Antibody persistence and immune memory response following primary vaccination and boosting with live attenuated SA 14-14-2 Japanese encephalitis vaccine (CD-JEV) in Bangladesh: A phase 4 open-label clinical trial

•Despite a lack of measurable antibody four years after primary vaccination, the anamnestic response to a booster dose of live, attenuated SA 14-14-2 Japanese encephalitis vaccine indicates immunity persists.•Live, attenuated SA 14-14-2 Japanese encephalitis vaccine is safe and well-tolerated. Japanese encephalitis (JE) virus is one of the leading causes of viral encephalitis across temperate and tropical zones of Asia. The live attenuated SA 14-14-2 JE vaccine (CD-JEV) is one of three vaccines prequalified by the World Health Organization (WHO) to prevent JE. WHO currently recommends a single CD-JEV dose for infants in endemic settings. However, in the absence of long-term immunogenicity data, WHO has indicated a need for long-term immunogenicity studies to inform optimal dosing schedules and determine the need for booster doses. This Phase 4, open-label clinical study measured neutralizing antibody (NAb) titers in Bangladeshi children three and four years after primary CD-JEV vaccination and 7 and 28 days after a booster CD-JEV vaccination given four years after primary vaccination. The study also assessed the tolerability and safety of the booster dose. A NAb titer of ≥1:10 was considered seroprotective. Of 560 children vaccinated between 10 and 12 months of age with CD-JEV three years earlier and enrolled in this study from 30 July 2015 through 03 January 2016, 52 (9.3%; 95% CI: 7.2–12.0) had a seroprotective titer at enrollment. One year later, of 533 children, 66 (12.4%; 95% CI: 9.9–15.5) had a seroprotective titer before receiving a booster dose. Of 524 children who received a booster CD-JEV dose, 479 (91.4%; 95% CI: 88.7–93.5) and 514 (98.1%; 95% CI: 96.5–99.0) were seroprotected 7 and 28 days later, respectively. The geometric mean titer (GMT) was 6 (95% CI: 6–6) at baseline, 105 (95% CI: 93–119) 7 days post-booster, and 167 (95% CI: 152–183) 28 days post-booster. No vaccine-associated neurologic adverse events or other serious adverse events were noted following the booster dose. Although most children did not have measurable antibody titers three and four years after a single primary CD-JEV dose, more than 90% of seronegative children had a strong anamnestic response within one week of a booster dose. This suggests that these children were immune despite the absence of measurable NAb prior to their booster. ClinicalTrials.gov Identifier: NCT02514746.