Abstract
Immunization was first practiced in Thailand in 1977 through the National Expanded Program
on Immunization (EPI) with the aim of significantly reducing morbidity and mortality from common
vaccine-preventable diseases. When first introduced the EPI program coverage level was very low:
about 10-20 percent for many diseases. By 2000 vaccine coverage for nearly all vaccines in the EPI
program was more than 90 percent. Consequently, rates of vaccine preventable diseases (such as
diphtheria, measles, and rubella) in Thailand are very low.
Despite high vaccine coverage in Thailand, however, there has been a resurgence of some
vaccine-preventable diseases. For example, there was a resurgence of diphtheria in eight provinces in
2012, and measles outbreaks occur among children every 3-4 years. There are a few possible
explanations for the return of vaccine-preventable diseases in Thailand. The first possible reason is
population movement, in particular migration to Thailand. Next is low immunization coverage (below
the critical threshold) in particular locations among children aged less than five years old. The other
possible reason for the resurgence is waning immunity in adults. An evaluation of these possible
reasons for the resurgences would help us to identify effective measures to protect against a return of
vaccine preventable diseases in Thailand.
During the period (2012) of the diphtheria outbreak, Bueng-Kan which is located at the border
between Thailand and the Lao People's Democratic Republic, there was an outbreak of hepatitis A
with a case rate of 355 per 100,000. Investigation of this outbreak suggested that contaminated water
and ice were sources of infection. During the past decade Thailand has faced several major
outbreaks of hepatitis A, which resulted in thousands of infected people and hundreds of
hospitalizations. Currently, the hepatitis vaccine is not included in the EPI program.
There are more than 3.5 million persons without Thai nationality living in the country,
including many long-term residents and children of migrants born in Thailand. The approximately 3.1
million migrants working in Thailand comprise about 8 per cent of the labour force. Because of
Thailand’s relative economic and social stability, it is a primary destination for many regional worker
migrants. Those migrants are vulnerable to health risks due to limited or inadequate access to basic
health services and poor living conditions. However, there is little or no data on the immunization
coverage of this group as well as on their movement inside Thailand.The resurgence of vaccine preventable diseases in some parts in Thailand raises the
following questions. What are the reasons for these resurgences? Will the epidemics of these
diseases expand to others part of Thailand? How can they be controlled? Is Thailand sufficiently
protected against a return of vaccine preventable diseases such as diphtheria, measles, rubella, and
hepatitis A?
In order to gain insights into the resurgence of vaccine preventable diseases in Thailand, this
project propose to: 1) explore the epidemiology and dynamics of the resurgence of vaccine
preventable disease epidemics in Thailand; 2) determine the seroprevalence of vaccine preventable
diseases among migrant populations in Thailand; 3) determine contact and movement patterns of
migrant populations in Thailand; 4) use mathematical models to demonstrate possible scenarios for
the spread of vaccine preventable diseases among migrants and Thai nationals taking into account
the effect of population movement patterns and to suggest optimal control strategies; 5) use
mathematical models to evaluate the spatial dimension of vaccine preventable disease spread among
migrants and the Thai population; and 6) determine the cost-effectiveness of implementing vaccination
campaigns for the migrant population in Thailand. The end result of the whole project will be an
evidence base which can be practically used by the public health sector for epidemic mitigation,
prevention and control.
