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Live attenuated varicella vaccine in healthy 12- to 24-month-old children
C E Johnson1, P A Shurin, D Fattlar
1Department of Pediatrics, Case Western Reserve University School of Medicine, Cleveland Metropolitan General Hospital, OH 44109.
Insights
The Oka/Merck varicella vaccine is safe and effective for children and siblings, showing high immunogenicity and protection against chickenpox exposure. Vaccinated individuals experienced milder cases if infected.
Area of Science:
- Immunology
- Vaccinology
- Pediatrics
Background:
- Varicella (chickenpox) is a common viral infection, particularly in children.
- Live attenuated vaccines are crucial for preventing infectious diseases.
- Assessing vaccine safety and immunogenicity in pediatric populations is essential.
Purpose of the Study:
- To evaluate the safety and immunogenicity of the live attenuated Oka/Merck varicella vaccine.
- To assess the vaccine's efficacy in preventing or mitigating varicella infection in young children and their siblings.
- To determine antibody persistence and response to natural varicella exposure post-vaccination.
Main Methods:
- A study involving 147 children (12-24 months) and 94 older siblings (2-12 years) who were seronegative for varicella.
- Monitoring for vaccine side effects, including rash.
- Assessing seroconversion rates using antibody tests and measuring antibody titers at baseline and follow-up.
- Tracking varicella exposure and disease severity in vaccinated individuals.
Main Results:
- The vaccine demonstrated a favorable safety profile with mild side effects (papular rash in 10.2% of children and 7.4% of siblings).
- High seroconversion rates were observed: 96.6% in children and 94.7% in siblings within six weeks.
- Antibody levels remained detectable in 92.9% of children one year post-vaccination, though geometric mean titers decreased.
- Vaccinated children exposed to varicella experienced milder disease, with only two cases observed in seroconverters.
Conclusions:
- The Oka/Merck varicella vaccine is safe and highly immunogenic in children aged 12 months and older.
- The vaccine provides significant protection against natural varicella exposure, with a 96% reduction in observed cases during the first year.
- Varicella cases occurring in vaccinated individuals are substantially milder in severity.
Abstract:
We studied live attenuated Oka/Merck varicella vaccine in 147 seronegative children 12 to 24 months of age and their 94 seronegative older siblings 2 to 12 years of age. The vaccine side effects were mild, consisting of a papular rash in 15 of 147 (10.2%) children 12 to 24 months and seven of 94 (7.4%) siblings. In a subset of 12- to 24-month-old children, modified fluorescent antibody test for membrane antigen was not detectable at seven days postimmunization but was detectable in 50% by 14 days and in 100% by 21 days. Within 6 weeks, 96.6% of children 12 to 24 months and 94.7% of siblings seroconverted. The geometric mean titer did not vary with age at immunization. One-year blood samples were obtained from 70 children 12 to 24 months of age who seroconverted; 92.9% retained detectable antibody. The geometric mean titer had decreased from 55.7 to 18.6. Of these 70 children, 34% had been exposed to varicella since immunization, and two cases of varicella were observed in seroconverters. Both cases were mild, with less than 50 vesicles. Oka/Merck varicella vaccine appears to be safe, highly immunogenic, and protective against 96% of exposures to natural varicella during the first year after vaccination in infants. Those cases of varicella that develop in immunized children appear substantially reduced in severity.