Dengue vaccine has been registered and is now available in some hospitals in Thailand. Some travelers ask whether they should get dengue vaccine or not and what is recommended.
The simple answer to this question is for those who live/ work in Thailand (the expat), you should have lived in Thailand (or in the tropics) at least 9 years in order to get the vaccine, but generally not for travellers. Scientists believe when people get primary (1st time) infection with dengue virus, the disease is usually mild and self-limited. However, if that patient gets dengue infection again (secondary infection), there is an increase risk to develop more severe disease.
However, it doesn’t mean that all patients with secondary dengue infection will be severe. In fact, the majority of the cases is still mild
, but chances to develop severe disease is higher than primary infection. Ideally dengue vaccine should create a lifelong immunity against all four serotypes of dengue virus.
If we have that kind of vaccine, that’s fantastic. Unfortunately, we do not live in an ideal world. However, when talking about the efficacy, it is not excellent. The overall efficacy of vaccine against all serotypes of dengue virus was around 65%. That means even you get the vaccine you still have a chance to get dengue infection, it could actually reduce to risk approximately 65%. Before the vaccine became commercially available, it was been used in more than 30,000 healthy volunteers who were mainly children.
Researchers found that younger children (age less than 9 years) responded poorly to the vaccine when compared to older children or adult. Moreover, during the study, researchers found a warning signal that might suggest that giving the vaccine to young children may not be good. So this is why the FDA set the lower age limited for dengue vaccine to 9 years old.
Dengue vaccine trials in Thailand Research also showed that children who have been exposed to dengue virus actually responded better than those who never exposed to dengue virus before. It is likely that children at age less than 9 years may never been bitten by an infected mosquito (i.e. never exposed to virus). This group of children will get less benefit of the vaccine. So it is not recommended to use in this group.
This research result can apply to traveler groups. For someone visiting Thailand for the first time who has never been exposed to dengue virus it is not recommended to give the vaccine as the benefit is less and there may be a safety concern as well. The World Health Organization (WHO) recommends dengue vaccine in people age 9-45 years old who live in the dengue endemic area. There is no recommendation for travelers. For those who live in Thailand (Expat), the vaccine is given only to those who have stayed here at least 9 years. This group of expats might already have been exposed to dengue virus (equivalent to local children age 9). If they just live here in Thailand for 1 year, we will not give (equivalent to children age 1).