Southeast Asia is in peak season for Zika and dengue transmission. The spread of Zika in the region has been slower than in the Americas, though over 1200 cases of Zika have been reported across the Philippines, Thailand, Vietnam, and Singapore, and more countries continue to report new infections, including Malaysia, Cambodia, and Indonesia. The slower spread of disease may be due to preexisting immunity – i.e. the region has experienced “silent” transmission of Zika virus in the past – or under-reporting, as Zika symptoms can be clinically mistaken for the much more common dengue fever.
Seasonally, the second half of the year is a time of concern for the spread of Zika in these countries. Dengue, which is spread by the same mosquito species, peaks significantly in this time of year with some variation. Singapore, for example, has had unusual dengue transmission in 2016 as more cases were reported in the first half of the year. Thailand and the Philippines, though, have reported tens of thousands of cases of dengue so far in 2016 and are still in peak season. This indicates ongoing potential for Zika spread, as well.
Based on current reporting, Zika transmission in SE Asia is highly unlikely to swell to the size of the outbreak in the Americas in 2016. However, given the risk of severe neurological disorders and potential under-reporting, people living in or traveling to Thailand, the Philippines, and Vietnam should be cautious in the month ahead. This means wearing mosquito repellent in areas with active dengue or Zika transmission and clearing out mosquito breeding spots. Pregnant women should follow the national health recommendations.