Epidemiology of Japanese Encephalitis in the Philippines prior to routine immunization.

BACKGROUND

In 2015, we published our findings highlighting the endemicity of Japanese encephalitis (JE) in the Philippines. The policymakers responded by conducting an immunization campaign and strengthening the surveillance system. Using the data on the revitalized surveillance system, we updated the epidemiology of JE in the country METHODS: Electronic databases were searched, and conference proceedings related to JE in the Philippines were identified until 31 December 2018. We used surveillance data from 1 January 2014 to 31 December 2017. We used the 2015 population census to estimate the national and regional incidence for children <15 years old.

RESULTS

Four studies reported on the seroprevalence of JE in the Philippines, which showed increasing seroprevalence with increasing age. Seroprevalence rates were from zero for infants (<1 year old) to 65.7% in adolescents (12-18 years old) before the immunization campaign. Among five studies on clinical profile JE, case fatality ranged from zero to 21.1%, and neurologic sequelae ranged from 5.2% to 81.8% of diagnosed cases. In the surveillance data, JE cases peaked annually from July to October, coinciding with the wet season. The national incidence was estimated at 0.7 JE cases/100,000 among children <15 years at a minimum, but higher rates were seen in the northern regions of the country.

CONCLUSION

Improved surveillance affirmed the burden of JE in the Philippines. A subnational immunization campaign in April 2019 was conducted in the northern regions of the country. We highlight the importance of the inclusion of JE vaccine in the immunization program and sustained high-quality surveillance to monitor its impact on JE control.