Risk of Pertussis in Relation to Degree of Prematurity in Children Less Than 2 Years of Age

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Abstract

Background:

A few previous studies reported increased risk of pertussis in children with birth weight less than 2500 g. The risk of pertussis by degree of prematurity has not been determined in a cohort study. The vaccine effectiveness (VE) against reported pertussis in preterm infants is unknown.

Methods:

Data were obtained from the Medical Birth Registry of Norway (1998–2010) and linked to other national registries. In total, 713,166 children were included in our study and followed until 2 years of age. Incidence rate ratios (IRRs) and confidence intervals (CIs) were estimated with Poisson regression.

Results:

We identified 999 reported cases of pertussis. We observed a higher rate of reported pertussis in preterm than in full-term infants, IRR = 1.65 (95% CI: 1.32–2.07). Compared to full-term infants, the risk of reported pertussis in infants born at gestational age (GA) 35–36, 32–34 and 23–27 weeks were higher [IRRs = 1.49 (95% CI: 1.11–2.01), 1.63 (95% CI: 1.06–2.51) and 4.49 (95% CI: 2.33–8.67), respectively]. Moreover, preterm infants had a higher rate of pertussis-related hospitalization than full-term infants [IRR = 1.99 (95% CI: 1.47–2.71)]. The VE against reported pertussis for the third dose was 88.8% (95% CI: 84.3–92.0) in full-term infants and 93.0% (95% CI: 85.8–96.5) in preterm infants.

Conclusions:

In this cohort study, preterm infants including those born at GA 35 and 36 weeks had increased risk of reported pertussis. The VE was similar in preterm and full-term infants.

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