Antibody response to accelerated Hib immunisation in preterm infants receiving dexamethasone for chronic lung disease

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

Vaccinations of premature infants are often delayed despite being at an increased risk of contracting vaccine preventable diseases. This article reviews the current knowledge on the immune response to widely used vaccines, on the protection derived from routine immunization and on vaccine safety and tolerability in a population of preterm infants. Available data evaluating the immune response of preterm infants support early immunization without correction for gestational age. For a number of antigens, the antibody response to initial doses of vaccines may be lower than that of term infants, but protective concentrations are often achieved and memory successfully induced. Vaccines are immunogenic, safe and well tolerated in preterm infants. Preterm infants should be vaccinated using the same schedules as those usually recommended for full-term infants, with the exception of the hepatitis B vaccine, where additional doses should be administered in infants receiving the first dose during the first days of life if they weighed less than 2000 g because of a documented reduced immune response.

Challenges in immunisation against bacterial infection in children

Polysaccharide-encapsulated organisms such as S. pneumoniae, H. influenzae type b and N. meningitidis are the leading causes of serious invasive bacterial diseases and pneumonia in children. The use of conjugate vaccines in developed countries has markedly decreased the burden of disease and mortality from these organisms through direct protection of the immunised and through herd immunity. Although conjugate vaccines are highly immunogenic, antibody levels after immunisation in early infancy wane, leading to the need for programmes which include booster doses. Understanding the generation of long-term immunity could lead to improvements in vaccine formulation and scheduling with the ultimate goal of providing more sustained protection. Prematurity is a risk factor for disease caused by polysaccharide-encapsulated bacteria and the available data indicate that preterm infants should be immunised according to their chronological age to provide early protection.

Parents' attitudes to neonatal research involving venepuncture

The objective of the study was to explore parental experiences of being offered participation in a previous neonatal research study involving venepuncture. The method employed was a questionnaire-based exploration of parents' attitudes in those approached to participate in a study of term and preterm immunization responses (Preterm Immunisation Study [PREMIS]). We explored experience of the initial approach, knowledge of study, venepuncture and views on research ‘in general’. In all, 59% of families responded. Highest response rates were for those participating in PREMIS (87% term/69% preterm) and lowest in decliners (34% and 35%). Responding parents participating in PREMIS were well informed, positive about research and did not find the venepuncture problematic. Sixty percent of responding parents who declined PREMIS attributed their declining to the need for venepuncture. In conclusion, parents participating or declining a neonatal study involving venepuncture are different, but participating parents were well informed and seemed able to judge that participation was right for them such that in consenting families venepuncture itself is not problematic.

Heptavalent pneumococcal conjugate vaccine immunogenicity in very-low-birth-weight, premature infants

BACKGROUND

The heptavalent pneumococcal CRM197 conjugate vaccine (PCV-7) has been incompletely studied in very-low-birth-weight (< or =1500 g) infants.

OBJECTIVE

To assess PCV-7 immunogenicity in very-low-birth-weight, premature infants. We hypothesized that the frequency of postvaccine antibody concentrations > or =0.15 microg/mL would vary directly with birth weight.

METHODS

This was a multicenter observational study. Infants 401 to 1500 g birth weight and <32 0/7 weeks gestation, stratified by birth weight, were enrolled from 9 National Institute of Child Health and Human Development Neonatal Research Network centers. Infants received PCV-7 at 2, 4, and 6 months after birth and had blood drawn 4 to 6 weeks following the third dose. Antibodies against the 7 vaccine serotypes were measured by enzyme-linked immunosorbent assay.

RESULTS

Of 369 enrolled infants, 244 completed their primary vaccine series by 8 months and had serum obtained. Subjects were 27.8 +/- 2.2 (mean +/- standard deviation) weeks gestation and 1008 +/- 282 g birth weight. Twenty-six percent had bronchopulmonary dysplasia and 16% had received postnatal glucocorticoids. Infants 1001 to 1500 g birth weight were more likely than those 401 to 1000 g to achieve antibody concentrations > or =0.15 microg/mL against the least 2 immunogenic serotypes (6B: 96% vs. 85%, P = 0.003 and 23F: 97% vs. 88%, P = 0.009). In multiple logistic regression analysis, lower birth weight, postnatal glucocorticoid use, lower weight at blood draw, and Caucasian race were each independently associated with antibody concentrations <0.35 microg/mL against serotypes 6B and/or 23F.

CONCLUSIONS

When compared with larger premature infants, infants weighing < or =1000 g at birth have similar antibody responses to most, but not all, PCV-7 vaccine serotypes.

[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.

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

BACKGROUND

Prematurity may be a risk factor for Haemophilus influenzae type b vaccine failure. This article evaluates the Haemophilus influenzae type b immunogenicity of a hexavalent diphtheria-tetanus-acellular pertussis-hepatitis B-inactivated poliovirus/Haemophilus influenzae type b vaccine in preterm infants (< 37 weeks' gestation).

METHODS

This was an open-label, parallel group study. Preterm (N = 94) and term infants (N = 92) received 3 doses of a diphtheria-tetanus-acellular pertussis-hepatitis B-inactivated poliovirus/Haemophilus influenzae type b vaccine at 2, 4, and 6 months with a booster dose at 18 to 20 months. Antipolyribosyl ribitol phosphate antibody concentrations were determined in serum samples taken before and 1 month after primary and booster vaccination.

RESULTS

Postprimary seroprotection rates (antipolyribosyl ribitol phosphate > or = 0.15 microg/mL) were lower in preterm than in term infants (92.5% vs 97.8%), with antipolyribosyl ribitol phosphate geometric mean concentrations of 2.241 vs 4.247 microg/mL. A progressive reduction in immune response to the Haemophilus influenzae type b antigen was observed with decreasing length of gestation and decreasing birth weight when cutoff > or = 1 microg/mL was considered. Prebooster seroprotection rates and antipolyribosyl ribitol phosphate geometric mean concentrations were low in both groups (antipolyribosyl ribitol phosphate > or = 1.0 microg/mL in 10.7% of preterm and 28.4% of term infants). A vigorous response to booster vaccination was seen in both groups, with no differences in postbooster seroprotection rates or antipolyribosyl ribitol phosphate geometric mean concentrations between the 2 groups (antipolyribosyl ribitol phosphate > or = 1.0 microg/mL in 100% of preterm and 98.5% of term infants).

CONCLUSIONS

Primary vaccination with a hexavalent diphtheria-tetanus-acellular pertussis-hepatitis B-inactivated poliovirus/Haemophilus influenzae type b vaccine at 2, 4, and 6 months with a booster dose at 18 to 20 months elicits a satisfactory antipolyribosyl ribitol phosphate response in preterm infants compared with term controls. Immunologic response decreased with decreased gestational age and birth weight.

Vaccination for the paediatrician

In most of Australia, general practitioners manage routine childhood vaccination schedules. However, paediatricians have an important role and need to have a thorough understanding of vaccination, particularly as it interfaces with other medical care. This is challenging as the Australian Standard Vaccination Schedule has undergone some substantial changes over the past 4 years, with the addition of meningococcal C conjugate, 7 valent pneumococcal conjugate, varicella and inactivated polio vaccines. Paediatricians are frequently the first port of call for advice on vaccination schedules for children with special needs, in relation to either vaccine efficacy or the risk of side effects. Categories include children with a range of chronic diseases, immunosuppression, premature infants and immigrant children. Advice about specific vaccines such as varicella, inactivated polio, influenza or multivalent vaccines and revaccination after adverse events is also often sought. The aim of this article is to update paediatricians on vaccination recommendations and relevant reference sources. The first part of this article discusses groups with special vaccination requirements. The second part discusses the use of individual vaccines in these children.

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.

Haemophilus influenzae type b immunization in infants in the United Kingdom: effects of diphtheria/tetanus/acellular pertussis/Hib combination vaccine, significant prematurity, and a fourth dose

OBJECTIVE

To measure anti-polyribosylribitolphosphate (PRP) antibody and anti-tetanus toxoid (TT) antibody responses in UK infants to explore the effects of (1) immunization with an acellular diphtheria/tetanus/pertussis/Haemophilus influenzae type b (DTPHib) combination vaccine, (2) significant preterm delivery, and (3) a fourth dose of conjugated Hib vaccine (PRP-T) in those with a low anti-PRP antibody (<1.0 microg/mL) after primary immunization.

METHODS

A prospective study was conducted in 4 tertiary neonatal units at a time when 2 types of DTPHib vaccines were used interchangeably in the United Kingdom for primary immunization: acellular (DTPaHib) and whole cell. Timing and type of all vaccine doses were as per standard UK practice. Blood was taken before and after immunization. A total of 166 preterm and 45 term infants completed the study; 97 (15 term) infants who had anti-PRP antibody <1.0 microg/mL were offered a fourth dose of PRP-T; 61 (55 preterm) then had repeat antibody measurements. Anti-PRP and anti-TT antibody after primary immunization relative to gestation and number of whole cell vaccine doses received was measured, as well as anti-PRP antibody after a fourth dose of PRP-T.

RESULTS

A total of 49% of preterm and 33% of term infants had anti-PRP antibody <1.0 microg/mL after full primary immunization. Receipt of 1 or more acellular vaccine doses was associated with lower anti-PRP antibody, a dose response effect being observed. Preterm infants were less likely to have anti-PRP antibody >1.0 microg/mL compared with term infants. A total of 93% of infants who were given a fourth dose had anti-PRP antibody >1.0 microg/mL. Anti-TT antibody responses were satisfactory for all infants but also reduced by each DTPaHib dose received.

CONCLUSION

Infants who receive DTPaHib, are significantly preterm, or who do not receive a fourth dose of conjugated Hib vaccine may be at increased risk for Hib disease.

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.

Dexamethasone inhibits maturation and alters function of monocyte-derived dendritic cells from cord blood

Critically ill infants are treated with dexamethasone (Dx) and other glucocorticoids to reduce inflammation and to promote lung and cardiac function. The neonatal immune system is immature, so neonatal dendritic cells (DCs) might be especially sensitive to glucocorticoid-mediated immunosuppression. To test this, we compared Dx treatment of monocyte-derived DCs from cord (CB) and adult blood (AB). Dx decreased CD1a levels on both AB and CB DCs. CB-treated cells also exhibited decreased expression of CD83 and increased expression of CD14, alterations not observed in AB DCs. Characteristic immature endocytic activity was sustained and enhanced in Dx-treated CB DCs, whereas AB DCs matured normally. Maintenance of endocytosis corresponded with CD14 expression. Dx markedly increased CB DC IL-10, a T cell helper 2 (Th2)-preferential cytokine, while reducing IL-12, a counterbalancing Th1 cytokine. AB DCs were also affected, but increases in IL-10 and decreases in IL-12 were more modest. Dx treatment also inhibited DC-induced T cell proliferation, but CB DCs were inhibited more. In short, neonatal DCs seemed to be especially sensitive to the immunosuppressive effects of Dx as indicated by altered phenotype, endocytic function, ability to stimulate T cells, and cytokine shift favoring Th2. These alterations in DC function are consistent with an increased risk for certain infections and atopic diseases.

Overproduction of corticotropin-releasing hormone blocks germinal center formation: role of corticosterone and impaired follicular dendritic cell networks

Corticotropin-releasing hormone (CRH) is a central mediator in the response to stress, coordinating behavioral, autonomic and neuroendocrine activation. CRH overproduction is implicated in several affective disorders, including major depression, panic-anxiety disorder and anorexia--diseases also associated with altered immune function. We investigated the link between CRH overdrive and immune function using CRH transgenic mice. Following immunization, CRH transgenic mice fail to form germinal centers; chronic glucocorticoid administration recapitulates this effect in wild-type mice. Regulation of germinal centers by glucocorticoids appears to be mediated, in part, through effects on follicular dendritic cells (FDC), providing a novel mechanism by which CRH dysregulation may significantly impair humoral immune responses.

Dexamethasone selectively inhibits differentiation of cord blood stem cell derived-dendritic cell (DC) precursors into immature DCs

Perinatal dexamethasone (Dx) alters the immune system leading to increased infections and developmental abnormalities. Dendritic cells (DCs) derived from cord-blood monocytes are especially Dx sensitive and we sought to determine the effects of Dx on cord-blood CD34+-DCs. Distinct stages of cord-blood CD34+-DC development were delineated: pre-DC, immature, and mature DCs. Dx added during development of pre-DCs did not suppress precursor number, or translocate the glucocorticoid receptor (GcR) from the cytoplasm to the nucleus. However, Dx added during pre-DCs differentiation into immature DCs, prompted GcR translocation to the nucleus, enhanced DC apoptosis, suppressed differentiation to CD1a+ cells, inhibited expression of CD86, reduced subsequent CD83 expression, maintained DC endocytic activity, suppressed IL-6 secretion, enhanced IL-10 secretion, and reduced DC-mediated T cell stimulation. Dx added during the maturation stage caused less dramatic effects. Thus, Dx stalled maturation, selectively induced apoptosis of developing DCs and the sensitivity peaked during pre-DCs differentiation into immature DCs.

Antibody response to diphtheria-tetanus-pertussis immunization in preterm infants who receive dexamethasone for chronic lung disease

OBJECTIVE

To study the effect of dexamethasone in preterm infants with chronic lung disease (CLD) on antibody response to routine immunization against diphtheria, tetanus, and pertussis (DTP).

METHODS

Serum samples were obtained before and after immunization with DTP (Trivax-AD) from an unselected cohort of 93 preterm infants in the United Kingdom. Antibodies to diphtheria and tetanus and to 4 pertussis antigens (pertussis toxin, filamentous hemagglutinin, pertactin, and fimbrial agglutinogens 2 + 3) were measured by an enzyme-linked immunosorbent assay. Linear regression models were fitted to the natural log of antibody titers to compare the dexamethasone-treated and -untreated infants adjusting for potential risk factors.

RESULTS

Sixty-seven (72%) of 93 infants received dexamethasone. Preimmunization geometric mean titers (GMTs) were comparable in both groups for all antibodies. The rise in GMT after immunization was reduced in the dexamethasone-treated group. Final GMT was significantly lower for tetanus, diphtheria, pertussis toxin, and fimbrial agglutinogens 2 + 3 but not for filamentous hemagglutinin or pertactin. Using the minimum protective titer of 0.01 IU/mL, there was no significant reduction in protection for diphtheria and tetanus in the dexamethasone-treated infants. Using the higher reference titer of 0.1 IU/mL, there was a 16% reduction in protection for diphtheria (95% confidence interval: 3%-27%) and a 9% reduction in protection for tetanus (95% confidence interval: -7% to 20%).

CONCLUSIONS

The use of dexamethasone for CLD in preterm infants is associated with a reduction in antibody titer to routine immunization against diphtheria and tetanus. Antibody responses to 2 of 4 pertussis antigens are reduced, but the clinical significance of this observation is unclear. Protection against tetanus and diphtheria is not impaired when the lower reference value for protective antibody is used. On the basis of this study of UK preterm infants who were treated with dexamethasone for the management of CLD, we conclude that the current DTP immunization schedule is adequate and do not recommend additional booster protection against tetanus or diphtheria during early infancy. When diphtheria prevalence is increased, however, additional protection should be considered.

Acellular pertussis vaccine given by accelerated schedule: response of preterm infants

OBJECTIVE

To describe the immune response of preterm infants to a diphtheria/tetanus/three component acellular pertussis (DTaP) vaccine, under an accelerated schedule, and the effects of steroids on this response. To compare responses with those of term infants.

DESIGN

Prospective observational study.

SETTING

Five Wessex neonatal units; Hertfordshire immunisation clinics.

PATIENTS

Infants born at < 32 weeks; term controls.

INTERVENTIONS

DTaP-Haemophilus influenzae type b vaccine given at 2, 3, and 4 months. Blood taken to assess antibody responses to vaccines.

MAIN OUTCOME MEASURES

IgG geometric mean concentrations (GMC) to vaccines.

RESULTS

A total of 130 preterm (mean gestational age 29.1 weeks) and 54 term infants were recruited. After the third immunisation, preterm infants had similar GMCs to controls to diphtheria, tetanus, filamentous haemagglutinin (FHA), and pertactin (PRN), but a significantly lower GMC to pertussis toxin (PT). Responses to tetanus and PRN increased with age at the third immunisation, and those to tetanus, FHA, PRN, and PT increased with gestational age at birth. Response to tetanus correlated negatively with the number of doses of antenatal steroids received. There was no association between responses and postnatal steroids.

CONCLUSION

When immunised with a combined acellular pertussis- H influenzae type b vaccine under an accelerated schedule, IgG GMC of preterm infants to PT was reduced. GMCs to tetanus, FHA, PRN, and PT increased with gestational age at birth, and GMCs to tetanus and PRN increased with age at the third immunisation. There is, however, no benefit in delaying immunisation. Anti-tetanus IgG decreased with increasing number of doses of antenatal steroids. There was no effect for postnatal steroids.

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.

Effect of a fourth Haemophilus influenzae type b immunisation in preterm infants who received dexamethasone for chronic lung disease

AIM

To assess whether a fourth Hib polysaccharide-tetanus protein conjugate vaccine (PRP-T) would improve antibody response in preterm infants previously treated with dexamethasone for chronic lung disease.

METHODS

In a pilot study 12 infants born at less than 30 weeks gestation who had received corticosteroids were given a supplementary Hib dose six weeks after completion of the primary immunisation course. Serum samples obtained before and at eight weeks following the fourth Hib dose were analysed for total level and avidity of anti-PRP antibody.

RESULTS

There was no significant increase in the geometric mean titre (GMT) of anti-PRP antibody resulting from the fourth Hib immunisation (GMT: pre 2.35 micro g/ml, post 2.24 micro g/ml, p = 0.79). A subgroup of six infants had subprotective antibody levels (<1.0 micro g/ml) after the primary immunisation course, which remained subprotective following the extra Hib immunisation. Despite the poor response in total antibody level, the study group showed a significant rise in PRP specific IgG avidity following the fourth immunisation (GMAI: pre 0.076, post 0.138, p = 0.043).

CONCLUSION

An additional Hib immunisation given to recently steroid treated preterm infants six weeks after completion of the primary schedule did not augment primary immunogenicity. However, increasing avidity may imply successful priming and long term immunity to Hib.

Postnatal glucocorticosteroid therapy for treatment and prevention of neonatal chronic lung disease

Neonatal chronic lung disease (CLD) is a persistent complication, primarily of premature infants. Postnatal glucocorticoid therapy is widely used in the treatment and prevention of CLD. Most studies reveal acute improvement in the pulmonary status of infants treated with postnatal glucocorticoid therapy. Recent studies of 'earlier' intervention (< 14 days of age) demonstrated a reduction in mortality and in the occurrence of CLD between 28 days of age and 36 weeks postmenstrual age. Great concern remains, however, regarding the potential adverse outcomes, including growth inhibition, infection, catastrophic GI complications and CNS injury. Therefore, the use of postnatal glucocorticoid therapy remains controversial with respect to the clinical indications for initiating therapy, the dose, duration, onset and route of administration, as well as potential benefits and risks. Inhaled glucocorticoid therapy is increasingly used to treat and prevent CLD in order to avoid adverse effects of high dose systemic glucocorticoid therapy. Recent studies with inhaled glucocorticoid therapy show promise. Further work, however, for improving aerosol delivery and deposition, will be needed to refine their role in the prevention and treatment of CLD. Future studies enabling early, accurate identification of infants at greatest risk for CLD, coupled with a more comprehensive understanding of the different pathogeneses, will provide information regarding appropriate timing of onset, dosing, route of therapy and duration of intervention.