Systemic and local immune responses to enhanced-potency inactivated poliovirus vaccine in premature and term infants

Immune correlates of protection by mRNA-1273 vaccine against SARS-CoV-2 in nonhuman primates

Immune correlates of protection can be used as surrogate endpoints for vaccine efficacy. Here, nonhuman primates (NHPs) received either no vaccine or doses ranging from 0.3 to 100 μg of the mRNA-1273 severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccine. mRNA-1273 vaccination elicited circulating and mucosal antibody responses in a dose-dependent manner. Viral replication was significantly reduced in bronchoalveolar lavages and nasal swabs after SARS-CoV-2 challenge in vaccinated animals and most strongly correlated with levels of anti–S antibody and neutralizing activity. Lower antibody levels were needed for reduction of viral replication in the lower airway than in the upper airway. Passive transfer of mRNA-1273–induced immunoglobulin G to naïve hamsters was sufficient to mediate protection. Thus, mRNA-1273 vaccine–induced humoral immune responses are a mechanistic correlate of protection against SARS-CoV-2 in NHPs.

Protective antibodies elicited by SARS-CoV-2 spike protein vaccination are boosted in the lung after challenge in nonhuman primates

Protein subunit–based vaccines have been used extensively for protection against viral infections. Here, Francica et al. tested a protein subunit vaccine for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The authors vaccinated nonhuman primates with soluble prefusion-stabilized spike trimers (preS dTM) plus the adjuvant AS03, an oil-in-water emulsion. The authors found that preS dTM plus AS03 induced robust antibody and cellular immune responses that protected nonhuman primates from disease when challenged with SARS-CoV-2. This rapid protection, with increases in antibodies specific to spike protein observable as soon as 2 days after infection, provides evidence of a critical anamnestic antibody response. Antibodies elicited by preS dTM vaccination are protective against SARS-CoV-2 in nonhuman primates.

Adjuvanted soluble protein vaccines have been used extensively in humans for protection against various viral infections based on their robust induction of antibody responses. Here, soluble prefusion-stabilized spike protein trimers (preS dTM) from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) were formulated with the adjuvant AS03 and administered twice to nonhuman primates (NHPs). Binding and functional neutralization assays and systems serology revealed that the vaccinated NHP developed AS03-dependent multifunctional humoral responses that targeted distinct domains of the spike protein and bound to a variety of Fc receptors mediating immune cell effector functions in vitro. The neutralizing 50% inhibitory concentration titers for pseudovirus and live SARS-CoV-2 were higher than titers for a panel of human convalescent serum samples. NHPs were challenged intranasally and intratracheally with a high dose (3 × 10⁶ plaque forming units) of SARS-CoV-2 (USA-WA1/2020 isolate). Two days after challenge, vaccinated NHPs showed rapid control of viral replication in both the upper and lower airways. Vaccinated NHPs also had increased spike protein–specific immunoglobulin G (IgG) antibody responses in the lung as early as 2 days after challenge. Moreover, passive transfer of vaccine-induced IgG to hamsters mediated protection from subsequent SARS-CoV-2 challenge. These data show that antibodies induced by the AS03-adjuvanted preS dTM vaccine were sufficient to mediate protection against SARS-CoV-2 in NHPs and that rapid anamnestic antibody responses in the lung may be a key mechanism for protection.

Immune Correlates of Protection by mRNA-1273 Immunization against SARS-CoV-2 Infection in Nonhuman Primates

Immune correlates of protection can be used as surrogate endpoints for vaccine efficacy. The nonhuman primate (NHP) model of SARS-CoV-2 infection replicates key features of human infection and may be used to define immune correlates of protection following vaccination. Here, NHP received either no vaccine or doses ranging from 0.3 - 100 μg of mRNA-1273, a mRNA vaccine encoding the prefusion-stabilized SARS-CoV-2 spike (S-2P) protein encapsulated in a lipid nanoparticle. mRNA-1273 vaccination elicited robust circulating and mucosal antibody responses in a dose-dependent manner. Viral replication was significantly reduced in bronchoalveolar lavages and nasal swabs following SARS-CoV-2 challenge in vaccinated animals and was most strongly correlated with levels of anti-S antibody binding and neutralizing activity. Consistent with antibodies being a correlate of protection, passive transfer of vaccine-induced IgG to naïve hamsters was sufficient to mediate protection. Taken together, these data show that mRNA-1273 vaccine-induced humoral immune responses are a mechanistic correlate of protection against SARS-CoV-2 infection in NHP.

One-Sentence Summary

mRNA-1273 vaccine-induced antibody responses are a mechanistic correlate of protection against SARS-CoV-2 infection in NHP.

Vaccination with SARS-CoV-2 Spike Protein and AS03 Adjuvant Induces Rapid Anamnestic Antibodies in the Lung and Protects Against Virus Challenge in Nonhuman Primates

Adjuvanted soluble protein vaccines have been used extensively in humans for protection against various viral infections based on their robust induction of antibody responses. Here, soluble prefusion-stabilized spike trimers (preS dTM) from the severe acute respiratory syndrome coronavirus (SARS-CoV-2) were formulated with the adjuvant AS03 and administered twice to nonhuman primates (NHP). Binding and functional neutralization assays and systems serology revealed that NHP developed AS03-dependent multi-functional humoral responses that targeted multiple spike domains and bound to a variety of antibody FC receptors mediating effector functions in vitro. Pseudovirus and live virus neutralizing IC50 titers were on average greater than 1000 and significantly higher than a panel of human convalescent sera. NHP were challenged intranasally and intratracheally with a high dose (3×106 PFU) of SARS-CoV-2 (USA-WA1/2020 isolate). Two days post-challenge, vaccinated NHP showed rapid control of viral replication in both the upper and lower airways. Notably, vaccinated NHP also had increased spike-specific IgG antibody responses in the lung as early as 2 days post challenge. Moreover, vaccine-induced IgG mediated protection from SARS-CoV-2 challenge following passive transfer to hamsters. These data show that antibodies induced by the AS03-adjuvanted preS dTM vaccine are sufficient to mediate protection against SARS-CoV-2 and support the evaluation of this vaccine in human clinical trials.

Dysregulated Mucosal Immunity and Associated Pathogeneses in Preterm Neonates

Many functions of the immune system are impaired in neonates, allowing vulnerability to serious bacterial, viral and fungal infections which would otherwise not be pathogenic to mature individuals. This vulnerability is exacerbated in compromised newborns such as premature neonates and those who have undergone surgery or who require care in an intensive care unit. Higher susceptibility of preterm neonates to infections is associated with delayed immune system maturation, with deficiencies present in both the innate and adaptive immune components. Here, we review recent insights into early life immunity, and highlight features associated with compromised newborns, given the challenges of studying neonatal immunity in compromised neonates due to the transient nature of this period of life, and logistical and ethical obstacles posed by undertaking studies newborns and infants. Finally, we highlight how the unique immunological characteristics of the premature host play key roles in the pathogenesis of diseases that are unique to this population, including necrotizing enterocolitis and the associated sequalae of lung and brain injury.

Common Queries About Immunizations in Preterm Infants

Preterm infants are at an increased risk of morbidity and mortality from vaccine-preventable diseases. Despite this, delays in routine immunization of preterm infants are common. Available guidelines clearly state that they should be immunized according to chronological age, irrespective of gestational age and birth weight or current weight. In this article, we try to assuage parental and provider doubts by reviewing data about immunogenicity, safety, and responses to routine immunizations in preterm infants with and without comorbidities. We also look at evidence for other strategies to help protect this fragile population. [Pediatr Ann. 2018;47(4):e147-e153.].

Immunogenicity of Two Different Sequential Schedules of Inactivated Polio Vaccine Followed by Oral Polio Vaccine Versus Oral Polio Vaccine Alone in Healthy Infants in China

BACKGROUND

Two vaccination schedules where inactivated polio vaccine (IPV) was followed by oral polio vaccine (OPV) were compared to an OPV-only schedule.

METHODS

Healthy Chinese infants received a 3-dose primary series of IPV-OPV-OPV (Group A), IPV-IPV-OPV (Group B), or OPV-OPV-OPV (Group C) at 2, 3, and 4 months of age. At pre-Dose 1, 1-month, and 14-months post-Dose 3, polio 1, 2, and 3 antibody titers were assessed by virus-neutralizing antibody assay with Sabin or wild-type strains. Adverse events were monitored.

RESULTS

Anti-polio 1, 2, and 3 titers were ≥8 (1/dil) in >99% of participants, and Group A and Group B were noninferior to Group C at 1-month post-Dose 3 as assessed by Sabin strain-based assay (SSBA). In Group A 1-month post-Dose 3, there was no geometric mean antibody titers (GMT) differences for types 1 and 3; type 2 GMTs were ≈3-fold higher by wild-type strain-based assay (WTBA) versus SSBA. For Group B, GMTs were ≈1.7- and 3.6-fold higher for types 1 and 2 via WTBA, while type 3 GMTs were similar. For Group C, GMTs were ≈6.3- and 2-fold higher for types 1 and 3 with SSBA, and type 2 GMTs were similar. Antibodies persisted in >96.6% of participants. Adverse event incidence in each group was similar.

CONCLUSIONS

A primary series of 1 or 2 IPV doses followed by 2 or 1 OPV doses was immunogenic and noninferior to an OPV-only arm. SSBA was better at detecting antibodies elicited by OPV with antibody titers correlated to the number of OPV doses (NCT01475539).

Vaccine schedule compliance among very low birth weight infants in Lima, Peru

OBJECTIVE

There is little information about vaccine schedule compliance in very-low-birth-weight infants in developing countries. The aim of the study was to describe the compliance with the vaccine schedule among this population in Lima, Peru.

PATIENTS AND METHODS

We conducted a prospective cohort study in four hospitals in Lima in infants with a birth-weight of less than 1500 g, followed from birth up to 12 months of age every 2 weeks. The date and age at administration of each vaccine was recorded

RESULTS

222 infants were enrolled. The median birth-weight was 1250 g (range 550-1499 g) and the median gestational age was 30.0 weeks (range 23-37 weeks). The mean age for the first pentavalent (DPT, Hib, HepB) and oral polio vaccine administration was 4.3 ± 1.4 months in infants with a birth-weight of < 1000 g vs. 3.1 ± 1.0 in infants with a birth-weight 1000-1500 g (p < 0.001); 4.1 ± 0.9 vs. 3.3 ± 1.1 for rotavirus (p < 0.05); and 5.1 ± 2.1 vs. 4.3 ± 1.8 for the 7-valent pneumococcal conjugated vaccine. Only 35% had received the three doses of oral polio and pentavalent vaccine by seven months, although by nine months 81% had received these vaccines.

CONCLUSIONS

Vaccination of very-low-birth-weight infants in Peru is significantly delayed, especially in infants with a birth-weight of < 1000 g and lower gestational age. Urgent educational interventions targeting physicians and nurses should be implemented in order to improve vaccination rates and timing in these high risk populations.

Immunization in special populations

In summary, immunizations in special populations require understanding the underlying disease and how it might affect the immune system's ability to mount an antibody response to vaccines or predispose certain patient populations to developing certain serious infections. There is still a great need for research on the optimal timing of vaccines after transplants, how to assess protection and development of a protective antibody response after immunization, and whether certain groups (eg, HIV) need to be revaccinated after a certain amount of time if their antibody levels decline. In addition, there are limited data on efficacy of the newer vaccines in these special patient populations, which also requires further investigation.

Evaluation of vaccine coverage for low birth weight infants during the first year of life in a large managed care population

OBJECTIVE

There are few recent population-based assessments of vaccine coverage in premature infants available. This study assesses and compares age- and dose-specific immunization coverage in children of different birth weight categories during the first year of life.

METHODS

We performed a retrospective cohort analysis of computerized vaccination data from a large managed care organization in southern California. The participants were children born between January 1, 1997, and December 31, 2002, and continuously enrolled from birth to at least 12 months of age in the Southern California Kaiser Permanente health plan. We measured age-specific up-to-date and age-appropriate immunization rates according to birth weight (extremely low birth weight: <1000 g; very low birth weight: 1000-1499 g; low birth weight: 1500-2499 g; normal birth weight: >/=2500 g) for 4 vaccines (hepatitis B, diphtheria and tetanus toxoids with pertussis, Haemophilus influenzae type b, and poliovirus) through the first year of life.

RESULTS

We identified 127 833 infants born during the study period and continuously enrolled through the first year of life; 120 048 were normal birth weight infants; 6491 were low birth weight infants; 788 were very low birth weight infants; and 506 were extremely low birth weight infants. Vaccine-specific age-appropriate immunization rates were 3% to 15% lower for low birth weight infants and 17% to 33% lower for extremely low birth weight infants compared with the rates for normal birth weight infants in the first 6 months of life. Extremely low birth weight infants had the lowest age-specific up-to-date immunization levels (5%-31% lower) compared with normal birth weight infants at each age assessed. By 12 months, extremely low birth weight infants still had significantly lower up-to-date levels (87%) compared with very low birth weight, low birth weight, and normal birth weight infants (91%-92%).

CONCLUSIONS

Despite recommendations that lower birth weight infants be vaccinated as the same chronological age as normal birth weight infants, extremely low birth weight and very low birth weight infants are immunized at significantly lower rates relative to low birth weight and normal birth weight infants at 2, 4, and 6 months of age. However, by 12 months of age this finding persists only in extremely low birth weight infants.

[Immunization of the preterm infant]

Premature infants have an increased risk of experiencing infectious diseases, some of which are vaccine preventable diseases. Maturation of immune responses begins with exposition to environmental antigens and in premature infants as fast as in term-infants. Premature infants must be vaccinated at 2 months of age, whatever the gestational age. Acellular Pertussis vaccine and pneumococcal conjugate vaccine must be given as early as possible, at two months of age. Immunization schedule in premature infants is the same as in full-term infants : three injections one month apart with a pentavalent vaccine : Diphteria, Tetanus, Poliomyelitis, Pertussis and Haemophilus type b. First injection of hepatitis B vaccine must not be taken in account when this vaccine is given at birth to infants under 2 kg birth weight. Premature infants 6 months of age or older and experiencing chronic lung disease have to be vaccinated against influenza. In all cases, surroundings have to be vaccinated. Apnea and/or bradycardia have been reported within the 48 hours following vaccination in premature infants before 32 weeks of gestational age and justify giving their first injection of vaccine under cardiorespiratory monitoring. These injections will be given before discharge as often as possible.

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.

Measles-mumps-rubella and varicella vaccine responses in extremely preterm infants

OBJECTIVE

Extremely preterm infants mount lower antibody responses than term infants to several vaccines. The objective of this study was to measure the immunogenicity of measles-mumps-rubella and varicella vaccines in preterm and term children.

METHODS

Immune status before immunization and immune response after immunization with measles-mumps-rubella and varicella vaccines at 15 months of age were compared in 32 infants, 16 of whom were preterm (< 29 weeks' gestation) and 16 of whom were term (> or = 37 weeks' gestation) at birth. Blood was drawn before vaccination and 3 to 6 weeks thereafter. Measles antibody was measured by plaque reduction neutralization assay. Mumps and rubella immunoglobulin G were measured in available sera by enzyme-linked fluorescent immunoassay. Varicella immunoglobulin G was measured in available sera by glycoprotein enzyme-linked immunosorbent assay. Values that were above or below the assay limits were assigned values double or half those limits, respectively. The primary outcome was the geometric mean antibody titer.

RESULTS

Preterm children had lower mumps and rubella geometric mean titers than did term children before vaccine, and nearly all children were seronegative for each of the 4 vaccine antigens before immunization. Measles, mumps, rubella, and varicella geometric mean titers were similar between groups after vaccine. All children were seropositive for measles after vaccine, whereas 13 of 14 preterm and 11 of 13 term children were seropositive for mumps, 13 of 14 preterm and 13 of 13 term children were seropositive for rubella, and 11 of 16 preterm and 9 of 15 term children were seropositive for varicella.

CONCLUSIONS

Preterm children mounted antibody responses that were similar to those of term children after measles-mumps-rubella and varicella vaccines at 15 months of age.

Immunisation of premature infants

Premature infants are at increased risk of vaccine preventable infections, but audits have shown that their vaccinations are often delayed. Early protection is desirable. While the evidence base for immunisation of preterm infants is limited, the available data support early immunisation without correction for gestational age. For a number of antigens the antibody response to initial doses may be lower than that of term infants, but protective concentrations are often achieved and memory successfully induced. A 2-3-4 month schedule may be preferable for immunisation of preterm infants in order to achieve protection as early as possible, but an additional dose may be required to achieve persistence of protection. This update focuses on the use of routine childhood vaccines in premature infants.

Response of preterm newborns to immunization with a hexavalent diphtheria-tetanus-acellular pertussis-hepatitis B virus-inactivated polio and Haemophilus influenzae type b vaccine: first experiences and solutions to a serious and sensitive issue

OBJECTIVE

Preterm infants are at increased risk from infections and should be vaccinated at the usual chronological age. The aim of the study was to evaluate the immunogenicity and reactogenicity of a hexavalent diphtheria-tetanus-acellular pertussis-hepatitis B virus-inactivated polio and Haemophilus influenzae type b (DTPa-HBV-IPV/Hib) vaccine in preterm infants.

METHODS

In a comparative trial, 94 preterm infants between 24 and 36 weeks (mean +/- SD gestational age: 31.05 +/- 3.45 weeks; mean birth weight: 1420 +/- 600 g) and a control group of 92 full-term infants were enrolled to receive 3 doses of a DTPa-HBV-IPV/Hib vaccine at 2, 4, and 6 months. Immunogenicity was assessed in serum samples that were taken before and 4 weeks after primary vaccination. Evaluation of reactogenicity was based on diary cards.

RESULTS

All preterm (n = 93) and full-term (n = 89) infants who were included in the immunogenicity analysis had seroprotective titers to diphtheria; tetanus; and polio virus types 1, 2, and 3. The immune response to the Hib and hepatitis B components was lower in preterm than in full-term infants: 92.5% versus 97.8% and 93.4% versus 95.2%, respectively. Vaccine response rates for pertussis antigens were >98.9% in both study groups. Although most geometric mean titers were lower in preterm infants, titers were similar for pertussis, a major threat for premature infants. The vaccine was well tolerated, and there were no differences in reactogenicity between groups. Some extremely immature infants experienced transient cardiorespiratory events within the 72 hours after the first vaccination with no clinical repercussion.

CONCLUSIONS

Preterm infants who were immunized with the hexavalent DTPa-HBV-IPV/Hib vaccine at 2, 4, and 6 months displayed good immune response to all antigens. The availability of this vaccine greatly facilitates the vaccination of premature infants.

DT5aP-Hib-IPV and MCC vaccines: preterm infants' response to accelerated immunisation

AIMS

To describe the immune response of preterm infants to combined diphtheria/tetanus/5 component acellular pertussis-Haemophilus influenzae type b inactivated polio vaccine (DT5aP-Hib-IPV) and meningococcal serogroup C conjugate vaccine (MCC) under accelerated schedule. To compare results with term infants immunised with DT5aP-Hib-IPV and with historical data from preterm infants immunised with a DT3 component aP-Hib vaccine.

METHODS

Prospective observational study in preterm infants born at <32 weeks gestation with comparison to contemporary cohort of term infants. DT5aP-Hib-IPV and MCC vaccines were given at 2, 3, and 4 months.

RESULTS

Fifty preterm infants (mean gestational age 28.5 weeks) completed the study. After three doses of vaccines Hib polysaccharide IgG geometric mean concentration (GMC) was 1.21 microg/ml with 80% > or =0.15 microg/ml; MCC serum bactericidal assay geometric mean titre (GMT) was 1245 with 100% > or =8. All infants achieved protective titres to diphtheria, tetanus, and the three poliovirus types with > or =80% achieving protective rises in IgG against the five pertussis antigens.

CONCLUSION

Preterm infants immunised with DT5aP-Hib-IPV and MCC vaccines show IgG responses to Hib and MCC greater than seen historically in both term and preterm infants with a DT3aP-Hib vaccine, and for pertussis antigens and poliovirus type 1 responses similar to that seen in term infants immunised with DT5aP-Hib-IPV. Responses to poliovirus types 2 and 3 are reduced, but all infants achieved protective titres.

Immunization of preterm and low birth weight infants. American Academy of Pediatrics Committee on Infectious Diseases

Preterm (PT) infants are at increased risk of experiencing complications of vaccine-preventable diseases but are less likely to receive immunizations on time. Medically stable PT and low birth weight (LBW) infants should receive full doses of diphtheria, tetanus, acellular pertussis, Haemophilus influenzae type b, hepatitis B, poliovirus, and pneumococcal conjugate vaccines at a chronologic age consistent with the schedule recommended for full-term infants. Infants with birth weight less than 2000 g may require modification of the timing of hepatitis B immunoprophylaxis depending on maternal hepatitis B surface antigen status. All PT and LBW infants benefit from receiving influenza vaccine beginning at 6 months of age before the beginning of and during the influenza season. All vaccines routinely recommended during infancy are safe for use in PT and LBW infants. The occurrence of mild vaccine-attributable adverse events are similar in both full-term and PT vaccine recipients. Although the immunogenicity of some childhood vaccines may be decreased in the smallest PT infants, antibody concentrations achieved usually are protective.

Controversies in polio immunization

Vaccines against poliomyelitis have been in use for nearly five decades now and have played a major role in progress towards global eradication of the disease. Both the vaccines, (oral polio vaccine and inactivated polio vaccine) and their uses are still debated with particular reference to their selective advantages vs. disadvantages, choice for individual vs. community protection and their administration strategies. Further occurrence of vaccine associated paralytic poliomyelitis with oral vaccine assumes importance in the face of disappearing disease. Further availability of inactivated polio vaccine in India and its various schedules such as sequential and combination schedules show some promise for polio eradication.

Hib vaccination in infants born prematurely

AIMS

To document the immunogenicity and persistence of antibody to polyribosyl-ribitol phosphate (PRP) as well as the clinical protection against invasive Haemophilus influenzae type b (Hib) disease in premature infants immunised at the routine schedule.

METHODS

Blood was obtained at 2, 5, 12, and 64 months of age from a cohort of prematurely born infants (<or=32 weeks gestation). Anti-PRP antibody concentrations were compared with those of a control cohort of infants born at full term and vaccinated at the same schedule. Hib vaccine failures occurring between October 1992 and October 2000 were reported by paediatricians through an active, prospective, national survey in the UK and Republic of Ireland. The number of prematurely born children with vaccine failure was compared with the corresponding number born at term.

RESULTS

Twenty seven prematurely born infants were followed to 5 years of age. Compared with term infants they had a significantly lower geometric mean concentration of anti-PRP antibody and/or a significantly lower proportion above one or both of the conventional protective antibody concentrations (0.15 and 1.0 micro g/ml) at all ages. A total of 165 cases of invasive Hib disease were identified over eight years of national surveillance. Eighteen were premature (<37 weeks); approximately 12 would be expected. The relative risk of UK premature infants developing disease compared with term infants was 1.5 (95% CI 0.9 to 2.6).

CONCLUSIONS

Premature infants develop lower antibody concentrations than term infants following Hib conjugate vaccination. Premature infants may also have an increased risk of clinical vaccine failure, but interpretation is limited by the small number of premature infants developing invasive Hib disease over eight years of national surveillance. Overall, vaccination with Hib conjugate vaccines affords a high level of protection to premature babies.

Controlled trial of immune response of preterm infants to recombinant hepatitis B and inactivated poliovirus vaccines administered simultaneously shortly after birth

AIM

The study was conducted to evaluate the immunogenicity of an early, extra dose of enhanced inactivated poliovirus vaccine (IPV) administered simultaneously with recombinant hepatitis B vaccine (HBV) to preterm infants shortly after birth.

METHODS

Three groups were studied. Fifty preterm infants received IPV intramuscularly within 24 hours of birth, in addition to routine recommended childhood immunisations. Fifty two preterm infants and 35 full term infants received routine immunisations only (routine vaccination timing: HBV at birth, 1 and 6 months of age; IPV at 2 and 4 months; oral polio vaccine (OPV) at 4 and 6 months; diphtheria-tetanus-pertussis (DTP) at 2, 4, and 6 months; and Haemophilus influenzae B vaccine at 2 and 4 months). Blood samples were taken at birth, 3 and 7 months of age from all infants, and at 1 month of age from preterm infants only.

RESULTS

At birth, a lower percentage of both study and control preterm infants had antipoliovirus type 3 titres >/= 1:8 than full term infants. At 1 and 3 months of age significantly more early IPV infants had antipoliovirus type 3 titres >/= 1:8 than routinely vaccinated preterm infants (p < 0.05). At 7 months of age there were no significant differences in percentage of antipoliovirus titres >/= 1:8 or geometric mean times (GMTs) between the early IPV group and the routinely vaccinated preterm group. At 3 and 7 months of age, the percentage of positive antihepatitis B titres (>/= 1:10) and the GMT of the early IPV preterm group did not differ significantly from those of preterm controls. There was no significant difference in percentage of positive antihepatitis B titres between the early IPV group and full term controls at any time. GMTs for hepatitis B antibodies were significantly lower in the early IPV preterm group than in full term controls at 3 and 7 months of age.

CONCLUSIONS

Administration of an additional dose of IPV simultaneously with routine HBV to preterm infants shortly after birth provides early protection from poliovirus and hepatitis B infection, and does not interfere with poliovirus antibody production at the age of 7 months.

Safety and immunogenicity of an acellular pertussis vaccine in premature infants

OBJECTIVES

To evaluate the safety and immunogenicity of a two-component acellular pertussis vaccine in preterm infants.

STUDY DESIGN

Fifty preterm infants (25-35 weeks of gestation; mean, 30.8 weeks) and 50 term infants as a control group received a two-component acellular pertussis vaccine irrespective of their biological age and actual weight. Adverse reactions were registered by parents on a diary card and reviewed on each visit. Antibodies against pertussis toxoid (PT) and filamentous hemagglutinin (FHA) were determined with an enzyme-linked immunosorbent assay before the first and after the third vaccination.

RESULTS

The infants of both groups showed an increase in geometric mean titers (GMT) against PT and FHA after vaccination (3 doses). There was a significant difference of antibody concentration between the preterm and the control group. The GMT for PT antibody of the preterm infants was 64. 16 U/L, and for the term infants it was 98.96 U/L. The GMT for FHA was 50.92 U/L in preterm versus 86.02 U/L in the control group. Efficacy of the immunization (more than a fourfold increase of antibody concentration in each infant) was 93.5% in the preterm group with respect to PT and 82.6% with respect to FHA. The incidence of adverse reactions was low and comparable in both study groups.

CONCLUSION

Immunization with an acellular pertussis vaccine is safe for preterm infants. The immune response is significantly lower compared with a control group of term infants, but efficacy is high.

[Recommended vaccines and immunoglobulins for immunocompromised patients]

A revision of the literature was made as to the recommendations given for the use of vaccines and immune globulins in persons who presented total or partial immunodeficiency, mainly related to the nineties. The analysis of 75 references led to the following principal conclusions: the vaccines containing living agents are generally inappropriate for persons who present conditions which determine serious immunodeficiency; the vaccines which contain dead agents or only antigenic fractions, despite their being less immunogenic and conferring lower rates of protection to severely immunocompromised persons as compared to normal persons, are safe and should be administered to them. Immunocompromised patients should receive immune globulins for the same indications and in the same doses as immunocompetent persons, with the exception of immune globulin to prevent measles, as recommended in a dosage of 0.5 mL/Kg for immunodeficients (15 mL, maximum).

[The premature infant confronting community-acquired infections. Which prophylaxis?]

Preterm infants are at high risk of severe community acquired infections. In particular viral respiratory infections, mainly respiratory syncitial virus infections (RVS), are responsible for a high incidence of rehospitalizations of preterm infants during their 2 first years of life. Prevention relies upon 1/the application of an immunization program identical to the program applied to normal term infants, a cardiorespiratory monitoring during 48-72 hours following immunization being recommended in those infants who carry a risk of recurrent apnea; 2/general measures with a demonstrated protective effect, i.e., breast feeding, elimination of smoking at home, and when possible limitation of contacts with infant and children communities. Immunoprophylaxis against RVS infections has been shown to be effective in reducing the severity of RVS infections in preterm infants but is presently not available in European countries.

Inactivated poliovirus vaccine: past and present experience

Many countries have made use of inactivated poliovirus vaccine (IPV) in their national poliovirus control programs since 1955. Until 1961 IPV was the only vaccine available for the control of poliovirus, but subsequently many countries opted to use the Sabin attenuated poliovirus vaccine (OPV), which was perceived as more effective in preventing intestinal infection and in ensuring community protection by spreading to unvaccinated contacts of vaccinees. Nevertheless, IPV has remained the vaccine of choice in several countries, where experience has shown that it represents a safe and effective option for disease control. IPV limits subsequent infection of the pharynx and intestine in vaccinees, and is able to control circulation of poliovirus in a vaccinated population, providing effective community protection. Furthermore IPV contains only killed virus and cannot cause vaccine-associated paralytic poliomyelitis as OPV sometimes does. This paper reviews the history of the use of IPV, with emphasis on its efficacy and its ability to safely protect communities in which it is used. As the incidence of poliomyelitis declines new control strategies should take account of the knowledge of the use of poliovirus vaccines acquired since 1955.

Antibody response to Haemophilus influenzae type b capsular polysaccharide conjugated to tetanus toxoid in preterm infants

OBJECTIVE

To evaluate the antibody response to a Haemophilus influenzae type b capsular polysaccharide (HibCP) tetanus toxoid (TT) conjugate vaccine (HibCP-TT) in preterm infants.

SUBJECTS

Thirty-five healthy preterm infants with gestational ages (GA) from 27 to 36 weeks and birth weights from 920 to 2550 g. Controls were 37 term infants.

METHODS

All infants were immunized with HibCP-TT at 2, 4 and 12 months of age. Antibodies to HibCP and TT were determined at each immunization and 1 month after the second and third.

RESULTS

After two doses of HibCP-TT the preterm infants with GAs < or = 30 weeks (n = 8; mean GA, 29.5 weeks) had a significantly lower HibCP antibody response than the preterm infants with GAs > 30 weeks (n = 23; mean GA, 34.2 weeks) (P = 0.004), who for their part had a response not significantly different from that of the term infants. After the third dose there were no significant differences among the groups. The response to the TT part of the vaccine showed the same pattern.

CONCLUSION

Although the most immature infants may show an inadequate antibody response to the initial immunizations, many preterm infants can benefit from vaccination with HibCP-TT when starting immunization at the same chronologic age as term infants.

Early immunization with inactivated poliovirus vaccine in premature infants

The antibody titers of 41 premature infants receiving inactivated poliovirus vaccine at 2 months of age (control group) were compared with titers of 39 infants receiving an additional dose at 5 to 10 days of age (study group). At 1 month of age 97.4% of the study group but only 70.8% of the control group had protective antibodies against poliovirus 3 (p < 0.001).

Update on childhood immunizations

OBJECTIVE

To provide an overview of childhood immunizations with emphasis in new recommendations, as well as recent vaccine developments and special populations.

DATA SOURCES

English language literature identified via a MEDLINE search. Additional references were obtained from cited references.

STUDY SELECTION AND DATA EXTRACTION

Original articles, reviews, and official publications were used to obtain the most accurate data on safety and efficacy of available pediatric vaccines, as well as current recommendations for their use.

DATA SYNTHESIS

Immunizations have been an area of vigorous research for several years. New vaccines have been developed by improving older products to maximize immunogenicity and minimize adverse effects. Some of these novel vaccines, like the Haemophilus influenzae type b conjugate vaccines (HibCV), have already contributed significantly to the prevention of diseases in childhood. New recommendations have been issued to help speed this process. Adverse effects of routine immunizations are generally mild and transient.

CONCLUSIONS

The development of new effective and safe vaccines for children is an important step in the global eradication of contagious diseases. A new generation of combination vaccines has started with the combination of the diphtheria-tetanus-pertussis vaccine and HibCV. Some other combined products are yet to come that would eventually make immunization schedules more cost-effective and improve compliance rates. Our colleagues in the community and in the ambulatory care setting must actively participate in the implementation of vaccination programs and provide education to parents regarding all aspects of the immunization process.

Response to Haemophilus influenzae type b conjugate vaccine in chronically ill premature infants

Twenty-two premature infants with chronic lung disease (median gestational age 28 weeks) received polyribosylribitol phosphate-outer membrane protein conjugate Haemophilus vaccine at 2 and 4 months of chronologic age. The proportions with antibodies to polyribosylribitol phosphate at levels > 1 microgram/ml after doses 1 and 2 were 27% and 55%; geometric mean titers were 0.43 and 0.73 microgram/ml, significantly lower than values for term infants.