Dengue vaccine (Qdenga): can I get it after having dengue, and from what age can children have it?

Why vaccinate if you have already had dengue

There are four dengue serotypes. Recovering from one gives lifelong immunity to that serotype only, and cross-protection against the others for just a few months. After that, the partial antibodies left behind can make an infection with a new serotype worse. That is why a second dengue infection carries a higher risk of shock and bleeding than the first.

Qdenga (TAK-003) covers all four serotypes. In the pivotal trial of more than 20,000 children aged 4–16, among those previously infected the vaccine reduced symptomatic dengue by about 76% and hospitalisation by about 86%. People who have had dengue are therefore the group doctors most often recommend it for.

Just recovered from dengue: how long to wait

In the weeks after recovery the body still carries high, temporary cross-reactive antibodies. A live vaccine given during that window may be partly neutralised before it can do its job. The Pediatric Infectious Disease Society of Thailand therefore advises waiting at least 6 months after infection before the first dose. The doctor will ask when you were ill and decide case by case.

If you catch dengue between the first and second dose, tell the doctor; the second dose may be postponed on the same principle, without restarting the course.

Never had dengue: can I still have it?

Yes, and no antibody test is needed first, which is the main difference from the earlier vaccine. In people never infected, the vaccine protects well against serotypes 1 and 2, with more limited data for serotypes 3 and 4. The WHO therefore recommends it in high-transmission settings where most of the population has already been exposed. Thailand is one of those settings, Bangkok especially, with cases every year.

If you cannot remember whether you have had dengue, which is true of most adults in Thailand, you do not need to find out before vaccination. The doctor assesses age, where you live and overall health.

From what age can children have it, and up to what age for adults

Children under 4 cannot yet be vaccinated, so protection in toddlers still rests on preventing mosquito bites and removing breeding sites. For adults over 60 the vaccine is not yet licensed in Thailand; the doctor will consider individual cases.

Side effects you may notice

• Pain, swelling or redness at the injection site (the most common)
• Headache, muscle aches, tiredness or a mild fever within 1–3 days, more often after the first dose than the second
• Serious allergic reactions are very rare; the clinic keeps you for observation after the injection
• Because it is a live vaccine, women of childbearing age should avoid pregnancy for at least 1 month after each dose

Good to know: The vaccine does not replace bite prevention and does not protect against other mosquito-borne illnesses such as chikungunya and Zika. If you have a high fever for more than 2 days after vaccination, or any dengue warning sign, see a doctor. Read dengue symptoms and danger signs.

When in the year to have it

Dengue in Thailand peaks in the rainy season, roughly June to September, but occurs year-round. Because the course is two doses 3 months apart and immunity is complete after the second, starting early in the year gets you fully covered before the rains. If you start late, the first dose already gives partial protection, so there is no reason to wait for next year. See details and book at dengue vaccine, 4 serotypes.