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Japanese encephalitis vaccination yields high protection rates in at-risk toddlers
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Live-attenuated Japanese encephalitis vaccine provided seroprotection for up to 5 years against Japanese encephalitis wild-type virus after vaccination and 96% to 98% protection against genotype III strains, according to recently published data.
“Recent analyses of circulating strains have shown a shift from genotype III in favor of genotype I in Vietnam and Thailand, suggesting that a genotype shift phenomenon may be occurring throughout Southeast Asia,” Emmanuel Feroldi, MD, from the department of clinical development at Sanofi Pasteur, and colleagues wrote. “There is no indication yet that this shift towards genotype I is affecting the efficacy of the [Japanese encephalitis (JE)] vaccines in use, which are all derived from genotype III viruses (strains Nakayama, P3, Beijing-1 and SA14-14-2), although some studies have shown differences in the capability of the sera of vaccinees who received genotype III to neutralize in vitro [wild-type (WT)] strains from non-vaccine strains, namely genotype I isolates.”
To assess whether responses at distal time points after JE vaccination caused WT isolate neutralization, Feroldi and colleagues analyzed serum samples from 47 children aged between 2 years and 5 years who underwent JE booster vaccination (JE-CV, Imojev) following an inactivated JE vaccine immunization. The researchers measured antibody titers at baseline using a panel of WT JE strains and post-vaccination at 28 days, 6 months and 5 years.
Serum analysis showed that 43 (91.5%) of the children vaccinated with JE-CV booster had neutralizing antibody titers of 10 or more (1/dilue) against the homologous strain prior to vaccination and maintained protection from JE WT at 5 years. Seroprotection at baseline was between 78.7% and 87.2% and all children were protected against genotype IV WT at 28 days and 6 months. Researchers observed the greatest protection at 5 years against viral strain genotype III Beijing (immunogenicity value, 181.3; 95% CI, 124-264.9) and the lowest protection against genotype IV JKT 9092/TVP 6265 (immunogenicity value, 69.5; 95% CI, 51.7-99.3).
“The sera drawn from JE-CV vaccinees 28 days, 6 months and 5 years’ post-vaccination are able to neutralize WT viruses of the four main genotypes circulating in Southeast Asia and in India where JE is endemic,” the researchers wrote. “Our data are useful for decision making on JE vaccination strategy, keeping in mind that a shift from genotype III strains to genotype I strains has been increasingly observed in some Asian countries.” – by Kate Sherrer
Disclosure: This study was funded by Sanofi Pasteur. Feroldi is an employee of Sanofi Pasteur. Please see the full study for a list of all other researchers’ relevant financial disclosures.
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