WHO certified the tropical island nation of having eliminated malaria - a life-threatening disease caused by mosquito bites.
"Sri Lanka's achievement is truly remarkable. In the mid 20th century it was among the most malaria affected countries," WHO Regional Director Dr Poonam Khetrapal Singh said.
Sri Lanka is the second country in the WHO South-East Asia Region to eliminate malaria after Maldives.
The Regional Committee has eleven member countries: Bangladesh, Bhutan, Democratic Peoples' Republic of Korea, India, Indonesia, Maldives, Myanmar, Nepal, Sri Lanka, Thailand and Timor Leste. It meets annually to discuss its programmes and budget which is hosted by a member country.
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After malaria cases soared in the 1970s and 80s, the country's anti-malaria campaign in the 1990s adjusted its strategy to intensively target the parasite in addition to targeting the mosquito.
The decision to declare Sri Lanka malaria-free was taken after WHO's East Asia region's annual committee meeting.
The five-day WHO event from September 5 to September 9 will also help to showcase Sri Lanka's achievements in the health sector and the progress the country has made in socio-economic development while highlighting its tourism potential, Sri Lankan officials said.