Background: While the 1-dose varicella vaccination (VV) program effectively reduced varicella disease, hospitalizations, and deaths, school outbreaks continued to occur. In June 2006, the Advisory Committee on Immunization Practices recommended implementation of a routine 2-dose VV program (Dose 1: 12–15 months, Dose 2: 4–6 years).
Objectives: To describe adoption of 2-dose VV and varicella incidence in West Philadelphia (WP) following its implementation.
Methods: Since 1995, the Varicella Active Surveillance Project (VASP) has maintained a network of sites in WP that actively report varicella cases. Between 2003 and 2007, participating healthcare providers also reported individual VV doses administered to their patients. VV administration data for 2008 and 2-dose VV coverage estimates were obtained from Philadelphia’s immunization registry. We calculated varicella incidence rates and used Poisson regression to compare incidence in 2007 and 2008 to the average incidence between 2003 and 2006.
Results: Following the 2-dose recommendation, WP healthcare providers administered 19,044 VV doses in 2007 and 15,811 in 2008, which was 3–4 times higher than the average 5,088 doses administered annually between 2003 and 2006. Among children aged 5–9 years from WP, 2-dose VV coverage reached 30% in 2007 and increased to 51% in 2008. Compared with the average varicella incidence between 2003 and 2006 (39 cases per 100,000 population), rates in 2007 and 2008 declined 11% (35 cases per 100,000 population, P=.30) and 28% (29 cases per 100,000 population, P = .01), respectively. While varicella morbidity among children aged 5–9 years did not decline in 2007, incidence in 2008 was 43% lower than the average incidence for this age group between 2003 and 2006 (91 vs. 160 cases per 100,000 population, P=.03).
Conclusions: The reductions in varicella incidence that occurred in West Philadelphia during 2008 may be evidence of the initial impact of the 2-dose VV regimen.