Control of infectious diseases in Asia

Abstract

Recent outbreaks of newly emerged pathogens such as the Middle East respiratory syndrome (MERS-CoV) have been a wake-up call for a global health society, alarming the importance of continuous and collaborative efforts to combat infectious diseases. Vaccination and early detection followed by timely response to outbreaks are among the most effective means to prevent and control the spread of infectious diseases.

In this study, I examined the epidemiological burden of infectious diseases in Asia with a focus on vaccine-preventable diseases (VPDs) and explored different ways to measure the burden using statistical, mathematical, and economic analyses. Specifically, I aimed to examine historical trends of notifiable infectious diseases and to assess the impact of the expanded immunization program on the burden of VPDs in China; to estimate influenza-associated excess mortality and to examine patterns in excess mortality by age, influenza type/subtype, and geographic area in Korea; to conduct an epidemiological assessment of the MERS-CoV outbreak in Korea to describe and update key epidemiological determinants of MERS-CoV outbreaks; and to examine the effect and implications of different approaches to monetize benefits on public health decision-makings by using the HPV vaccination as the case study.

I used the dataset on nationally notifiable diseases collected by China CDC to conduct descriptive analyses and estimate the impact of the immunization program using quasi-Poisson regression models. There were significant reductions in the incidence (95%) of notifiable diseases between 1950 and 2013. The burden of most VPDs have substantially declined (range: 55%-83%) since the respective vaccines were incorporated into the national immunization program. I estimated influenza-associated excess mortality in Korea based on multiple linear regression models with weekly mortality rates stratified by age, region, and cause of death against weekly surveillance data. Influenza was associated with 2,900 annual excess deaths or 1.5% of all deaths in 2003-2013. The burden of influenza was substantial particularly among older and rural populations, with largely varying estimates by age, regions, and seasons. Using the epidemiological data on the MERS-CoV outbreak collected from Korea CDC and WHO, I estimated that the mean incubation period was 6.7 days and the mean serial interval was 12.6 days, while the case fatality risk (CFR) was 21.3% (CrI: 13.8%, 31.0%). By the end of the outbreak, 186 cases including 36 deaths were reported, yielding the CFR of 19.4%, which is close to my estimate. Next, I conducted cost-benefit analysis (CBA) using eight conventional and integrated methods in to monetize benefits of HPV vaccination in the UK. The estimated benefits varied by more than 20-fold (£0.6-12.4 billion) across the approaches with the threshold vaccine cost estimates ranging over an order of magnitude (£69–£1,417).

My findings show that vaccination substantially reduces the epidemiological and economic burden of infectious diseases. Strengthening the disease surveillance system while developing a rapid response manual is crucial to reduce the risk of potential superspreading events in future infectious disease outbreaks. Wider use of CBA would require greater convergence in the methods used for monetizing benefits to ensure consistency and comparability across studies.