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AAP Grand Rounds 18:61-62 (2007)
© 2007 American Academy of Pediatrics
The AAP recommends immunization of premature infants at two months of postnatal age1,2 Investigators at the University of Tennessee sought to determine the incidence of cardiorespiratory complications and abnormal C-reactive protein (CRP) responses of infants following immunization with single vaccine compared with multiple vaccines given simultaneously.
Investigators enrolled a convenience sample of eligible premature infants of at least two months postnatal age who were still in the NICU and were scheduled to receive their first routine immunizations. Subjects were assigned to receive a single randomly chosen vaccine (DTaP, Hib, HBV, IPV, or PCV7) or multiple separate vaccines simultaneously. Infants receiving a single vaccine were given the remaining vaccines three days after administration of the single vaccine, but only the reaction to the first vaccine was studied. All infants were given acetaminophen before vaccination and for 48 hours thereafter.
Cardiorespiratory monitoring and pulse oximetry were used to detect apnea, bradycardia, or oxygen desaturation episodes during the three days following vaccination. CRP was measured every 12 hours following immunization for a total of three. If CRP values became abnormal following immunization, they were repeated daily until normal. CRP values were considered abnormal if >1.6 mg/dL.
During the study period, 239 eligible premature infants received immunization: 168 infants received a single vaccine and 71 received multiple vaccines. The mean gestational age at birth was 28 weeks. Over 90% had bronchopulmonary dysplasia, apnea of prematurity, gastroesophageal reflux, or intraventricular hemorrhage (grade 3 or 4). In the group receiving multiple immunizations, 82% received all five vaccines.
Nearly one in three preterm infants receiving multiple vaccines had an adverse cardiorespiratory event within 48 hours after immunization (32%). Of infants experiencing adverse cardiorespiratory events, two-thirds required initiation of, or increase in, supplemental oxygen and the remainder required CPAP, assisted ventilation, or an increase in ventilator settings. Ninety-five percent of such adverse events occurred within 48 hours of immunization.
Among infants receiving single vaccines, the rate of such events was 22% after DTaP, 12% after PCV7, 11% after Hib, 3% after IPV, and 0% after HBV. Using logistic regression analysis, the authors identified a nearly significant association between the risk of adverse cardiorespiratory events and receipt of multiple vaccines compared with any single vaccine (OR 3.62; 95% CI, 0.99–13.25). Elevated CRP values followed immunization in 85% of infants who received multiple vaccines; among infants receiving single vaccines, the rate of abnormal CRP elevation was 70% after Hib, 54% after PCV7, 24% after DTaP, and 0% after IPV and HBV. CRP elevation was not related to adverse cardiorespiratory events. The authors concluded that multiple immunizations are associated with adverse cardiorespiratory events but that such events also can occur following single vaccines, particularly DTaP, and that precautionary monitoring is indicated for 48 hours following immunization.
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Commentary by
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| Pediatric Practice, Nampa, ID |
The authors found a higher incidence of significant adverse cardiorespiratory events than has been reported in some previous studies, probably because this study population was composed of sicker, smaller babies. These results are applicable to premature infants still hospitalized at two months of age, many of whom have significant comorbidity such as apnea of prematurity and gastroesophageal reflux.
The finding that multiple vaccines entailed higher risk of adverse cardiorespiratory events compared with single vaccine administration is problematic because the multiple vaccine group was compared with the five single vaccine groups combined. The single vaccine groups had varying rates of adverse cardiorespiratory events (0% to 22%) and were of different sizes (26–44 children per group).
Comparison with such a heterogeneous group means little. However, there is no suggestion of adverse interaction between vaccines. Most of the risk associated with multiple vaccines is accounted for by the DTaP vaccine, and in fact, the risks in the multiple vaccine and DTaP groups did not differ significantly (32% vs 22%; OR 1.70; 95% CI, 0.65–4.58). Moreover, the observed risk of cardiorespiratory events after multiple vaccines (32%) was less than the expected overall risk if all five vaccines were given separately (41% assuming no interaction). The finding of adverse cardiorespiratory events after DTaP, Hib, or PCV7 given alone differs from data presented in the AAP guidelines1,2 but is supported by other studies summarized by the authors.
Clearly, among more premature infants, immunization is associated with cardiorespiratory adverse events. Such morbidity must be weighed against the benefits of immunization among this very vulnerable group of children. The authors’ conclusion in favor of monitoring this population for at least 48 hours following immunization is certainly justified and is consistent with AAP guidelines.
| Editors’ Note |
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| References |
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