Hanoi is easy on bites. Its dengue season peaks in the fall.

Yes, though most visitors find central Hanoi light on bites. The mosquito that matters is the day-biting Aedes that spreads dengue, and Hanoi's dengue season peaks from September to November. CDC reports no malaria in the city, and a short city stay doesn't call for the Japanese encephalitis vaccine.

Hanoi's dengue season

Hanoi's own Center for Disease Control counted 4,860 dengue cases from January 1 to mid-October 2026, with no deaths, Vietnamese press reported. That is ahead of 2025 but 3,876 below the 2021–2025 average for the period. In the week of October 9 to 16 the center recorded 509 cases, up from under 200 a week in late July. It describes September to November as the city's yearly peak.

Nationally, cases through September 20 were about 37% above 2025, with roughly 71% in the south, the World Health Organization reported, and Vietnam is on CDC's global dengue list, a Level 1 notice.

The Aedes mosquito bites in daylight, with peaks after sunrise and before sunset, in the Old Quarter's alleys, plant-filled cafés, temple courtyards and around Hoan Kiem Lake. Put repellent on after breakfast over sunscreen and again in the late afternoon, and choose an air-conditioned or screened room. Lakes tend to be the exception. Sitting by the water at dusk brings ankle bites from midges and mosquitoes, travelers say, so for a West Lake sunset, sit back from the water and cover your ankles.

Malaria, Japanese encephalitis and day trips

CDC places Vietnam's malaria in "Rural areas only; rare cases in the Mekong and Red River Deltas" and reports "None in the cities of Da Nang, Hai Phong, Hanoi, Ho Chi Minh City (Saigon), Nha Trang, and Quy Nhon." For the deltas it says "No chemoprophylaxis recommended (insect bite precautions and mosquito avoidance only)." Ninh Binh, the Tam Coc and Trang An day-trip area, lies in the Red River Delta region, though CDC doesn't name it.

CDC's Vietnam page gives its Japanese encephalitis vaccine advice in three tiers.

• "Recommended for travelers who" "Are moving to an area with Japanese encephalitis to live," "Spend long periods of time, such as a month or more, in areas with Japanese encephalitis" or "Frequently travel to areas with Japanese encephalitis."
• "Consider vaccination for travelers" "Spending less than a month in areas with Japanese encephalitis but will be doing activities that increase risk of infection, such as visiting rural areas, hiking or camping, or staying in places without air conditioning, screens, or bed nets" or "Going to areas with Japanese encephalitis who are uncertain of their activities or how long they will be there."
• "Not recommended for travelers planning short-term travel to urban areas or travel to areas with no clear Japanese encephalitis season."

On a Ha Long Bay cruise, apply before the island and cave stops. CDC doesn't recommend the yellow fever vaccine, and Vietnam doesn't require it.

When to go

The cool, drier months, roughly December to April, are the easiest for bites. Dengue builds through the summer rains to its September–November peak, so August to November is the hardest stretch. Dengue is reported in every month.

Where you're going

Continuing south? See our Vietnam, Hoi An and Ho Chi Minh City briefings.

What travelers report

Paraphrased from TripAdvisor threads and linked so you can read them in full. None is dated, and bites vary with the season and whether you stay in the city or the countryside.

• Central Hanoi

  In a Hanoi mosquito thread, posters reported few or no bites in the city center, one saying they had never been bitten there in any season, and pointed to air-conditioned hotels and the drier months. TripAdvisor ↗

• Ninh Binh

  A reply said mosquitoes were not a problem during the day but DEET spray is useful in the evening, and that people often get bitten under restaurant tablecloths, where mosquitoes hide from the fans. TripAdvisor ↗

• Tam Coc homestay, Ninh Binh · September vs March-April

  In a question about a homestay, answers said bites were heavy during a September stay but almost absent on a March or April visit, and that the guesthouses provide nets for the beds. TripAdvisor ↗

If you're pregnant, talk to a healthcare provider before the trip, because Zika has circulated in Vietnam. And any fever during or within two weeks after your trip means a doctor visit, and you tell them you were in Vietnam. If you do get bitten, bitten in a dengue zone has the honest odds.

Traveler questions