Geographic Clusters of Underimmunization

Deborah Lehman, MD reviewing Lieu TA et al. Pediatrics 2015 Feb.

Areas with high rates of underimmunized children overlap with areas where families refuse vaccines.

Control and eradication of vaccine-preventable diseases rely on high levels of vaccination. For some infections, such as measles, this level needs to be above 95% to achieve herd immunity and protect children too young to be immunized. Recent studies have demonstrated that disease outbreaks overlap geographically with areas where parents refuse vaccines (NEJM JW Pediatr Adolesc Med Jun 26 2013).

Researchers examined health records from Kaiser Permanente of Northern California for more than 150,000 children born between 2000 and 2009 and followed until at least age 36 months. From 2002 to 2012, rates of underimmunization (child missed at least 1 recommended vaccine by age 36 months) increased annually by an average of 6%, peaking at 13% in 2010. Asians and Hispanics and children with higher family income were less likely to be underimmunized, whereas those with higher household education level were more likely to be underimmunized. Analysis of records for 2010 to 2012 identified five statistically significant geographic clusters of underimmunization in which underimmunization rates ranged from 18% to 23%, compared with 11% outside the clusters. Families in the clusters, compared with those outside the clusters, were more likely to be white, shot limiters (child did not receive more than 2 injections at a single visit before age 36 months), and documented vaccine refusers.

Citation(s):

Lieu TA et al. Geographic clusters in underimmunization and vaccine refusal. Pediatrics 2015 Feb; 135:280.