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Chickenpox outbreak in a highly vaccinated school population
Barna D Tugwell1, Lore E Lee, Hilary Gillette
1Epidemic Intelligence Service, Epidemiology Program Office, Centers for Disease Control and Prevention, Atlanta, Georgia, USA.
Pediatrics
|March 3, 2004
Summary
A chickenpox outbreak occurred despite high vaccination rates. Breakthrough disease was more common in students vaccinated over five years prior, suggesting a need for booster shots.
Area of Science:
- Epidemiology
- Vaccinology
Background:
- Public schools implemented varicella vaccination requirements in 2001.
- Chickenpox (varicella) outbreaks can occur even in highly vaccinated populations.
Purpose of the Study:
- To investigate a chickenpox outbreak in an Oregon elementary school.
- To determine varicella vaccination rates, vaccine effectiveness, and risk factors for breakthrough disease.
Main Methods:
- Case definition: acute maculopapulovesicular rash without other explanation in a student without prior chickenpox history.
- Data collection: varicella vaccination records and prior chickenpox history.
- Analysis: calculation of vaccine effectiveness and evaluation of risk factors for breakthrough disease.
Main Results:
- Of 422 students, 218 had no prior chickenpox, and 97% were vaccinated.
- Vaccine effectiveness was 72% (95% CI: 3%-87%).
- Students vaccinated >5 years prior were 6.7 times more likely to develop breakthrough disease than those vaccinated ≤5 years prior.
Conclusions:
- A chickenpox outbreak occurred in a school with high vaccination coverage.
- Longer intervals since vaccination (>5 years) were associated with increased risk of breakthrough varicella.
- Booster vaccination for chickenpox warrants further consideration.