Dengue is endemic in Vietnam, with more cases in and after the rainy season. For most people it is a rough week: high fever, a bad headache, pain behind the eyes, aching muscles and joints, sometimes a rash. Most recover without complications. But a minority get worse at a point that catches people out — and the way to avoid that is knowing which signs matter and when to stop waiting.
Before anything else
Go to a hospital or call 115 IMMEDIATELY if you have: severe or worsening abdominal pain, vomiting that will not stop, bleeding from the gums or nose, blood in vomit or black stools, bruising without injury, very little urine, cold or clammy hands and feet, restlessness or unusual drowsiness, or difficulty breathing. In dengue these are not "wait and see" symptoms.
What the first days usually look like
Symptoms typically begin four to ten days after the mosquito bite, so the bite that caused it is usually long forgotten. The illness tends to run in phases, and knowing them is what makes the difference:
| Phase | Roughly when | What it feels like | What matters |
|---|---|---|---|
| Febrile | Day 1–3 | Sudden high fever, severe headache, pain behind the eyes, muscle and joint aches, nausea, sometimes a flushed rash | Fluids and rest; confirm the diagnosis; avoid NSAIDs |
| Critical | Around day 3–7, as the fever falls | Fever drops and you may feel briefly better — but this is when fluid can leak from blood vessels and platelets fall fastest | This is the window to be monitored, not the window to resume your itinerary |
| Recovery | Day 7 onward | Appetite returns; sometimes an itchy rash as the skin recovers; tiredness can last weeks | Resume activity gradually |
The counter-intuitive part is worth repeating: in dengue, the fever breaking is not the all-clear. The critical phase begins roughly when the temperature comes down. If you feel suddenly worse after the fever falls, that is a reason to be seen urgently.
Dengue or just a bad flu?
You cannot tell reliably from symptoms alone, and in Vietnam it matters enough to check rather than guess. A few patterns point towards dengue rather than a respiratory illness:
- Fever comes on suddenly and high, rather than building over days
- Pain behind the eyes, and muscle and joint aches out of proportion to the rest
- Little or no cough, runny nose or sore throat — dengue is not usually a respiratory illness
- A flushed appearance early, or a rash appearing as the fever settles
- You have been in an area with mosquitoes in the previous one to two weeks
A blood test settles it. In the first days an NS1 antigen test is commonly used; from around day five, antibody tests become informative. A full blood count also shows the two things clinicians watch in dengue: the platelet count and the haematocrit. One test on one day is a snapshot — what matters is the trend, which is why repeat testing is often more useful than a single result.
⚠️ The one medication mistake to avoid
Do not take ibuprofen, aspirin, naproxen, diclofenac or other NSAIDs if dengue is possible. They affect platelets and the stomach lining, and dengue already lowers platelets — the combination raises the bleeding risk. Paracetamol (acetaminophen) is the usual choice for fever and pain, within the dose on the packet. If you have already taken an NSAID, say so when you are assessed; do not hide it.
There is no antiviral that treats dengue. Everything that helps is supportive: enough fluid, rest, controlling fever safely, and watching for the warning signs. That is also why "a drip to cure dengue" is not a thing — fluids help when you cannot drink enough or there are signs of leakage, and that is a clinical decision, not a menu item.
What can be done where you are staying
Mild dengue is usually managed at home or in your accommodation, provided someone is watching the warning signs and you can keep drinking. What a visiting clinician can do on site:
- Examine you and decide whether this needs hospital assessment now or monitoring is reasonable
- Take blood for a full blood count and dengue testing, and repeat it over the following days to see the trend
- Give fluids by IV when oral intake is not keeping up — by indication, with monitoring while it runs
- Advise on safe fever control, and what specifically to watch for overnight
- Issue an itemised invoice and a medical report in English for a travel-insurance claim
Not sure whether what you have needs a hospital? That is worth checking rather than guessing. Call +84 94 368 81 15 (24/7) or leave your details and we will confirm what can be done where you are. This is not an emergency service — for the warning signs above, go to a hospital or call 115.
When hospital is the right answer, not a home visit
- Any of the warning signs in the box at the top of this page
- A platelet count that is falling fast, or a rising haematocrit alongside it
- You cannot keep fluids down at all, or you are passing very little urine
- Young children, pregnant women, older adults, or anyone with diabetes, heart, kidney or liver disease, or on blood thinners — these groups should be assessed earlier and more readily
- A second episode of dengue: a repeat infection with a different strain carries a higher risk of the severe form
Avoiding the bite in the first place
The mosquito that carries dengue bites during the day, with peaks in the early morning and the hours before dusk. That is the opposite of the malaria mosquito, and it is why "I slept under a net" is not full protection here.
- Use repellent on exposed skin during the day, not only in the evening
- Prefer accommodation with screens or air conditioning, and keep doors closed at dusk
- Empty standing water around where you are staying — buckets, plant trays, bottle caps; the larvae need very little
- Cover up in the early morning and late afternoon, especially near greenery and water
- If someone you are travelling with has dengue, protect them from further bites too — that is how it spreads onward
Paperwork, if you are travelling
If you have travel insurance, call the assistance line on your policy early — the operator logs the case, tells you which facility to use and confirms whether direct payment applies. If you pay yourself and claim later, ask during the visit for an itemised invoice and a medical report in English stating the diagnosis, tests done and treatment given, and photograph both in case the paper copies go missing. Getting this after you have left Vietnam is much harder.
