Related Experiment Videos
Younger age at vaccination may increase risk of varicella vaccine failure
Karin Galil1, Elizabeth Fair, Norine Mountcastle
1Centers for Disease Control and Prevention, Atlanta, GA 30333, USA. kgalil@cdc.gov
Insights
A varicella outbreak in a highly vaccinated daycare demonstrated vaccine effectiveness (VE) of 79%. However, early vaccination age (<14 months) was linked to increased risk of vaccine failure, suggesting potential for breakthrough varicella disease.
Area of Science:
- Pediatric Infectious Diseases
- Vaccinology
- Epidemiology
Background:
- High varicella vaccination coverage is crucial for community immunity.
- Day-care centers are environments where varicella outbreaks can occur.
- Understanding vaccine effectiveness (VE) in real-world settings is essential.
Purpose of the Study:
- To investigate vaccine effectiveness against varicella during an outbreak in a highly vaccinated population.
- To identify factors associated with breakthrough varicella infections.
Main Methods:
- A cohort study was conducted during a varicella outbreak at a Pennsylvania day-care center (DCC).
- Parental questionnaires collected data on varicella history, vaccination status, and recent illnesses.
- Vaccine effectiveness was calculated for children aged >=12 months without prior varicella disease.
Main Results:
- The outbreak involved 41 cases of varicella among 131 DCC attendees.
- Vaccine effectiveness was 79% against all varicella and 95% against moderate to severe disease.
- Vaccination at less than 14 months of age was associated with a 3-fold increased risk of breakthrough varicella.
Conclusions:
- Despite high vaccination coverage (80%), a significant varicella outbreak occurred.
- Early age at vaccination (<14 months) may be a risk factor for vaccine failure.
- Further research is needed to optimize varicella vaccination schedules.
Abstract:
To determine vaccine effectiveness (VE), a varicella outbreak in a highly vaccinated day-care center (DCC) population in Pennsylvania was investigated. In Pennsylvania, proof of immunity is required for children >or=12 months old for DCC enrollment. Questionnaires were administered to parents of children who had attended the DCC continuously during the study period (1 November 1999-9 April 2000) to determine history of varicella disease or vaccination and for information about any recent rash illnesses. VE was calculated for children >or=12 months old without a history of varicella. There were 41 cases of varicella among 131 attendees, with 14 cases (34%) among vaccinated children. VE was 79% against all varicella and 95% against moderate or severe varicella. Vaccination at <14 months was associated with an increased risk of breakthrough disease (relative risk, 3.0; 95% confidence interval, 0.9-9.9). Despite varicella vaccination coverage of 80%, a sizeable outbreak occurred. Early age at vaccination may increase the risk of vaccine failure.