Why dengue fever numbers have plummeted in Southeast Asia this year

Data from the World Health Organization (WHO) suggests that several countries are enjoying vastly improved dengue fever situations this year, including Malaysia, Thailand, Indonesia, the Philippines, Cambodia and Laos.

Most of those countries have seen reported case drop by around 70%.

Other countries, including Singapore and Vietnam are experiencing dengue cases on par with seasonal expectations, according to WHO.

Dengue fever is a potentially deadly disease spread by infected Aedes aegypti mosquitoes and is the world’s most common mosquito-borne virus.

But during the second year of Covid-19, underreporting from strained medical systems and extensive social lockdowns could explain why many Southeast Asian countries have recorded substantially fewer cases of dengue fever in 2021 than previous years.

Some experts, however, say that while there is consensus that 2021 is not a bad year for dengue fever infections in the region, especially compared to 2019, the statistics may not necessarily reflect the truth.

“People aren’t reporting fever as they would normally, because of Covid,” said Martin Hibberd, a professor of emerging infectious diseases at the London School of Hygiene and Tropical Medicine.

“Also, health centres are not in their normal responsive mode. Their priorities are elsewhere and they’re not testing as much as usual, so the numbers reported must be less,” he told CNA.

A WHO spokesman did not identify any clear reasons for why dengue cases are declining but said they could include more proactive vector control, stronger national surveillance systems and better communication with the community as well as the overwhelming demands of handling the Covid-19 pandemic.

“There is also a hesitancy to seek medical care at facilities due to concerns of possible exposure to Covid-19 patients,” the spokesman added.

When the Covid-19 pandemic hit, many experts said that social lockdowns and people spending more time at home would result in an uptick of dengue.

“Mosquitoes live in the house, and we thought if more people stay at home there would be more dengue but that’s clearly not the case,” Hibberd said. “It could be that outside of home plays a more important part in dengue transmission than we thought.”

WHO has implored countries to build up their capacity to handle the disease.

The cyclical nature of dengue fever means a more serious outbreak is expected within the next two or three years.