenic if delayed until at least 34-35 weeks' postmenstrual age in very premature infants, although there may be non-specific advantages to its earlier administration. Premature infants may have persistently lower antibody titers than full-term infants, even years after initial immunization. Sick premature infants experience increased episodes of apnea or cardiorespiratory compromise following vaccine administration, necessitating careful monitoring. Specific factors that impair immune response, quality of the immune response, and safety and immunogenicity evaluation of new vaccines in premature infants are topics needing further research. Premature infants are at significant risk for decisions from healthcare providers that delay beginning and completing their vaccine regimens. A major challenge facing those who care for these infants is the provision of timely immunization.