Dengue fever is an acute viral illness transmitted to humans by female mosquitoes of the genus Aedes — specifically Aedes aegypti and Aedes albopictus. Colloquially these mosquitoes are called "tiger mosquitoes": they're a bit smaller than ordinary ones and have a striped pattern. They're not exclusive to Thailand, of course. The planet's tropical and subtropical belts are, one way or another, all at risk from the fever — you can find these females in Africa, South America, and Central Asia too. Male mosquitoes, incidentally, don't feed on blood at all. They prefer nectar.
If you own a home in Thailand, a few preventive measures are worth following: first, keep water containers covered to stop new mosquitoes from being born; change the water in flower vases every 7 days so larvae can't develop. Don't let water sit and stagnate — old pots, tires. Use small fish anywhere water is kept as decoration; they eat mosquito larvae. If you don't have fish, add special sterilizing agents to standing water — they're inexpensive. Second, protect your sleep with a mosquito net, especially during the day, and wear covering clothing. And finally, use repellents and fumigators. Fever season is approaching — it runs from June to September, a period rich in rain, which means plenty of standing water. Even though most infections happen in that June–September stretch, isolated cases are recorded year-round, so prevention matters at all times.
What makes dengue dangerous?
The female mosquito that carries the virus is most active in the morning and daytime hours. You might not even notice the bite, but a week later you'll likely realize it happened. When I had dengue myself back in February 2013, I also happened to have a broken leg and was on crutches. "Walking" is a generous word — I spent a week lying down with a fever of 38–39°C, aching all over, unable to eat or drink, since dengue also brings on every symptom of stomach poisoning. Sometimes migraines too. Eat or drink anything and you're violently sick. That's how the body dehydrates to the max. There was no vaccine back then, and the doctor could only shrug and advise drinking more water to maintain proper hydration — in practice, so there'd be something to keep bringing up. And don't skip the paracetamol — it can at least bring the fever down. I didn't get a rash, and it's worth noting this was my primary infection, which for most people is relatively mild. Yet statistics show a 1–5% fatality rate from hemorrhagic dengue fever and dengue shock syndrome. Without medical help, they really can be fatal.
Once I felt better I went to the hospital and learned that the virus has four strains, and I'd had one of them. I now have lifelong immunity to that one — but I'm still vulnerable to the other three, and now with an even higher risk of a fatal outcome! That's because of a phenomenon called antibody-dependent enhancement (ADE): antibodies formed earlier bind to the new strain but fail to neutralize it — instead, they help it enter immune cells.
It's precisely because of how these antibodies behave that the French vaccine Dengvaxia, released in 2015, requires a prior infection as a precondition for vaccination. Otherwise the vaccine won't work, and your first-ever infection will hit you with the full bouquet of secondary-infection symptoms. The vaccine is intended for children and adults aged 9 to 45 and is given in stages: three doses spaced six months apart. So if you decide to get vaccinated in April, you'll need another dose in October, and another the following April — over the course of a year, you'll build up full immunity to the fever. Dengvaxia's efficacy, however, is only around 60%.
Later, in 2022, some countries approved the Japanese vaccine Qdenga. It's a live attenuated vaccine that works against all four serotypes, meaning prior infection isn't required. It's approved for adults and children from age 4. And unlike the French vaccine, it only takes two doses, three months apart. Its efficacy is around 80%, and consulting a doctor or running extra tests beforehand isn't required.
In 2023–2024, Thailand went through a major dengue outbreak: the provinces of Chiang Mai, Udon Thani, and Phuket itself all recorded a threefold jump in infections compared to previous years. Partly because of that, Qdenga was registered in Thailand in 2024 as well, alongside the EU, the UK, and several South American countries.
The vaccine is now available to everyone aged four and up. So right now, you and your entire family have the chance to rule out dengue infection completely — just remember that the vaccination course runs over three months.
If you own a home in Thailand, a few preventive measures are worth following: first, keep water containers covered to stop new mosquitoes from being born; change the water in flower vases every 7 days so larvae can't develop. Don't let water sit and stagnate — old pots, tires. Use small fish anywhere water is kept as decoration; they eat mosquito larvae. If you don't have fish, add special sterilizing agents to standing water — they're inexpensive. Second, protect your sleep with a mosquito net, especially during the day, and wear covering clothing. And finally, use repellents and fumigators. Fever season is approaching — it runs from June to September, a period rich in rain, which means plenty of standing water. Even though most infections happen in that June–September stretch, isolated cases are recorded year-round, so prevention matters at all times.
What makes dengue dangerous?
The female mosquito that carries the virus is most active in the morning and daytime hours. You might not even notice the bite, but a week later you'll likely realize it happened. When I had dengue myself back in February 2013, I also happened to have a broken leg and was on crutches. "Walking" is a generous word — I spent a week lying down with a fever of 38–39°C, aching all over, unable to eat or drink, since dengue also brings on every symptom of stomach poisoning. Sometimes migraines too. Eat or drink anything and you're violently sick. That's how the body dehydrates to the max. There was no vaccine back then, and the doctor could only shrug and advise drinking more water to maintain proper hydration — in practice, so there'd be something to keep bringing up. And don't skip the paracetamol — it can at least bring the fever down. I didn't get a rash, and it's worth noting this was my primary infection, which for most people is relatively mild. Yet statistics show a 1–5% fatality rate from hemorrhagic dengue fever and dengue shock syndrome. Without medical help, they really can be fatal.
Once I felt better I went to the hospital and learned that the virus has four strains, and I'd had one of them. I now have lifelong immunity to that one — but I'm still vulnerable to the other three, and now with an even higher risk of a fatal outcome! That's because of a phenomenon called antibody-dependent enhancement (ADE): antibodies formed earlier bind to the new strain but fail to neutralize it — instead, they help it enter immune cells.
It's precisely because of how these antibodies behave that the French vaccine Dengvaxia, released in 2015, requires a prior infection as a precondition for vaccination. Otherwise the vaccine won't work, and your first-ever infection will hit you with the full bouquet of secondary-infection symptoms. The vaccine is intended for children and adults aged 9 to 45 and is given in stages: three doses spaced six months apart. So if you decide to get vaccinated in April, you'll need another dose in October, and another the following April — over the course of a year, you'll build up full immunity to the fever. Dengvaxia's efficacy, however, is only around 60%.
Later, in 2022, some countries approved the Japanese vaccine Qdenga. It's a live attenuated vaccine that works against all four serotypes, meaning prior infection isn't required. It's approved for adults and children from age 4. And unlike the French vaccine, it only takes two doses, three months apart. Its efficacy is around 80%, and consulting a doctor or running extra tests beforehand isn't required.
In 2023–2024, Thailand went through a major dengue outbreak: the provinces of Chiang Mai, Udon Thani, and Phuket itself all recorded a threefold jump in infections compared to previous years. Partly because of that, Qdenga was registered in Thailand in 2024 as well, alongside the EU, the UK, and several South American countries.
The vaccine is now available to everyone aged four and up. So right now, you and your entire family have the chance to rule out dengue infection completely — just remember that the vaccination course runs over three months.
How to protect yourself from tropical fever?
Dengue Season? There's a Vaccine
Original text translated by Claude
