As it looks now, all hypotheses must remain on the table, including zoonotic spread and a leak from a laboratory, said WHO chief Tedros Adhanom Ghebreyesus at a press conference.
Much of the information requested, mainly from China, has been lacking.
Despite repeated requests, China has not provided access to hundreds of virus sequences from individuals with covid-19 early in the pandemic, more details from animals sold on markets in Wuhan and information on measures and safety in laboratories, he added.
WHO has simultaneously requested access to reports prepared around the world regarding the origin of the pandemic.
The purpose of the work, which continues, has been to try to prevent similar pandemics in the future.
The pandemic killed an estimated 20 million people worldwide. The first cases were discovered in Wuhan, China in 2019, and in March 2020, WHO characterized the outbreak as a pandemic.
WHO also notes that there is no evidence that the preservative Thimerosal, used in vaccines, would be harmful. Health authorities in the USA, appointed by the Minister of Health and vaccine skeptic Robert F Kennedy, have recently questioned the use of the agent.
