Estimates of the global burden of Japanese encephalitis and the impact of vaccination from 2000-2015

Abstract

Japanese encephalitis (JE) is a mosquito-borne disease, known for its high mortality and disability rate among symptomatic cases. Many effective vaccines are available for JE, and the use of a recently developed and inexpensive vaccine, SA 14-14-2, has been increasing over the recent years particularly with Gavi support. Estimates of the local burden and the past impact of vaccination are therefore increasingly needed, but difficult due to the limitations of JE surveillance. In this study, we implemented a mathematical modelling method (catalytic model) combined with age-stratifed case data from our systematic review which can overcome some of these limitations. We estimate in 2015 JEV infections caused 100,308 JE cases (95% CI: 61,720–157,522) and 25,125 deaths (95% CI: 14,550–46,031) globally, and that between 2000 and 2015 307,774 JE cases (95% CI: 167,442–509,583) were averted due to vaccination globally. Our results highlight areas that could have the greatest benefit from starting vaccination or from scaling up existing programs and will be of use to support local and international policymakers in making vaccine allocation decisions.

The current burden of Japanese encephalitis and the estimated impacts of vaccination: Combining estimates of the spatial distribution and transmission intensity of a zoonotic pathogen

“…A recent study by Quan et al [20] estimated that there were over 100,000 (95% CI: 61,720-157,522) JE cases in 2015, an estimate over 50% higher than our estimate (although there is overlap in the 95% confidence intervals of the two estimates). Quan et al [20] used a similar method of first estimating the FOI in each country based on age-specific case data obtained from a systematic review.…”

“…This combination of high FOIs (in some countries) and a larger at-risk population leads to the higher incidence estimates of Quan et al [20] relative to our estimates and those of Campbell et al [1]. As a result, for several countries, such as Bangladesh and Pakistan, where we estimate that the at-risk population is a fairly large percentage of the population in the "endemic" region of the country, our incidence estimates are similar to the estimates of Quan et al [20]. For several countries-including Laos, Malaysia, Myanmar, Philippines, and Thailand-the incidence estimates of Quan et al [20] are two to four times higher than our estimates due to our lower estimates of the sizes of the at-risk populations.…”

“…These country-specific FOI estimates were then used to estimate incidence in each country using the regional classifications and endemic population sizes from Campbell et al [1]. This combination of high FOIs (in some countries) and a larger at-risk population leads to the higher incidence estimates of Quan et al [20] relative to our estimates and those of Campbell et al [1]. As a result, for several countries, such as Bangladesh and Pakistan, where we estimate that the at-risk population is a fairly large percentage of the population in the "endemic" region of the country, our incidence estimates are similar to the estimates of Quan et al [20].…”

“…We used a non-negative, truncated N ormal(0, 10) prior for λ. To incorporate sufficient uncertainty in the priors for the vaccination coverage parameters, υ a,t , we used an informative prior υ a,t ∼ Beta(φ(1 −υ a,t ), φυ a,t ) following the approach detailed by Quan et al [20]. The valueυ a,t was the initial estimate of the vaccination coverage in age class a derived from reported vaccination coverage levels at the national level (see SI Table 1 for data sources).…”

Prioritised Zoonotic Diseases of Nepal: A Review

“…JE virus is the main cause of viral encephalitis in many countries of Asia with an estimated 68,000 clinical cases, and around 13,600 to 20,400 people die of this disease every year. More than 20countries in South-East Asia and Western Pacific regions have JEV transmission risk exposing more than 3 billion people to risks of infection (Quan et al, 2020).The very first case of this disease in Nepal was identified in 1978. 1,823 human cases of Japanese encephalitis was found in Nepal from 2007-2015 which suggests that it is a reoccurring zoonotic disease which exists in the endemic form (Pant et al, 2017).…”