Long-Term Immune Response With Single-Dose, Inactivated Japanese Encephalitis Vaccine

An inactivated, single-dose vaccine for Japanese encephalitis (JENVAC^®, India) had the highest geometric mean titer (GMT) response and long-term persistence of neutralizing antibodies compared with a live, attenuated vaccine (SA 14-14-2, China) in healthy children aged 1 to 15 years, according to study results published in The Journal of Infectious Diseases.

JENVAC is a Vero cell-derived vaccine prepared from an Indian strain (Kolar-821564XY). Study authors conducted a phase-4, open-label, randomized, controlled trial at 4 sites in India to evaluate and compare the interchangeability of a 2-dose regimen of either vaccine and the immunogenicity and safety of single-dose JENVAC with SA 14-14-2 vaccine.

Children were randomly assigned in a 1:1 ratio to receive JENVAC (n=180) or SA 14-14-2 (n=179) on day 0 and were followed until 1 year after receipt of a single dose of either vaccine. Each group was stratified into 3 age-wise subgroups: children aged 1-5 years, 6-10 years, and 11-15 years. On day 720, 178 children received a booster of either the vaccination previously received or were interchanged to receive the alternative vaccine, leading to 4 treatment arms: JENVAC + JENVAC (n=46), JENVAC + SA 14-14-2 (n=50), SA 14-14-2 + JENVAC (n=46), and SA 14-14-2 + SA 14-14-2 (n=36).

The 50% plaque reduction neutralization titer (PRNT₅₀) values were transformed to seroprotection (proportion of children with a PRNT₅₀ ≥10 U/mL), seroconversion (PRNT₅₀ of ≥10 U/mL if the baseline titer was <10 U/mL or as a 4-fold increase if the baseline titer was ≥10 U/mL), and GMTs.

There were no significant demographic and baseline differences between the JENVAC and SA 14-14-2 groups. At day 360, GMTs were 33.7 (95% CI, 27.9-40.77) in the JENVAC group and 12.2 (95% CI, 10.3-14.4) in the SA 14-14-2 group. Seroprotection was achieved by 81.7% (95% CI, 74.9-87.3%) in the JENVAC group and 47.9% (95% CI, 40.1-55.8%) in the SA 14-14-2 group.

JENVAC reported statistically higher immune responses at day 28 and subsequent time points. In the JENVAC-stratified age groups, the seroprotection at day 360 was 85.7% (95% CI, 76.6-94.9%), 75.9% (95% CI, 64.5-87.3%), and 83.3% (95% CI, 73.4-93.3%) in children aged 1-5 years, 6-10 years, and 11-15 years, respectively.

At day 720, 88.5% (95% CI, 80.4-94.1%) in the JENVAC group and 68.3% (995% CI, 57.1-78.1) in the SA 14-14-2 group achieved seroprotection. The estimated GMT ratio for recipients of JENVAC at the first dose, relative to the GMT for recipients of SA 14-14-2 at the first dose, was 2.91 (P <.0001). At day 748, the group that received JENVAC + JENVAC had the highest GMT response.

“A single-dose [of Japanese encephalitis] vaccine may be advantageous for mass vaccination. Further boosting at later time points may be beneficial,” study authors concluded.

Disclosure: Several study authors declared affiliations with the pharmaceutical industry. Please see the original reference for a full list of authors’ disclosures.