Dengue is Vietnam's everyday mosquito risk. Here's how it changes from north to south.
Dengue is reported in every month, and 2026 is running about 37% above last year, with most cases in the south. CDC lists malaria medicine for rural areas only, not the big cities, and Japanese encephalitis is a question for long or rural trips.
Dengue is the everyday risk in Vietnam. It is reported in every month, 2026 is running about 37% above 2025, and most cases are in the south, around Ho Chi Minh City and the Mekong Delta. The mosquito that spreads it bites in daylight, so repellent goes on in the morning over sunscreen and again before sunset. CDC reports no malaria in Hanoi, Da Nang or Ho Chi Minh City and recommends no medicine for the Mekong and Red River Deltas. Rural treks, homestays outside the deltas and long stays are a question for a travel clinic 4–6 weeks before you fly, for malaria and Japanese encephalitis alike.
The classic first trip to Vietnam runs from Hanoi and an overnight cruise on Ha Long Bay in the north, through Hoi An and Da Nang on the central coast, to Ho Chi Minh City (Saigon) and the Mekong Delta in the south, sometimes with a beach stay on Phu Quoc. Americans make it in every month, and the bug picture shifts along the way. The north and center are moderate, the south carries most of this year's dengue, and the worst bites come on Phu Quoc's quieter beaches.
Dengue is the everyday item
Dengue is endemic across Vietnam, and the country is on CDC's global dengue list, a Level 1 notice for countries reporting more cases than usual or more cases than expected among returning US travelers. This is its second rising year. 2025 ended with 184,903 cases, 28.4% more than 2024, after a weekly peak of about 8,000 cases in August. Through September 20, 2026, the World Health Organization's Western Pacific office, reporting Ministry of Health figures, counted 131,202 cases and 18 deaths, against 95,469 cases at the same point in 2025. Weekly counts were still edging up in mid-September.
WHO puts about 71% of 2026 cases in the southern region, around Ho Chi Minh City and the Mekong Delta. Hanoi and the central coast have dengue too, but this year's surge is concentrated in the south.
The Aedes mosquitoes behind it breed in small pools of standing water and bite in daylight, with peaks after sunrise and before sunset. Our dengue & Zika daily routine has the full schedule. On a Vietnam trip it comes down to three habits.
Before the street-food walk, the pagoda or the boat. Sunscreen first; repellent on top.
Heat, sweat and a swim shorten any label's protection window. Count a soaked shirt as a reset.
It runs into riverside dinners in Hoi An and the Mekong. Do ankles and calves too.
North, center and south
Vietnam's regions keep different weather calendars. December to April is the easiest window for the whole route; the other dates below are approximate, and dengue is reported in every month everywhere.
North: Hanoi and Ha Long Bay. The cool months, roughly December to April, are usually the easiest time for bites. On a cruise, the island and cave stops tend to bite more than the boats.
Center: Hoi An and Da Nang. The wet season runs roughly from late summer into December. Bites gather along Hoi An's river and on countryside bike rides, and riverside dinners fall in the late-afternoon peak.
South: Ho Chi Minh City, the Mekong Delta and Phu Quoc. The rains run roughly May to November, and dengue tends to peak from July to October. With about 71% of 2026's cases in this region, the morning repellent matters most at this end of the trip.
Malaria is a rural question
CDC's traveler page for Vietnam describes malaria transmission in "rural areas only," with "rare cases in the Mekong and Red River Deltas." It reports none in the cities of Da Nang, Hai Phong, Hanoi, Ho Chi Minh City (Saigon), Nha Trang and Quy Nhon. For the two deltas it recommends no prevention medicine, only insect bite precautions and mosquito avoidance.
CDC lists prevention medicines for all other areas with malaria transmission, with a narrower list for ten provinces: Bình Dương, Bình Phước, Đắk Lắk, Đắk Nông, Gia Lai, Khánh Hòa, Kon Tum, Lâm Đồng, Ninh Thuận and Tây Ninh. Those names date from before Vietnam's 2025 province mergers, so some no longer match a current map. The page also doesn't say how "rural areas only" applies to places such as Ha Long Bay's islands, Hoi An's outskirts, Da Lat or Phu Quoc.
Hanoi · Ha Long Bay · Hoi An & Da Nang · Saigon · Mekong Delta
Hanoi, Da Nang and Saigon are on CDC's no-malaria list, and CDC recommends no medicine for the deltas.
- Ask a clinic about Ha Long Bay's islands and Hoi An's outskirts, which CDC doesn't name
- A bed net or screened room at Mekong homestays
- No Japanese encephalitis vaccine advised for short city stays
Northern highland treks · rural homestays · the ten listed provinces
This is where CDC lists malaria medicine and suggests considering Japanese encephalitis vaccine.
- Travel clinic 4–6 weeks out with your exact route
- Permethrin-treated clothes for treks and village nights
- Repellent at dusk as well as by day
What we suggest you do with this: if your trip goes beyond the cities and the deltas, to treks, rural homestays or anywhere in the provinces above, book a travel-medicine appointment 4–6 weeks before departure. Bring your exact route, with the number of nights in each place, and ask the clinic to match CDC's province names to it. None of this applies to a city-only trip. Our malaria-zone checklist covers the rest.
Whatever the clinic decides, malaria mosquitoes bite from dusk to dawn. Repellent at sunset, long sleeves for evenings in the countryside and an air-conditioned or screened room, or a net, cover most of that exposure.
Japanese encephalitis: a long-stay and rural question
Japanese encephalitis is a mosquito-borne virus present in Vietnam. CDC recommends the vaccine for travelers moving to an area with the virus, spending a month or more in such areas, or traveling there often. It suggests considering it for shorter stays that include rural areas, hiking or camping, or nights without air-conditioning, screens or bed nets, and for travelers unsure of their plans or how long they'll stay. It does not recommend it for short trips to cities. One clinic visit can settle this and malaria together.
Where you're going
Here is how the main stops compare across the year.
Hanoi
CDC lists no malaria in the city and does not recommend Japanese encephalitis vaccine for a short urban stay. Dengue is present, though this year's surge is concentrated in the south.
Ha Long Bay
Travelers tend to report few mosquitoes on the overnight boats out on the salt water and more at the island and cave stops. Put repellent on before you go ashore.
Hoi An & Da Nang
CDC names Da Nang among the cities with no malaria; Hoi An town isn't named. Bites gather along the river and on countryside bike rides, so reapply before an afternoon ride.
Ho Chi Minh City (Saigon)
No malaria in the city, per CDC. The southern region has about 71% of Vietnam's 2026 dengue cases, so the daytime routine matters most here.
Mekong Delta
Inside the southern dengue surge. CDC reports rare malaria and recommends no medicine here, only bite precautions; homestays usually provide nets, and rural stays are where CDC suggests considering Japanese encephalitis vaccine.
Phu Quoc
Sand flies on Sao Beach and some quieter beaches are the main complaint, worst in the early evening. The island belongs to the Mekong Delta region, where CDC recommends no malaria medicine, though CDC doesn't name Phu Quoc itself.
Rivers, homestays and Phu Quoc's sand flies
Forum posters tend to describe Hoi An and the cities as manageable. Bites gather along rivers, in the countryside at dusk and on Mekong homestay nights.
Phu Quoc is the exception. Sand flies on Sao Beach and some of the island's quieter beaches are the main complaint in reviews, and posters say they're worst in the early evening. Put repellent on your ankles and lower legs before an afternoon on the sand, and use a lounger instead of lying on the sand. Our sand fly guide explains how beach biters like these behave.
What travelers report
Paraphrased from forum threads and reviews and linked so you can read them in full. None is dated, and trips vary with the season, the weather and where you stay.
- Hoi An
A poster who had just come from Siem Reap found Hoi An's mosquitoes mild by comparison. Another reply said the worst of them were along the river, near the riverside resorts. TripAdvisor ↗
- Hoi An
A traveler bitten in Hoi An worried about dengue. Replies said only one mosquito species carries it and the chance of infection from any one bite is low, but still advised repellent. TripAdvisor ↗
- Sao Beach, Phu Quoc
A Sao Beach reviewer warned other visitors about sand flies in the sand there. TripAdvisor ↗
- Mango Bay Resort, Ong Lang, Phu Quoc
A guest was still recovering from bites picked up on the beach and on the bungalow veranda, and suspected sand flies. TripAdvisor ↗
The Vietnam kit
- Picaridin 20% travel sprays: odorless in the heat, layers over sunscreen and is easy to aim at ankles and calves on Phu Quoc's beaches. One 3.4 oz bottle covers about a week of daily use for one person.
- A full-size backup in the checked bag for a two- or three-week trip, so you're not hunting for a familiar brand halfway down the coast.
- Permethrin 0.5% for clothes: treat a long-sleeved shirt, trousers and socks at home 48 hours before you fly. Treated fabric repels and kills mosquitoes on contact through several washes, which suits dusk-to-dawn hours in the countryside.
If the trip continues to Siem Reap or Bangkok, our Cambodia briefing covers a 2026 dengue epidemic there, and our Thailand briefing maps CDC's malaria advice.
Two last notes. If you're pregnant, talk to your healthcare provider before the trip, because Zika has circulated in Vietnam. And any fever during or after your trip means a doctor visit, and you tell them you were in Vietnam. Dengue usually shows up within two weeks; malaria can take longer.
Traveler questions
Do I need malaria pills for Vietnam?
CDC reports no malaria in the cities of Da Nang, Hai Phong, Hanoi, Ho Chi Minh City, Nha Trang and Quy Nhon, and recommends no prevention medicine for the Mekong and Red River Deltas, only bite precautions. It lists medicine for rural areas elsewhere, with a narrower drug list for ten named provinces whose names predate Vietnam's 2025 province mergers. If your route goes beyond the cities and deltas, or includes places CDC doesn't address directly, such as Ha Long Bay's islands, Hoi An's outskirts, Da Lat or Phu Quoc, take it to a travel clinic 4–6 weeks before departure. None of this applies to a city-only trip.
How bad is dengue in Ho Chi Minh City?
The southern region, which includes Ho Chi Minh City and the Mekong Delta, has about 71% of Vietnam's 2026 dengue cases, in a year running about 37% above 2025, according to the World Health Organization. WHO's update doesn't give a figure for the city itself. In practice, the daytime routine matters most at the southern end of the trip: repellent over sunscreen after breakfast, again after a swim or a sweaty afternoon, and again before sunset.
Should I get the Japanese encephalitis vaccine for Vietnam?
CDC does not recommend it for short trips to cities. It recommends it for travelers moving to an area with the virus, spending a month or more in such areas or traveling there often, and suggests considering it for shorter stays that include rural areas, hiking, camping or nights without air-conditioning, screens or bed nets. A Mekong homestay or a rural trek can put a short trip in that group. Decide with a travel clinic 4–6 weeks before departure.
Are there mosquitoes on a Ha Long Bay cruise?
Travelers tend to report few on the overnight boats themselves, out on the bay's salt water, and more at the island and cave stops. Put repellent on before you go ashore and again for an evening stop. CDC's malaria page doesn't say how its "rural areas only" wording applies to the bay's islands, so mention the cruise if you're seeing a travel clinic anyway.
What bites on Phu Quoc's beaches?
Mostly sand flies. They are the main complaint in reviews of Sao Beach and some of the island's quieter beaches, and posters say they're worst in the early evening. Put repellent on your ankles and lower legs, use a lounger instead of a towel on the sand, and shower after the beach. Dengue mosquitoes are there too, as everywhere in the south, so keep the daytime routine.
I'm pregnant. Is there Zika in Vietnam?
CDC has no Zika notice for Vietnam. Zika did circulate in the south in 2016, when the first locally acquired cases were found in Nha Trang and Ho Chi Minh City, and CDC lists it among the diseases relevant to travelers to Vietnam, including spread from a pregnant woman to her baby. Talk to your healthcare provider before the trip.
Sources
Health authorities, surveillance reports and news coverage of official bulletins used for this briefing, last checked October 2026. Traveler reports are linked where they appear. This page summarizes public-health guidance and is not medical advice.