Europeans planning to celebrate Christmas, New Year's and winter holidays in coming weeks with family and friends were advised to wear a face mask, a European health agency said.
The World Health Organization's (WHO) European office issued the advice on Wednesday as part of efforts to reduce the risk of spreading Covid-19.
"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," the Copenhagen-based agency said.
Where possible, gatherings should be held outside and participants should also maintain physical distancing.
If a gathering is held indoors, "limiting group size and ensuring good ventilation to reduce exposure risk are key," it added.
Wearing a mask might feel "awkward" when among friends or family but it "contributes significantly to ensuring that everyone remains safe and healthy," it said.
Other advice was to avoid crowding, for instance at after-ski events at ski resorts or during travel or public transport hubs.
Authorities and communities were advised to consider "postponing, limiting or cancelling mass gatherings" including religious processions, markets and church services, especially where transmission rates were high.
The WHO European region groups 53 countries.