BACKGROUND:
Surveillance for a disease is needed to facilitate public health action at the state and local level and to monitor the impact of various immunization programs. In order to establish Pennsylvania's baseline data on varicella morbidity as well as incidence by age group, sentinel surveillance on varicella disease was established throughout the State beginnning in January 1999.

OBJECTIVE:
1) To gather information of baseline and on going incidence, morbidity and mortality of the varicella disease,
2) To collect valid medical information about the reported varicella illness and immunization(s) received, and
3) To evaluate the effectiveness of current varicella vaccination strategies.

METHOD:
Active surveillance is conducted weekly in 67 counties. The sentinel sites are concentrated in populated areas; emphasis is placed on elementary schools, daycare centers, and physician offices, especially pediatricians. Reports of aggregated numbers of cases are counted by age group. Each county reports to the Division of Immunizations the last Friday of every month.

RESULT:
There are 1070 sentinel surveillance sites across the State. The findings in the four years of surveillance data show the total aggregated case count are markedly lower (28%) in 2002 (3642) than in 1999 (5058). The increasing level (18.8%) of varicella coverage rates in PA from 57.5% in 1999 to 76.5% in 2001 also substantiated the determination that varicella vaccine has impacted in changing the varicella disease incidence in the state.

CONCLUSION:
This data has demonstrated that the decline of disease count over the years is due to the ipact of vaccine usage.

LEARNING OBJECTIVES:
How to effectively assess the incidence of varicella and monitor impact of vaccination program.