Impact of the change to inactivated poliovirus vaccine on the immunizationstatus of young children in the United States: A study from Pediatric Research in Office Settings and the National Medical Association

Objective. To determine whether the change from an all oral poliovirus vacc ine (OPV) schedule to an inactivated poliovirus vaccine (IPV)-containing sc hedule has adversely affected the immunization status of young children in the United States. Methods. Immunization data were abstracted from the medical records of chil dren 8 to 35 months old seen consecutively for any reason in the offices of practicing pediatricians who are members of the Pediatric Research in Offi ce Settings network of the American Academy of Pediatrics or the National M edical Association. Data on up to 120 eligible children were collected in e ach practice between March 1998 and January 2000. Patients were classified as fully immunized at 8 months old if they had received 3 diphtheria-tetanu s-pertussis, 2 Haemophilus influenzae type b, 2 hepatitis B, and 2 poliovir us vaccines. Study children who were greater than or equal to 12 months of age at the time that data were collected were categorized as being fully im munized at 12 months if they had received the same vaccines before their fi rst birthday. To assess the effect of type of poliovirus vaccines on these outcomes, study patients were classified as being in an IPV or OPV group ba sed on the initial type of vaccine received. Logistic regression was used t o calculate the odds ratios (ORs) and 95% confidence intervals (CIs) for IP V as a predictor of being fully immunized at 8 and 12 months of age, after adjusting for race/ethnicity of the patient, maternal education level, year of birth, and method of payment for vaccines. In addition, the effect of c lustering of children within practices was accounted for by the use of gene ralized estimation equation techniques. Results. Data were analyzed on 13 520 children from 177 practices in 42 sta tes; 79.4% of patients were fully immunized at 8 months of age, and 88.7% o f those eligible were fully immunized at 12 months of age. A total of 6910 patients (51.1%) were classified as OPV recipients, wheras 5282 (39.1%) rec eived IPV. In addition, 1328 children (9.8%) were documented as having rece ived poliovirus vaccine, but the particular type could not be determined. C ompared with OPV recipients and after controlling for the confounding varia bles and the effect of clustering within practices, children in the IPV gro up were as likely as were OPV recipients to be fully immunized at 8 months of age (OR: 1.04; 95% CI: 0.88,1.23). At 12 months of age, the OR for IPV a s a predictor of being fully immunized was 1.08 (95% CI: 0.90,1.30). When c ompared with OPV recipients, adjusted ORs for children in the undetermined poliovirus vaccine type group being fully immunized at 8 and 12 months of a ge were 0.84 (95% CI: 0.68,1.04) and 0.84 (95% CI: 0.67,1.07), respectively . Conclusions. The results of this national study indicate that the implement ation of an IPV-containing poliovirus vaccine schedule has not had an adver se effect on the immunization status of young children who were vaccinated in the offices of practicing pediatricians.