The UN agency said people should not underestimate “the importance of your decisions” and encouraged extra precaution for holiday gatherings, even within the family.
If possible, the WHO said celebrations should be held outdoors and “participants should wear masks and maintain physical distancing.”
For indoor festivities, the WHO said limiting the number of guests and ensuring good ventilation were key to reducing the risk of infection.
“It may feel awkward to wear masks and practise physical distancing when around friends and family, but doing so contributes significantly to ensuring that everyone remains safe and healthy,” the health agency said in a statement.
The plea came as the agency noted that “Covid-19 transmission across the European region remains widespread and intense,” even though some “fragile progress” had been made.
“There is a high risk of further resurgence in the first weeks and months of 2021, and we will need to work together if we are to succeed in preventing it,” WHO Europe said.
The WHO's European Region comprises 53 countries and includes Russia and several countries in Central Asia, a region that has registered more than 22 million cases of the new coronavirus and close to 500,000 deaths.
In the last seven days, nearly 1.7 million new cases have been recorded, as well as more than 34,500 deaths.
As a second wave of the novel coronavirus is sweeping over the continent, many countries have once again introduced tough measures to curb the spread.
On Wednesday, several new measures were imposed, including the closure of non-essential shops in Germany and pubs and restaurants in Britain.