Christmas is coming but how can you celebrate it without giving the unwelcome gift of coronavirus?
Cosy rooms packed with people, chatting, laughing, even singing, and sharing food and drink for hours are the norm for the festive season.
Unfortunately, almost everything that’s great for lifting our spirits at Christmas is also ideal for fuelling the pandemic.
So here are the key questions to ask about any festivities.
How many people are invited?
No-one will be popular for saying this, but the evidence is clear - the larger the group, the greater the risk.
If it was summer and we could meet outside, where the virus gets dispersed in fresh air, it would be less of a problem. But it’s winter, so everyone’s inside.
And the more people who are involved, the greater the likelihood that someone may be a carrier of the virus - maybe without realising.
A study by Sage, the government’s science advisory panel, concludes that if you double the number of people getting together, you get a fourfold increase in the odds of infection.
It also matters how many different households are meeting - the fewer the safer - because the more different homes which are mixing, the greater the potential for the virus to spread.
Are you sharing food and drink?
Passing around dishes and bottles, encouraging everyone to tuck in, is one of the most natural of instincts at Christmas.
But the coronavirus can survive on surfaces, possibly for several hours, so plates and cutlery can become contaminated, which means you could be handing round the virus as well as the sprouts.
In the US, the official advice for this year’s Thanksgiving dinners is to break totally with tradition by asking guests to bring their own food and drinks.
It’s also recommended that you control who’s allowed in the kitchen, with one lucky person doing all the serving.
Can you keep the noise down?
Amid the excitement of reunions, it’s perfectly normal for voices to be raised.
Add a little alcohol, and maybe have a TV or music on as well, and things get even noisier.
But if someone is infected, the louder they speak, the more virus they release.
A lot of research shows that when voices are projected, people emit more tiny droplets of the kind that can carry the coronavirus.
That’s why for Thanksgiving gatherings, the US government advises: “Encourage guests to avoid singing or shouting, especially indoors.
“Keep music levels down so people don’t have to shout or speak loudly to be heard.”
Maybe the safest option is to hum Silent Night.
How long are you together for?
Popping in for a quick visit is safer than lingering over dinner for several hours.
Researchers say an event’s duration has a big impact on the infection risk.
In March, more than 50 members of a choir in the US were confirmed or suspected of being infected, after a two-and-a-half-hour rehearsal session.
Scientists reckoned that if it had lasted less than an hour, the number of infections would have been reduced by more than half.
Prof Cath Noakes, one of the study’s authors, says the problem is that tiny particles carrying the virus, known as aerosols, can accumulate in the air.
“There is growing evidence that if you’re in a poorly-ventilated space for a long period of time with people who are infected, you may breathe in those aerosols and that might be one of the routes of infection,” she said.
Are the windows open?
The obvious answer is: “Of course not, it’s too cold outside.”
But fresh air dilutes any virus that might be lingering in a crowded room.
A Sage report says infection risks can be increased by four times without proper ventilation.
And in this context, “ventilation” doesn’t mean having fans blowing the air around, but a flow of air from outside.
And if people feel too cold? Wear another layer.
So is there a safe way to celebrate?
According to Prof Noakes, people must dream up creative new options for Christmas
That could range from meeting virtually on Zoom, going for a walk, braving the weather for a picnic, or even delaying big gatherings until next summer.
If you are planning a meal indoors, she says, make sure you keep everyone as far apart as possible and be careful to keep everything clean.
Also try to avoid having people from different households sitting opposite each other because speaking face-to-face is a route of transmission.
But is any of this feasible?
Any social setting increases the risk of infection, says Prof Noakes, and we will have to compromise, reduce our contacts with people and do things in a different way.
“The virus doesn’t know it’s Christmas,” she says. “It’s just a virus and it thrives on human contact.”