Frequency of apnea, bradycardia, and desaturations following first diphtheria-tetanus-pertussis-inactivated polio-Haemophilus influenzae type B immunization in hospitalized preterm infants

Penta- and hexavalent vaccination of extremely and very-to-moderate preterm infants born at less than 34 weeks and/or under 1500 g: A systematic literature review

Debate regarding vaccinating high-risk infants with penta- and hexavalent vaccines persists, despite their good immunogenicity and acceptable safety profile in healthy full-term infants. We report the findings of a systematic literature search that aimed to present data on the immunogenicity, efficacy, effectiveness, safety, impact, compliance and completion of penta- and hexavalent vaccination in high-risk infants, including premature newborns. Data from the 14 studies included in the review showed that the immunogenicity and the safety profile of penta- and hexavalent vaccines in preterm infants was generally similar to those seen in full-term infants, with the exception of an increase in cardiorespiratory adverse events such as apnea, bradycardia and desaturation following vaccination in preterm infants. Despite recommendations of vaccinating preterm infants according to their actual age, and the relatively high completion rate of the primary immunization schedule, vaccination was often delayed, increasing the vulnerability of this high-risk population to vaccine-preventable diseases.

Immunization of preterm infants: current evidence and future strategies to individualized approaches

Preterm infants are at particularly high risk for infectious diseases. As this vulnerability extends beyond the neonatal period into childhood and adolescence, preterm infants benefit greatly from infection-preventive measures such as immunizations. However, there is an ongoing discussion about vaccine safety and efficacy due to preterm infants' distinct immunological features. A significant proportion of infants remains un- or under-immunized when discharged from primary hospital stay. Educating health care professionals and parents, promoting maternal immunization and evaluating the potential of new vaccination tools are important means to reduce the overall burden from infectious diseases in preterm infants. In this narrative review, we summarize the current knowledge about vaccinations in premature infants. We discuss the specificities of early life immunity and memory function, including the role of polyreactive B cells, restricted B cell receptor diversity and heterologous immunity mediated by a cross-reactive T cell repertoire. Recently, mechanistic studies indicated that tissue-resident memory (Trm) cell populations including T cells, B cells and macrophages are already established in the fetus. Their role in human early life immunity, however, is not yet understood. Tissue-resident memory T cells, for example, are diminished in airway tissues in neonates as compared to older children or adults. Hence, the ability to make specific recall responses after secondary infectious stimulus is hampered, a phenomenon that is transcriptionally regulated by enhanced expression of T-bet. Furthermore, the microbiome establishment is a dominant factor to shape resident immunity at mucosal surfaces, but it is often disturbed in the context of preterm birth. The proposed function of Trm T cells to remember benign interactions with the microbiome might therefore be reduced which would contribute to an increased risk for sustained inflammation. An improved understanding of Trm interactions may determine novel targets of vaccination, e.g., modulation of T-bet responses and facilitate more individualized approaches to protect preterm babies in the future.

Major cardiorespiratory events do not increase after immunizations, eye exams, and other stressors in most very low birth weight infants

BACKGROUND

Increased cardiorespiratory events with bradycardia and oxygen desaturation have been reported in very low birthweight (VLBW) infants following stressors such as immunizations. These events are difficult to quantify and may be mild. Our group developed an automated algorithm to analyze bedside monitor data from NICU patients for events with bradycardia and prolonged oxygen desaturation (BDs) and used this to compare BDs 24 hours before and after potentially stressful interventions.

METHODS

We included VLBW infants from 2012-2017 with data available around at least one of four interventions: two-month immunizations, retinopathy of prematurity (ROP) examinations, ROP therapy, and inguinal hernia surgery. We used a validated algorithm to analyze electrocardiogram heart rate and pulse oximeter saturation data (HR, SpO2) to quantify BD events of HR <  100 beats/minute for≥4 seconds with oxygen desaturation <  80%SpO2 for≥10 seconds. BDs were analyzed 24 hours before and after interventions using Wilcoxon rank-sum tests.

RESULTS

In 354 of 493 (72%) interventions, BD frequency stayed the same or decreased in the 24 hours after the event. An increase of at least five BD's occurred in 17/146 (12%) after immunizations, 85/290 (29%) after ROP examinations, 4/33 (12%) after ROP therapy, and 3/25 (12%) after hernia surgery. Infants with an increase in BDs after interventions had similar demographics compared to those without. More infants with an increase in BDs following immunizations were on CPAP or caffeine than those without.

CONCLUSIONS

Most VLBW infants in our cohort had no increase in significant cardiorespiratory events in the 24 hours following potentially stressful interventions.

Cardiorespiratory Events Following the Second Routine Immunization in Preterm Infants: Risk Assessment and Monitoring Recommendations

Due to frequent cardiorespiratory events (CREs) in response to the first routine immunization (rIM), current guidelines recommend readmitting and monitoring extremely preterm infants after the second rIM, though evidence on CREs in response to the second rIM is weak. In a prospective observational study, preterm infants with an increase in CREs after the first rIM were monitored for CREs before and after the second rIM. Seventy-one infants with a median gestational age of 26.4 weeks and a median weight of 820 g at birth were investigated at a median postnatal age of 94 days. All but seven infants showed an increase in CREs after the second rIM. The frequency of hypoxemias (p < 0.0001), apneas (p = 0.0003) and cardiorespiratory events requiring tactile stimulation (CRE-ts) (p = 0.0034) increased significantly. The 25 infants (35%) presenting with CRE-ts were significantly more likely to have been continuously hospitalized since birth (p = 0.001) and to receive analeptic therapy at the first rIM (p = 0.002) or some kind of respiratory support at the first (p = 0.005) and second rIM (p < 0.0001). At a postmenstruational age of 43.5 weeks, CRE-ts ceased. Our data support the recommendation to monitor infants who fulfil the above-mentioned criteria during the second rIM up to a postmenstruational age of 44 weeks.

Update on vaccination of preterm infants: a systematic review about safety and efficacy/effectiveness. Proposal for a position statement by Italian Society of Pediatric Allergology and Immunology jointly with the Italian Society of Neonatology

INTRODUCTION

Preterm infants (PIs) are at increased risk of vaccine-preventable diseases (VPDs). However, delayed vaccination start and low vaccine coverage are still reported. Areas covered: This systematic review includes 37 articles on preterm vaccination published in 2008-2018 in PubMed. Both live attenuated and inactivated vaccines are safe and well tolerated in PIs. Local reactions, apnea, and reactivity changes are the most frequently reported adverse events. Lower gestational age and birth weight, preimmunization apnea, longer use of continuous positive airway pressure (CPAP) are risk factors for apnea. The proportion of PIs who develop protective humoral and cellular immunity is generally similar to full terms although later gestational age is associated with increased antibody IgG concentrations (i.e. against certain pneumococcal serotypes, influenza, hepatitis B virus and poliovirus 1) and increased mononuclear cells proliferation (i.e. after inactivated poliovirus). Expert opinion: PIs can be safely and adequately protected by available vaccines with the same schedule used for full terms. Data at this regard have been retrieved by studies using a 3-dose primary series for pneumococcal and hexavalent vaccines. Further studies are needed regarding the 2 + 1 schedule. Apnea represents a nonspecific stress response in PIs, thus those hospitalized at 2 months should have cardio-respiratory monitoring after their first vaccination.

Randomized Controlled Trial on the Effects of Morning versus Evening Primary Vaccination on Episodes of Hypoxemia and Bradycardia in Very Preterm Infants

BACKGROUND

Hypoxemia and bradycardia occur frequently in preterm infants, but are incompletely understood. They are more prevalent during infections and following immunization. Data on adults suggested an increased immune response if subjects slept following vaccination, suggesting an interaction between circadian rhythm and the immune system. Whether this holds true for preterm infants with their less well-established circadian rhythm is unclear.

OBJECTIVE

Do infants born at 26-30 weeks' gestation and having received their first routine hexavalent vaccination in the morning have a lower cardiorespiratory event rate (CER) after vaccination than those receiving it in the evening?

METHODS

Twenty-six infants were randomized to an evening versus morning vaccination group in a pilot and main study with 10 and 16 participants, respectively. Pulse oximeter saturation, actigraphy, and rectal temperature were obtained for 24 h before and after vaccination. Blood samples for vaccination titers were taken before vaccination and during a follow-up examination in our outpatient clinic; another blood sample was taken 24 h after vaccination to determine inflammatory markers.

RESULTS

Vaccination led to an increase in CER in both groups, but there was no difference in CER between the morning and evening groups. Vaccination titers for Bordetella pertussis were increased in both groups, with no difference in inflammatory markers 24 h after vaccination. Body temperature increased in both groups after vaccination. Participants in the evening group slept longer after vaccination.

CONCLUSIONS

We did not identify a difference in CER between morning and evening vaccination but could confirm increased body temperatures and vaccination titers following vaccination.

Clinical and experimental aspects of breathing modulation by inflammation

Neuroinflammation is produced by local or systemic alterations and mediated mainly by glia, affecting the activity of various neural circuits including those involved in breathing rhythm generation and control. Several pathological conditions, such as sudden infant death syndrome, obstructive sleep apnea and asthma exert an inflammatory influence on breathing-related circuits. Consequently breathing (both resting and ventilatory responses to physiological challenges), is affected; e.g., responses to hypoxia and hypercapnia are compromised. Moreover, inflammation can induce long-lasting changes in breathing and affect adaptive plasticity; e.g., hypoxic acclimatization or long-term facilitation. Mediators of the influences of inflammation on breathing are most likely proinflammatory molecules such as cytokines and prostaglandins. The focus of this review is to summarize the available information concerning the modulation of the breathing function by inflammation and the cellular and molecular aspects of this process. I will consider: 1) some clinical and experimental conditions in which inflammation influences breathing; 2) the variety of experimental approaches used to understand this inflammatory modulation; 3) the likely cellular and molecular mechanisms.

Quality Improvement Project to Reduce Delayed Vaccinations in Preterm Infants

BACKGROUND

Preterm infants are especially vulnerable to infectious diseases. Although vaccinations are a safe and effective measure to protect preterm infants from vaccine-preventable diseases, delays in vaccinations are not uncommon.

PURPOSE

The goal of this quality improvement project was to improve on time vaccinations of preterm infants hospitalized in the neonatal intensive care unit.

METHODS

The Plan-Do-Study-Act model of quality improvement was adopted to develop, test, and implement interventions aimed at improving timely vaccination of preterm infants. The primary outcome measure of interest was the rate of on time vaccination, which was defined as the proportion of medically eligible preterm infants who received vaccinations within 2 weeks of the recommended schedule.

RESULTS

Baseline on time vaccination rate was only 36%. Following several Plan-Do-Study-Act cycles, a steady increase in on time vaccinations of eligible infants was observed, and a new baseline on time vaccination rate of 82% was achieved.

IMPLICATIONS FOR PRACTICE

Simple interventions implemented within the context of Plan-Do-Study-Act cycles are effective in improving timely vaccinations among preterm infants.

IMPLICATIONS FOR RESEARCH

Future research that focuses on vaccinations in preterm infants is needed to further reinforce the safety and efficacy of vaccines. Effective methods on how to disseminate and apply this knowledge to practice should also be studied.Video Abstract available at http://links.lww.com/ANC/A27.

Frequently asked questions on seven rare adverse events following immunization

Routine mass immunization programs have contributed greatly to the control of infectious diseases and to the improvement of the health of populations. Over the last decades, the rise of antivaccination movements has threatened the advances made in this field to the point that vaccination coverage rates have decreased and outbreaks of vaccine-preventable diseases have resurfaced. One of the critical points of the immunization debate revolves around the level of risk attributable to vaccination, namely the possibility of experiencing serious and possibly irreversible adverse events. Unfortunately, the knowledge about adverse events, especially rare ones, is usually incomplete at best and the attribution of a causal relationship with vaccinations is subject to significant uncertainties. The aim of this paper is to provide a narrative review of seven rare or very rare adverse events: hypotonic hyporesponsive episode, multiple sclerosis, apnea in preterm newborns, Guillain-Barré syndrome, vasculitides, arthritis/ arthralgia, immune thrombocytopenic purpura. We have selected these adverse events based on our experience of questions asked by health care workers involved in vaccination services. Information on the chosen adverse events was retrieved from Medline using appropriate search terms. The review is in the form of questions and answers for each adverse event, with a view to providing useful and actionable concepts while not ignoring the uncertainties that remain. We also highlight in the conclusion possible future improvements to adverse event detection and assessment that could help identify individuals at higher risk against the probable future backdrop of ever-greater abandonment of compulsory vaccination policies.

Respiratory Decompensation and Immunization of Preterm Infants

BACKGROUND

Concern for respiratory decompensation after immunization in premature infants, particularly those with bronchopulmonary dysplasia (BPD), may lead to delayed and altered immunization schedules.

METHODS

A retrospective cohort of premature infants at <32 weeks' gestational age cared for in a tertiary level 4 NICU and immunized during their hospital stay were evaluated for respiratory decompensation within 72 hours of immunization. Respiratory measurements including change in respiratory support, mean fraction of inspired oxygen, and apnea, bradycardia, and desaturation events were compared between those infants with BPD and those without. The primary outcome was the difference in respiratory decompensation defined as a composite of increased respiratory support or increased fraction of inspired oxygen ≥10% within 72 hours of immunization.

RESULTS

Of 403 infants admitted to the NICU and immunized, 240 met the study criteria. Of those infants, 172 had a diagnosis of BPD. There was no difference in the primary outcome of respiratory decompensation after immunization between groups (P = .65). There was also no significant difference in apnea, bradycardia, and desaturation events between groups (P = .51).

CONCLUSIONS

In this cohort, respiratory decompensation requiring clinical intervention after immunization of preterm infants both with and without BPD was uncommon and not significantly different between groups. Consideration for immunization of this vulnerable population should not be delayed out of concern for clinical deterioration.

Delayed start of diphtheria, tetanus, acellular pertussis and inactivated polio vaccination in preterm and low birth weight infants in the Netherlands

BACKGROUND

It is recommended that preterm (PT) and low birth weight infants be vaccinated according to standard guidelines. We studied the timeliness of the first diphtheria, tetanus, acellular pertussis and inactivated polio vaccination in the Netherlands, by gestational age (GA) and birth weight (BW).

METHODS

We included all vaccinated children born during 2006-2010. Data from the national immunization register were used to determine the vaccination age and the proportion of timely vaccinated infants (<70 days). Results were compared between groups based on GA (extreme PT: <32, PT: 32-36, full term (FT): ≥37 weeks) and BW. Characteristics associated with the timeliness of vaccination were studied by Cox regression analyses.

RESULTS

The median vaccination age was lower with a higher GA/BW. The proportion of timely vaccinated infants was 66% for extreme PT, 76% for PT and 82% for FT infants. Similar results were seen by BW. Overall, the proportion of timely vaccinated infants increased from 2006 (77%) until 2010 (85%) and there were regional differences and differences by ethnicity. In extreme PT and PT infants, living in a very highly urbanized municipality and being light for GA were associated with less timely vaccination. Being vaccinated in a hospital was associated with a timelier vaccination in extreme PT infants. However, the reverse was seen for PT infants.

CONCLUSIONS

In the Netherlands, PT and low birth weight infants were less often timely vaccinated than FT infants and were, therefore, at increased risk of vaccine-preventable infections. In FT infants, the timeliness of vaccination is better but could also be optimized.

Incidence of catheter-related bloodstream infections in neonates following removal of peripherally inserted central venous catheters

OBJECTIVES

Catheter-associated bloodstream infections are a significant source of morbidity and healthcare cost in the neonatal ICU. Previous studies examining the prevalence of bloodstream infections after removal of peripherally inserted central venous catheters in neonates are equivocal.

DESIGN

A retrospective cohort study.

PATIENTS

All infants with peripherally inserted central venous catheters treated at the Vanderbilt neonatal ICU between 2007 and 2009.

MEASUREMENTS AND MAIN RESULTS

We evaluated the following outcomes: 1) bloodstream infections, 2) culture-negative sepsis, 3) number of sepsis evaluations, and 4) number of significant apnea/bradycardia events comparing odds ratios between 72 hours before and 72 hours after peripherally inserted central venous catheter removal. We analyzed a total of 1,002 peripherally inserted central venous catheters in 856 individual infants with a median (interquartile range) gestational age of 31 weeks (28-37 wk) and a median birth weight of 1,469 g (960-2,690 g). Comparing 72 hours before with 72 hours after peripherally inserted central venous catheter removal did not show a difference in the prevalence of bloodstream infections (9 vs 3, p = 0.08), prevalence of culture-negative sepsis (37 vs 40, p = 0.73), number of sepsis evaluations (p = 0.42), or number of apnea/bradycardia events (p = 0.32). However, in peripherally inserted central venous catheter not used for delivery of antibiotics, there was a 3.83-fold increase in odds for culture-negative sepsis following peripherally inserted central venous catheter removal (95% confidence interval, 1.48-10.5; p = 0.001). For infants less than 1,500 g birth weight (very low birth weight), odds for culture-negative sepsis increased to 6.3-fold following removal of peripherally inserted central venous catheters not used for antibiotic delivery (95% confidence interval, 1.78-26.86; p < 0.01).

CONCLUSIONS

Although these data do not support the routine use of antibiotics for sepsis prophylaxis prior to peripherally inserted central venous catheter removal, they suggests that very low birth weight infants not recently exposed to antibiotics are at increased odds for associated adverse events following discontinuation of their peripherally inserted central venous catheter.

Possible predictors of cardiorespiratory events after immunization in preterm neonates

BACKGROUND

The influence of the first immunization on cardiorespiratory (CR) stability in very preterm infants is still a controversial subject.

OBJECTIVES

To describe the changes induced by immunization on heart and respiratory rate variability (HRV-RRV) and to test a potential association between preimmunization profiles and postimmunization CR events.

METHODS

Continuous 72-hour CR recordings and 2.5-hour polysomnographic recordings were performed on very preterm infants immunized after 7 weeks. The results are expressed as medians (interquartile ranges).

RESULTS

Immunization was performed on 31 very preterm infants [28 weeks' gestation (26.9-29), birth weight: 965 g (795-1,105)], and was associated with an increased incidence (p < 0.01) of events lasting more than 10 s: bradycardia <80 bpm [2.2 (1.1-7) vs. 1.8 (1-4)/12 h], desaturation [17.6 (9.4-36.4) vs. 13.9 (7.7-33.8)/12 h] and associated bradycardia-desaturation [IB+D, 4.1 (1.4-7.3) vs. 2.4 (1-4.6)/12 h], with mild changes in HRV and no change in RRV. The changes in IB+D frequency were correlated with preimmunization IB+D frequency (r = 0.44, p < 0.05), HRV spectral parameter low frequency/high frequency ratio (LF/HF, r = 0.55, p < 0.01) and approximate entropy of HRV (r = -0.39, p < 0.05).

CONCLUSION

The increase in CR events after the first immunization in very preterm infants was associated with: (1) sympathetic predominance in heart rate control (high LF/HF ratio), (2) abnormal oversimplification of HRV (low entropy) and (3) persistent respiratory rhythm control immaturity (high IB+D before vaccine).

Frequency of respiratory deterioration after immunisation in preterm infants

AIM

To determine the relationship between the initiation of respiratory support and the first routine immunisation of neonates at 2 months of age during primary hospitalisation.

METHODS

An historical cohort study design was used to study the neonatal factors associated with the initiation of respiratory support within 7 days of immunisation in a cohort of 7629 preterm and term infants admitted to the Neonatal Unit of the Royal Women's Hospital between 2001 and 2008.

RESULTS

The 411 infants who received their first immunisations in hospital were both very preterm and of extremely low birth weight (ELBW, below 1000 g). Twenty-two infants experienced post-immunisation apnoea of sufficient severity to warrant the initiation of either intermittent positive pressure ventilation (two cases) or continuous positive airway pressure (20 cases). Infants exhibiting a respiratory deterioration following immunisation had a higher incidence of previous septicaemia (Odds ratio 2.5, 95% confidence interval 1.0, 6.1; P = 0.04) and received CPAP for a longer period prior to vaccination (P = 0.03).

CONCLUSION

Apnoea following immunisation may be an aetiological factor in the requirement of respiratory support in a small number of preterm, ELBW infants particularly those with significant lung disease and those who have previously experienced septicaemia.

Risk of fever and sepsis evaluations after routine immunizations in the neonatal intensive care unit

OBJECTIVE

Premature infants can experience cardiorespiratory events such as apnea after immunization in the neonatal intensive care unit (NICU). These changes in clinical status may precipitate sepsis evaluations. This study evaluated whether sepsis evaluations are increased after immunizations in the NICU.

STUDY DESIGN

We conducted a retrospective cohort study of infants older than 53 days who were vaccinated in the NICU at the KPMCP (Kaiser Permanente Medical Care Program). Chart reviews were carried out before and after all immunizations were administered and for all sepsis evaluations after age 53 days. The clinical characteristics of infants on the day before receiving a sepsis evaluation were compared between children undergoing post-immunization sepsis evaluations and children undergoing sepsis evaluation at other times. The incidence rate of sepsis evaluations in the post-immunization period was compared with the rate in a control time period not following immunization using Poisson regression.

RESULT

A total of 490 infants met the inclusion criteria. The rate of fever was increased in the 24 h period after vaccination (2.3%, P<0.05). The incidence rate of sepsis evaluations was 40% lower after immunization than during the control period, although this was not statistically significant (P=0.09). Infants undergoing a sepsis evaluation after immunization were more likely to have an apneic, bradycardic or moderate-to-severe cardiorespiratory event in the day before the evaluation than were infants undergoing sepsis evaluations at other times (P<0.05).

CONCLUSION

Despite an increase in fever and cardiorespiratory events after immunization in the NICU, routine vaccination was not associated with increased risk of receiving sepsis evaluations. Providers may be deferring immunizations until infants are clinically stable, or may have a higher threshold for initiating sepsis evaluations after immunization than at other times.

Immunisation practices in infants born prematurely: neonatologists' survey and clinical audit

AIM

To determine Australian neonatologists' recommendations for the immunisation of ex-preterm infants and compare their actual immunisation status with recommended Australian guidelines.

METHODS

A self-administered nine-part questionnaire of current immunisation practices was sent to all Neonatologists in Australia (2006). A complementary retrospective immunisation audit was conducted in two tertiary neonatal units in Melbourne. Hospital records and the Australian Childhood Immunisation Register (ACIR) were reviewed; consenting parents were interviewed and primary care physicians' vaccination records were requested. A random sample of preterm infants born between July 2003 and June 2005 at <32 weeks' gestation were selected.

RESULTS

(i) Neonatologists Survey: The response rate was 68% and the majority of neonatologists (89%) were aware of the current guidelines, but adherence to them varied from 43% to 79%. One-fifth of neonatologists personally do not receive annual influenza vaccination; and (ii) Immunisation Audit: Conducted between October 2006-May 2007 it included: 100 hospital records; 97 ACIR records; 47 parent interviews and 43 primary care vaccination records. Overall vaccination coverage was 90% at 12 months of age. Only 20% (10/50) of infants with chronic lung disease received an influenza vaccination. Vaccines were delayed by greater than one month in 15% of participants for the 2 month DTPa vaccine and 43% at 6 months.

CONCLUSIONS

The neonatologists survey highlighted variable adherence with immunisation guidelines. The audit confirmed preterm infants are frequently experiencing delayed vaccination and recommended additional vaccinations are often not being received. Formulation of strategies to ensure complete and timely immunisation are required, including better utilisation of the ACIR.

Recurrence of cardiorespiratory events following repeat DTaP-based combined immunization in very low birth weight premature infants

We evaluated the tolerance to immunization of 64 very low birth weight preterm infants. Thirty-three of the infants experienced a cardiorespiratory event after the first vaccination, and 6 of these 33 (18%) had a recurrence after the second vaccination, including 2 infants previously discharged to home. A cardiorespiratory event associated with the first vaccination was the sole risk factor for recurrence identified.

Absence of an increase in cardiorespiratory events after diphtheria-tetanus-acellular pertussis immunization in preterm infants: a randomized, multicenter study

OBJECTIVE

The American Academy of Pediatrics recommends immunization of preterm infants at 2 months' chronological age with diphtheria-tetanus-acellular pertussis vaccine, regardless of birth weight and gestational age. Several investigators have reported an increased incidence of cardiorespiratory events in preterm infants after immunization. Consequently, many primary care providers do not adhere to American Academy of Pediatrics guidelines. The purpose of this study was to reexamine the relationship between diphtheria-tetanus-acellular pertussis and cardiorespiratory events in preterm infants by using a random control study design and an objective assessment of cardiorespiratory events.

METHODS

Ten hospitals enrolled 191 infants who were born at <37 weeks' gestational age at 56 to 60 days' chronological age. Infants were randomly assigned to a group that received diphtheria-tetanus-acellular pertussis immunization (n = 93) or a control group that did not (n = 98). Recording monitors were used continuously during the next 48 hours to document prolonged apnea and prolonged bradycardia. The presence and number of episodes during the 48-hour period were compared between groups by using chi(2) and t tests.

RESULTS

In the diphtheria-tetanus-acellular pertussis group, 16.1% experienced at least 1 episode of prolonged apnea compared with 20.4% of control infants. One or more prolonged bradycardia events occurred in 58.1% of immunized infants and 56.1% of the control infants. The frequency of episodes was not significantly different between groups. The immunization group and the control group each had an average of 0.5 episodes of prolonged apnea. The mean number of prolonged bradycardia episodes was 2.6 in the immunization group and 2.7 in the control group.

CONCLUSIONS

Preterm infants who received diphtheria-tetanus-acellular pertussis at 2 months after birth were no more likely to experience prolonged apnea and bradycardia than were control infants. This study supports the American Academy of Pediatrics recommendation regarding diphtheria-tetanus-acellular pertussis immunization at 2 months of age for preterm infants.