Early Childhood Vaccination Status of Preterm Infants

Preterm infants are at increased risk for vaccine-preventable infections and associated complications. Limited studies describe timely vaccination of these vulnerable infants.

This retrospective cohort study included Washington State infants with birth hospitalizations at an urban academic medical center between 2008 and 2013. Demographic, clinical, and visit data from electronic health records were linked to vaccine data from the Washington State Immunization Information System. Completion of the recommended 7-vaccine series by 19 months of age was compared between preterm infants (born at <37 weeks' gestation) and term/postterm infants (born at 37-43 weeks' gestation) by using Pearson's χ² test and multivariable logistic regression. Secondary outcomes included 7-vaccine series completion by 36 months of age and receipt of individual vaccines in the series. Rotavirus, hepatitis A, and influenza vaccination was also assessed.

Of study infants (n = 10 367), 19.3% were born prematurely. Preterm infants had lower 7-vaccine series completion compared with term/postterm infants by 19 months (47.5% vs 54.0%; adjusted odds ratio 0.77 [95% confidence interval 0.65-0.90]) and 36 months (63.6% vs 71.3%; adjusted odds ratio 0.73 [95% confidence interval 0.61-0.87]). Early preterm (23-33 weeks' gestation) and late preterm (34-36 weeks' gestation) infants had a lower rate of 7-vaccine series completion compared with term/postterm infants. Full influenza vaccination coverage by 19 months also differed between groups (early preterm: 47.7%; late preterm: 41.5%; term/postterm: 44.7%; P = .02).

Over half of preterm infants were undervaccinated at 19 months; one-third failed to catch up by 36 months. Strategies to improve vaccination of these high-risk infants are needed.