Travel medicine evolved as an interdisciplinary field in the late 1980s with an initial focus on travelers from Europe, North America, Australia, and New Zealand (referred to as “Western” countries) visiting developing countries. The basis of travel medicine was to try to decrease the risks of disease and injury for individual travelers when visiting environments perceived as having excess health risks compared to the home country.
Owing to economic growth in large parts of Asia, the number of outbound travelers from this region is dramatically increasing. In 1990, only 50 million Asians traveled abroad, while this number reached 100 million in the year 2000 and 190 million in 2010. The outbound tourism growth rate among Asian travelers is the highest in the world. Thus, travelers from Asia are becoming a major proportion of world tourism. In 1980 less than 10% of international travelers were from Asia. This proportion doubled in 2010 and it is expected to reach 30% in 2030, equal to 500 million.
So far, the concept of travel medicine is not well known in Asia among both travelers and health care professionals. Only 21% to 40% of Asian travelers sought pre-travel health information before their trip;[2-4] this proportion being far lower as compared to 60% to 80% in “Western” travelers.[5, 6] Recent evidence is even more concerning; only 4% of Chinese travelers who traveled to high malaria risk areas visited a travel clinic before their trip, and only 5% of Japanese travelers who traveled to developing countries received hepatitis A vaccine. These rates were far lower than among European travelers.
Using the clinic directory of the International Society of Travel Medicine (ISTM) as a crude indicator, very few travel medicine services have been established in Asia. While one travel clinic in North America serves 220,000 people, in Asia it may have to serve up to 45 million people. It should be noted that the European data are partly misleading, as many countries have highly developed national travel health associations and thus few travel clinic staff apply for membership in ISTM. However, this does not apply to North America, Australia, or Asia.
There may be several reasons for the apparent lack of awareness and interest of travelers or health professionals in regard to travel health risks in Asia:
- The perception of risk. Pre-travel medicine in “Western” countries is mainly focused on diseases that may have become rare, have been eradicated or never existed in their home countries, but remain endemic in large parts of Asia, such as malaria, typhoid, hepatitis A, hepatitis B, dengue, rabies, and Japanese encephalitis (JE). Doctors and travelers from Asia who are familiar with these diseases usually consider that there is no additional risk for these diseases when traveling within Asia. It is a perfectly reasonable assumption that if there is no excess risk between the home country and the destination—considering behavior, lodging, and food choices—no specific protective measures are sought or indicated for the traveler, but a question remains, whether this is equal or more as compared to staying in the home country. Although up to 80% of outbound travelers from Asia travel regionally within Asia, it is important to note that the risk of specific diseases is not the same in all regions of Asia. For instance in Singapore, JE is extremely rare, and thus neither is this vaccine included in their expanded program of immunization (EPI), nor is it recommended to travelers from abroad. On the other hand, when Singaporeans plan to travel elsewhere in Asia, especially to rural areas, they should be informed about the risk and the options of prevention of JE.
- Some “travel vaccines” are already included in Asian country EPI programs. Thus, in contrast to “Western” travelers, travelers from Thailand, China, South Korea, Japan, and parts of India may already be immunized against JE (Table 1). JE boosters are not usually given after a primary vaccination. However, we should not totally rely on the country's EPI schedule as its coverage never reaches 100%. In some particular countries such as India or the Lao People's Democratic Republic, up to 25% of the populations have not been completely immunized according to their EPI (Table 1). This means that in Asia a detailed immunization history is also required for every traveler to be able to complete vaccinations as per national public health recommendations.
- Many Asian adults may have acquired immunity against endemic diseases, such as hepatitis A, even though it is not included in their EPI, as natural infection was still common until recently. There is no data on vaccine preventable diseases, but evidence showed that while up to 30% of “Western” travelers developed travelers' diarrhea (TD) during their trip in Thailand, only 7% of travelers from East Asia and only 5% of travelers from other Southeast Asian countries developed TD there. This further reduces the perception of raised risk. Travel medicine practitioners should be aware of the local seroepidemiological conditions on pre-travel counseling; particularly the higher socio-economic strata who can afford to travel may not have acquired immunity by infection.
- Behavioral differences may also influence health risks. As mentioned, the risk of TD among Asian travelers who travel to other tropical destinations may be far lower than the rates observed in “Western” travelers and that may not be associated only with seroprevalence of antibodies. In the destination country, Asian travelers often will stay in other places than those visited by “Western” ones. This may be associated with differing purpose of travel; many Asians for instance visit sites for religious reasons or visit friends and family, while “Westerners” may more often select adventure and rural travel.
|DTP||MMR||Polio vaccine||JE vaccine||Hepatitis B vaccine||Hepatitis A vaccine||Seroprevalence of hepatitis A† (%)||EPI |
|USA||√||MMR||IPV||0||√||√||30 general pop.||95|
|Canada||√||MMR||IPV||0||√||High risk||40–60 (40+ y)||80|
|UK||√||MMR||IPV||0||High risk||0||>60 (50–59 y)||96|
|France||√||MMR||IPV||0||√||0||29 (20–29 y)||99|
|Germany||√||MMR||IPV||0||√||0||64 (50–59 y)||93|
|Italy||√||MMR||IPV||0||√||High risk||<10 young adult||96|
|Australia||√||MMR||IPV||0||√||High risk||50 (by age 40)||92|
|New Zealand||√||MMR||IPV||0||√||0||<20 (36–55 y)||93|
|China||√||MMR||OPV||√||√||√||>50 (10–19 y)||99|
|South Korea||√||MMR||IPV||√||√||0||<10 in children||94|
|Japan||√||MMR||OPV||√||0||0||4 (20–29 y)||98|
|India||√||MMR||OPV||Partly||√||0||>95 (by age 10 y)||72|
|Thailand||√||MMR||OPV||√||√||0||>90 (by age 30 y)||99|
|Vietnam||√||Measles||OPV||Partly||√||0||>95 (5–9 y)||93|
|Singapore||√||MMR||OPV||0||√||0||>50 (40–49 y)||97|
|Indonesia||√||Measles||OPV/IPV||0||√||0||95 (by age 10)||83|
|Malaysia||√||MMR||OPV||√||√||0||88 (41–60 y)||94|
|Philippines||√||MMR||OPV||0||√||0||>99 (age 40+ y)||87|
In conclusion, while there is a well-established evidence base regarding the incidence rates of health problems among travelers originating from Europe, the United States, Canada, and Australia to developing countries, it is not justified to apply these rates to Asian travelers. It would also be inappropriate to apply the same risk recommendations to most travelers originating from Latin America and Africa. Their hosts and their environmental factors differ.
More research focusing on Asian travelers is urgently needed, as fundamental data on destinations, purpose of travel, duration of stay, intensity of contact with the local population, risk of illness and accidents, etc. are almost nonexistent. Not only risks pertaining to international travel but those of an individual leaving an upper-class residential area in Mumbai to go to the interior jungles of India may also be considerable. Asian travelers deserve a better protection similar to “Western” travelers, but it must be evidence based. On the basis of such evidence, it will help raise awareness and actively propagate travelers' health in Asia, and convince both travelers and professionals about the need of travel health advice and preventive measures.
Travel medicine practitioners should start to consider that travel no longer occurs only from North to South or West to East. People, as well as pathogens, travel from all around the world in all directions. Travelers from Asia, Africa, and Latin America have become an important population; they now need specific and careful assessment on where there are excessive health risks associated with travel, to conclude for which trips they need specific travel health advice.