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Risk factors for breakthrough varicella in healthy children
Insights
Younger children vaccinated against varicella (chickenpox) and those receiving a lower vaccine titre experienced more breakthrough infections. These findings are crucial for optimizing varicella vaccination strategies in children.
Area of Science:
- Immunology
- Vaccinology
- Pediatrics
Background:
- Breakthrough varicella (chickenpox) can occur despite vaccination.
- Understanding risk factors is essential for improving vaccine efficacy and public health strategies.
Purpose of the Study:
- To identify risk factors associated with breakthrough varicella infections in healthy children.
- To evaluate the impact of vaccination age and vaccine titre on varicella vaccine effectiveness.
Main Methods:
- A double-blind randomized controlled trial involving 181 healthy children vaccinated with a reformulated Oka strain varicella vaccine.
- Children received either high or low titre vaccine at ages 9-24 months, with follow-up for breakthrough varicella.
Main Results:
- Household contact with varicella significantly increased the risk of breakthrough infection (OR, 19.89).
- Vaccination at or before 14 months of age (OR, 2.30) and receiving low titre vaccine (OR, 2.13) were identified as risk factors.
- Most breakthrough cases presented with modified varicella illness, particularly in the low-titre vaccine group.
Conclusions:
- Vaccination age of 14 months or younger and low vaccine titre are significant risk factors for breakthrough varicella.
- These findings have important implications for the optimal implementation of varicella vaccination programs in pediatric populations.
Aim:
To evaluate the risk factors for breakthrough varicella in a follow up study of a cohort of 181 healthy children immunised when aged 9-24 months with a reformulated Oka strain varicella vaccine (SmithKline Beecham Biologicals/Oka).
Design:
The children were randomised in a double blind manner into one of four groups to receive one of two production lot vaccine batches, at two different titres (high titre, 10(3.9) and 10(4.0) plaque forming units (pfu); low titre (heat exposed), 10(2.7) and 10(2.8) pfu). The overall seroconversion rate after immunisation was 99%.
Results:
One hundred and sixty-eight patients were available for review after a mean (SD) follow up of 35 (9) months after vaccination. Multivariate analysis indicated that risk factors for breakthrough varicella were household contact with varicella (adjusted odds ratio (OR), 19.89; 95% confidence interval (CI), 18.39 to 21.39), vaccination age of < or = 14 months (adjusted OR, 2.30; 95% CI, 1.69 to 2.90), and receiving low titre (10(2.7) pfu) vaccine (adjusted OR, 2.13; 95% CI, 1.54 to 2.73). All children who developed breakthrough varicella, had a modified varicella illness, except for three, all of whom had received low titre vaccine.
Conclusion:
The identification of young immunisation age (< or = 14 months) and low titre vaccine as risk factors for breakthrough varicella have important implications for the implementation of varicella vaccination programmes in healthy children.