The world health organisation day is –
World health organization (WHO) 

The WHO is a specialized non-political health agency with headquarter at Geneva.
In 1946, the constitution was drafted by the "Technical preparatory committee “under the chairmanship of Rene sand and was approved in the same year by an international health conference of 51 nations in New York.
The constitution came into force on 7th April 1948, which is celebrated every year as world health day.
7th April
21st May
2nd August
31st December