Dengue is the mosquito-borne infection foreign residents in Vietnam are most likely to meet. It occurs all year in the south and peaks during the rainy months, roughly from mid-year into late autumn across much of the country, with the north seeing most cases in summer and autumn. It is spread by Aedes mosquitoes, which bite mainly during the day and breed in small pools of clean standing water around homes. Most cases are unpleasant but recover with rest and fluids; a small proportion become severe, and the danger often appears as the fever is falling. Anyone with a high fever in Vietnam should see a doctor rather than self-treat.
This guide explains how dengue behaves, why the usual pain-relief habits can be risky, which warning signs need urgent care, and how to make an apartment or house far less attractive to the mosquitoes that carry it. It is general information drawn from public health guidance by the World Health Organization and Vietnam's Ministry of Health, not medical advice.
What dengue is and how it spreads
Dengue is a viral infection caused by four closely related dengue viruses. It is transmitted from person to person by the bite of infected female Aedes mosquitoes, mainly Aedes aegypti, which lives close to people in towns and cities. The World Health Organization describes dengue as one of the fastest-spreading mosquito-borne diseases in the world, and Vietnam is among the countries in Southeast Asia where it is endemic, meaning it circulates every year.
Two features of the mosquito shape everything about prevention. First, it bites during daylight, especially in the early morning and late afternoon, so a bed net at night protects less than people expect. Second, it breeds in small containers of relatively clean water: plant saucers, buckets, water jars, blocked gutters, discarded cups, old tyres and the trays under refrigerators and air conditioners. A single neglected flower vase can produce mosquitoes for a whole floor.
Because there are four types of the virus, a person can be infected more than once. A second infection with a different type carries a higher risk of severe disease. That is one reason people who have lived in the region for a long time should not assume they are protected because they had dengue before.
The pattern across the year
Dengue activity varies from year to year, and local health authorities announce outbreaks when cases rise. The broad pattern below is a guide to when to be most careful, not a forecast.
| Region | Usual dengue pattern | What it means for residents |
|---|---|---|
| The south, including Ho Chi Minh City and the Mekong Delta | Cases all year, rising with the rainy season from around May and highest in the second half of the year | Prevention is a year-round habit, intensified in the wet months |
| The central coast, including Da Nang and Hoi An | Rainy season comes later, in autumn and early winter; cases often rise in the later part of the year | Watch the weeks after heavy rains and flooding |
| The north, including Hanoi | Few cases in the cool months, with most in summer and autumn | Expect a seasonal rise from mid-year |
| Central Highlands, including Da Lat | Cooler climate at altitude means fewer mosquitoes, but cases occur, especially in lower areas | Less risk, not no risk |
Outbreak years can bring dengue earlier and in larger numbers than usual. Local news and notices from the provincial health department are the best signal that it is time to step up prevention.
Recognising dengue and the warning signs
The typical illness. Dengue often starts suddenly with a high fever, severe headache, pain behind the eyes, muscle and joint aches, nausea and sometimes a rash. Some people have only mild symptoms. Because many infections look similar in the first days, a doctor will usually order blood tests to confirm dengue and check blood counts.
The critical phase. In a small proportion of patients, severe dengue develops, often around the time the fever starts to drop, typically three to seven days into the illness. Feeling slightly better at this point is not proof of recovery.
Warning signs to act on immediately. Severe abdominal pain, persistent vomiting, bleeding from the gums or nose, blood in vomit or stools, rapid breathing, unusual tiredness or restlessness, and cold or clammy skin. Any of these means going to hospital straight away.
Who needs extra care. Infants, pregnant women, older adults, people with chronic conditions such as diabetes or heart disease, and anyone who has had dengue before should be seen promptly and followed closely by a doctor.
Why pain relief needs care
There is no specific antiviral treatment for dengue. Care focuses on rest, fluids and close monitoring, and in severe cases careful fluid management in hospital, which is why early medical assessment matters so much. A doctor will advise on what to take for fever and pain.
Public health guidance, including from the World Health Organization, warns against using certain common painkillers, such as aspirin and ibuprofen and other non-steroidal anti-inflammatory drugs, when dengue is possible, because they can increase the risk of bleeding. Many people keep these at home without thinking about it. If you develop a fever in Vietnam, ask a doctor before taking anything, rather than reaching for what you would use for flu at home.
Drinking enough is important. Oral rehydration solutions, water, soups and fruit juices all help. If the patient cannot keep fluids down, urinates very little, or seems drowsy, that is a reason to go to hospital.
Making your home less friendly to Aedes mosquitoes
Most Aedes mosquitoes that bite you were born within a short distance of where you live. A weekly routine removes most of their breeding sites.
- Once a week, walk around your home, balcony and garden and empty, scrub or turn over anything holding water: plant saucers, buckets, pet bowls, vases and toys.
- Change water in vases every few days and rinse the inside, since eggs stick to the walls of containers.
- Cover water storage jars and tanks tightly, or add a fine mesh.
- Check gutters, drains, refrigerator drip trays and air-conditioner condensate trays, which are easy to forget.
- Fit or repair window and door screens, and keep doors closed in the late afternoon.
- Ask your building manager about common areas, such as rooftop tanks, basement car parks and construction debris nearby.
Local health authorities run clean-up campaigns and sometimes fogging during outbreaks. Fogging kills adult mosquitoes for a short time but does not reach eggs and larvae, so removing standing water remains the most effective step.
Personal protection during the day
Because Aedes mosquitoes bite in daylight, protection has to cover the times you are out and about: school runs, morning markets, afternoon walks. Repellents containing ingredients such as DEET, picaridin (also called icaridin) or IR3535 are widely recommended by public health agencies. Follow the label for application and reapplication, particularly for children, and apply sunscreen first and repellent second.
Light-coloured clothing that covers arms and legs helps, as do fans, since mosquitoes are weak fliers. Air-conditioned rooms with closed windows have fewer mosquitoes. For babies and young children, nets over cots and strollers during daytime naps add protection.
Outdoor workers, runners, cyclists and parents at playgrounds tend to be bitten most, because they are outside at exactly the hours Aedes is active. Treating clothing with permethrin, which some outdoor shops sell, is another layer used by people who spend long periods outdoors; follow the product instructions closely and do not apply it to skin.
A dengue vaccine has been licensed in Vietnam in recent years. Whether it suits you depends on your age, health and history of infection, and recommendations vary by country. Ask a doctor or vaccination clinic whether it is appropriate for you or your children, rather than relying on general advice.
Other mosquito-borne infections to know about
Dengue is not the only infection mosquitoes carry in Vietnam. Japanese encephalitis, spread by Culex mosquitoes mostly in rural areas where rice paddies and pig farming are common, is rare but serious, and a vaccine is available; whether you need it depends on where and how you live. Chikungunya and Zika, also spread by Aedes mosquitoes, have been reported in the region. Zika is a particular concern in pregnancy, and couples planning a pregnancy should ask a doctor about it.
Malaria risk in Vietnam is low and concentrated in some remote forested and border areas, not in the cities where most foreigners live. Residents who travel to remote areas should ask a travel medicine doctor whether any precautions are needed for the specific trip.
Ticks and other biting insects in forests and grassland can also carry infections, including scrub typhus, which is reported in rural Vietnam. If you hike or camp, wear long trousers tucked into socks, use repellent, check your body afterwards, and tell a doctor about your outdoor trip if you fall ill with a fever in the following weeks.
The good news is that the household routine and personal protection described above reduce the risk of all of these infections at once.
If a doctor diagnoses dengue
Most adults with dengue are managed at home, with clear instructions and repeat blood tests to track platelet counts and signs of fluid leakage over the following days. The doctor may ask you to return daily, or sooner if warning signs appear. Patients in higher-risk groups, or those whose tests are worrying, are often admitted to hospital for observation, and the large public infectious disease hospitals in the big cities treat great numbers of dengue patients every year.
At home, the patient should rest, drink steadily throughout the day, and be watched by someone else, particularly around the time the fever falls. Keep a simple note of temperature, fluids taken and how often the patient urinates; this is exactly what the doctor will ask about at the next visit.
Recovery can leave people tired for several weeks. It is sensible to ease back into work and exercise gradually. Let your insurer know early if you are admitted, since dengue admissions are common claims and the insurer can usually arrange direct billing.
Câu hỏi thường gặp
When is dengue season in Vietnam?
Dengue occurs year-round in the south, rising in the rainy season and usually peaking in the second half of the year. The north sees most cases in summer and autumn, and the central coast often later in the year after the autumn rains. Outbreak years can shift and intensify these patterns.
Can you get dengue more than once?
Yes. There are four types of dengue virus, and infection with one gives lasting protection only against that type. A later infection with a different type carries a higher risk of severe dengue, so people who have had it before should seek medical care early if they develop a fever.
Is there a vaccine for dengue in Vietnam?
A dengue vaccine has been licensed in Vietnam in recent years. Eligibility and recommendations depend on age, health and past infection, and guidance differs between countries. Ask a doctor or an established vaccination clinic whether it suits you or your children.
What should I do if I get a high fever in Vietnam?
See a doctor, who can test for dengue and other infections. Rest, drink plenty of fluids, and avoid aspirin and ibuprofen unless a doctor says otherwise, since they can increase bleeding risk in dengue. Go to hospital immediately if warning signs such as severe abdominal pain, bleeding or persistent vomiting appear.
Do bed nets protect against dengue?
Only partly. The mosquitoes that spread dengue bite mainly during the day, so nets help most for babies and young children during daytime naps. Removing standing water around your home, using repellent and covering skin when outdoors give broader protection.
Is Da Lat free of dengue?
Da Lat's altitude and cooler climate mean fewer mosquitoes and fewer cases than in lowland cities, but dengue is reported in the wider province, especially in warmer, lower areas. Basic precautions are still sensible, particularly when travelling to the coast or lowlands.