Frequency of alternative immunization schedule use in a metropolitan area

Recent studies have described an increase in parental hesitancy regarding vaccines as well as increases in parental adoption of vaccine schedules that delay or limit receipt of recommended vaccines. This study quantifies potential prevalence and trends in alternative schedule compliance by measuring consistent shot-limiting in a metropolitan area of Oregon.

Retrospective cohort analysis using the Oregon ALERT Immunization Information System to track children born between 2003 and 2009 in the Portland metropolitan area. Joinpoint regression was used to analyze prevalence trends in consistent shot-limiting during that time period. The 2007-2009 Haemophilus influenzae type b vaccine shortage and increased availability of combination vaccines were also examined for their effects on shot-limiting rates.

A total of 4502 of 97,711 (4.6%) children met the definition of consistent shot-limiters. The proportion of consistent shot-limiters in the population increased from 2.5% to 9.5% between 2006 and 2009. Compared with those with no or episodic limiting, consistent shot-limiters by 9 months of age had fewer injections (6.4 vs 10.4) but more visits when immunizations were administered (4.2 vs 3.3). However, only a small minority of shot-limiters closely adhered to published alternative schedules.

The percentage of children consistently receiving 2 or fewer vaccine injections per visit between birth and age 9 months increased threefold within a 2-year period, suggesting an increase in acceptance of non-Advisory Committee on Immunization Practices vaccine schedules in this geographic area.