"The WHO China Country Office was informed of cases of pneumonia of unknown aetiology (unknown cause) detected in Wuhan City, Hubei" the W.H.O. wrote in a statement, days after receive the 31 December letter.
At the time the virus had 27 known cases and no deaths.
The W.H.O. advised authorities to keep a close watch, but not to introduce any specific measures for travellers or trade.
The coronavirus has since spread to most countries around the world, with over 25 million confirmed infections. At least 800,000 people have died with the virus.
Europe and the world have entered a new normal.
Economies are struggling to recover after weeks of lockdown and new restrictions on businesses that are reopening.
"Social distancing" has welcomed a new era in personal space, where authorities advise keep 1-metre distances between people.
And in some places, the wearing of face masks has become mandatory.
Euronews spoke with Marieke van der Werf from the European Centre for Disease Prevention and Control (ECDC) about the situation going forward