Continuing Decline in Varicella Incidence After the 2-Dose Vaccination Recommendation-Connecticut, 2009-2014

Background.  Varicella is a highly contagious vaccine-preventable illness. In 1996, the Advisory Committee for Immunization Practices recommended 1 dose of vaccine for children, and in 2006 it recommended 2 doses; Connecticut required 1 dose for school entry in 2000 and 2 doses for school entry starting in 2011. Connecticut varicella incidence overall and among persons aged 1-14 years declined during 2005-2008. We analyzed varicella surveillance data for 2009-2014 to characterize overall and age group-specific trends in the setting of the 2-dose requirement. Methods.  Passive surveillance was used to collect data and identify incidence trends and changes in proportions, and these were assessed by χ(2) tests for trend and proportion, respectively. Results.  Varicella incidence decreased from 13.8 cases/100 000 persons during 2009 to 5.1 cases/100 000 persons during 2014 (P < .001); significant declines in incidence occurred among children aged 1-4, 5-9, and 10-14 years (P < .01 for each age group). Cases classified as preventable decreased from 44% during 2009 to 25% during 2014 (P < .01); significant declines in percentages of preventable cases occurred only among those aged 5-9 years (P < .05) and 10-14 (P < .01) years. Conclusions.  Varicella incidence continued to decline in Connecticut in the setting of the 2-dose school-entry program. Continued surveillance is needed to assess the full influence of the 2-dose recommendation.