BACKGROUND:
Varicella is a highly communicable disease caused by the varicella zoster virus. Approximately 1% of vaccinees develop breakthrough infection each year. Breakthrough varicella (BV) is defined as the occurrence of varicella among vaccine recipients. Breakthrough infection is significantly milder with fewer lesions (generally <50), many of which are maculopapular instead of vesicular. BV may be indicative of loss of potency of the vaccine or improper storage and handling. Varicella vaccine (Varivax ) is the vaccine used and it has to be stored strictly at temperature conditions of 50F or lower.

OBJECTIVE:
To analyze BV in a county in upstate New York.

METHOD:
Vaccine failure forms sent to the New York State Department of Health (NYSDOH) Immunization Program were analyzed and entered into an MS-Excel spreadsheet (32 in total). Eleven variables were analyzed including the following: Age At vaccination, total number of lesions (very few, <50, 50-200, >200), and date of rash onset, among others.

RESULT:
The results included the following:
1. Of the 32 children, 19 (62%) had less than 50 lesions, 11 (35%) had 50-200 lesions and 1 (3%) had greater than 200 lesions.
2. The time from vaccination to rash illness onset ranged from 0.2 months-92.9 months with a median of 68.13 months. The number of cases increased as the time between vaccination and rash onset increased.

CONCLUSION:
1. The number of BV cases increased as the time period between vaccination and date of rash onset grew longer
2. 35% of the children had 50-200 lesions and 3% had >200 lesions.
3. Both may be indicative of waning of the immunity provided by the vaccine.

LEARNING OBJECTIVES:
1. This was a pilot analysis and gives general information on factors that influence BV.
2. This study indicates that BV is an occurrence of concern to public health professionals.