Yap's 2007 Zika outbreak made history. Low-level dengue is what to plan for now.

Are there mosquitoes in Micronesia? Yes. The Federated States of Micronesia has day-biting Aedes mosquitoes and dengue that circulates at low levels, and in 2007 Yap had the first Zika outbreak ever detected outside Africa and Asia. There is no malaria, so for a Chuuk wreck-diving trip or a visit to Pohnpei's Nan Madol, the routine is repellent by day and a sealed room at night.

Yap's place in Zika history

In April 2007, doctors on Yap noticed an outbreak of rash, conjunctivitis and joint pain. A rapid test first pointed to dengue. In June, CDC laboratory testing identified Zika virus, the first Zika outbreak detected outside Africa and Asia, as CDC's Emerging Infectious Diseases journal reported in 2008 and 2009. Aedes hensilii was the main mosquito on Yap during the outbreak, though no virus was found in mosquitoes, and a medical volunteer fell ill with Zika after returning to the United States.

Today CDC lists the country among areas with current or past Zika transmission and no outbreak. For those areas it tells pregnant travelers to "Talk to a health care provider about potential risks. If you decide to travel, prevent mosquito bites and sexual exposure to Zika."

Dengue, Chuuk and the wreck divers

Dengue circulates at low levels with occasional clusters, and dengue cases were confirmed in Chuuk in early 2026, regional Pacific health alerts reported. The World Health Organization's Pacific surveillance showed small rises in weekly dengue-like illness reports in May and early June 2026, and its charts have no FSM figures after early June. There is no CDC travel notice, and the country isn't on CDC's global dengue list.

Chuuk Lagoon's WWII wrecks keep divers on the water through the day, so the bites wait on land. On Weno, rooms with louvered jalousie windows have a reputation for letting mosquitoes in at night. Keep them shut, run the air conditioning and use a bed net if the room is open to the air. On Pohnpei, the waterfall hikes and the mangrove channels around Nan Madol's basalt ruins tend to be buggier, so spray before you set out and wear light long sleeves. Everywhere, put repellent on over sunscreen in the morning, reapply after diving and again from late afternoon. Our dengue & Zika routine has the schedule.

CDC recommends no malaria medicine and no yellow fever vaccine, and the vaccine isn't required for entry. Leptospirosis is on CDC's page, so avoid floodwater and wading in fresh water or mud.

When to go

Rain falls all year, and Pohnpei has a reputation as one of the wettest places on Earth. WHO's five-year baseline for FSM usually peaks around September, with a smaller rise in August, and roughly January to July has been quieter. In 2026 the highest weekly counts came in scattered weeks from late February to early June. Divers come in every month, and the routine is the same in all of them.

Where you're going

How the four states compare across the year.

Visiting Guam or Palau on the same trip? Our Guam and Palau briefings cover both, and our Marshall Islands briefing covers the 2026 outbreak in Majuro.

One rule outlasts the trip. Any fever during or after your trip means a doctor visit, and you tell them you were in Micronesia and which islands, especially with headache, rash or body aches in the two weeks after you get home. Our after-bites guide covers the warning signs.

Traveler questions