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Clinical experience with Oka live varicella vaccine in Japan
Insights
The Oka strain live varicella vaccine is safe and effective for children, including those with high-risk conditions like leukemia. This vaccine provides solid immunity against varicella and zoster, with fewer reactions when chemotherapy is paused.
Area of Science:
- Immunology
- Pediatrics
- Vaccinology
Background:
- Live varicella vaccine (Oka strain) has been available since 1974.
- Vaccination is recommended for high-risk children, including those with acute leukemia, during remission and with modified chemotherapy protocols.
Purpose of the Study:
- To evaluate the safety and efficacy of the Oka strain live varicella vaccine in children.
- To assess immune response and clinical reactions in children with acute leukemia and other conditions.
Main Methods:
- Vaccination of children with acute leukemia in remission, with temporary suspension of chemotherapy.
- Comparison of clinical reactions and immune responses between vaccinated groups with and without chemotherapy suspension.
- Assessment of vaccine efficacy through follow-up studies and comparison with natural varicella infection.
Main Results:
- Lower incidence of clinical reactions (15.2%) when chemotherapy was suspended compared to when it was not (41.7%).
- Most vaccinees showed an immune response; 11% experienced varicella after natural exposure due to immunosuppression.
- Vaccinated children had reduced incidence and severity of zoster compared to natural infection.
- Approximately 1,500 children with nonmalignant diseases and 4,000 healthy children showed satisfactory immune responses with few reactions.
- A 7-10 year follow-up confirmed solid immunity conferred by the vaccine.
Conclusions:
- The Oka strain live varicella vaccine is effective in preventing varicella in both high-risk and normal children.
- Vaccination is beneficial for children with acute leukemia, especially when administered during remission with appropriate chemotherapy management.
- The vaccine demonstrates a favorable safety profile and provides long-lasting protection against varicella and zoster.
Abstract:
A live varicella vaccine (Oka strain) has been developed and used since 1974 in normal and diseased children, particularly those at high risk. Children with acute leukaemia were usually vaccinated while in remission when showing a normal cell-mediated immunity as assessed with phytohaemagglutinin (PHA) or other reagents, and during suspension of all anticancer therapy, except 6-mercaptopurine from 1 week before to 1 week after vaccination. While clinical reactions were observed in only 40 out of 263 (15.2%) of these patients, they were noted in 30 out of 72 (41.7%) children immunized without suspension of chemotherapy. Symptoms were mostly mild; only a few cases of the latter group with T-cell leukaemia or malignant lymphoma developed severe symptoms. An immune response was observed in most vaccinees, but some (11%) developed clinical symptoms after exposure to natural varicella due to immunodepression caused by continuing anticancer chemotherapy. In these cases, revaccination seems advisable. The incidence and severity of zoster in vaccinated acute leukaemic children were less than in those with natural infection. Satisfactory immune responses with few concomitant clinical reactions were observed in approximately 1,500 vaccinees having nonmalignant diseases and in about 4,000 normal children. A 7-10-year follow-up study revealed that the vaccine had conferred solid immunity on the children. These results indicate that live varicella vaccine of the Oka strain is useful in preventing varicella in high-risk as well as in normal children.