More than nine months into the coronavirus pandemic, the weather is getting cold. Thanksgiving and Christmas are on the horizon. Naturally, many Americans will be tempted to mingle indoors with friends and family.

Forming "social bubbles" - small groups that agree to spend time together indoors, exclusively with each other - may be the safest way to do that.

But public-health experts say the approach is still somewhat risky, given that the US is seeing record-high numbers of new coronavirus cases. The tighter the bubble group's restrictions, however, the more that risk goes down.

"You have to remember that there are no zero-risk scenarios and most people's bubbles are bigger than they think they are," Dr. Anne Rimoin, an epidemiology professor at UCLA's Fielding School of Public Health, told Business Insider.

"You will need to trust the people you are 'bubbling' with and that everyone will be honest and open about any exposures that they have had - or that the people around them have had."

Business Insider asked five infectious-disease experts for their advice on creating a safe social bubble, or "pod". Some recommendations were more conservative than others, but all experts agreed on a few key things to avoid.

Tips for a safe bubble

On a scale of one to 10, the risk of forming a social bubble is "everywhere from two to nine," depending how people in the bubble behave, Dr. Murray Cohen, a retired CDC epidemiologist and medical advisor for Wello, told Business Insider.

But there are some strategies for keeping that risk low:

1. Keep your bubble small.

In an ideal scenario, experts recommend avoiding close, indoor contact with anyone outside your household. If you do decide to expand your bubble, as few households as possible is still best.

"You should look at the local guidelines on how many households or number of people are allowed to get together," Rimoin said.

"For example, in Los Angeles County, the Department of Health limits three households getting together."

Saskia Popescu, an infectious-disease expert at George Mason University, also recommended teaming up with only one or two other households maximum. Other experts said a good rule of thumb is to cap the group at around six to 10 people.

Lisa Lee, an epidemiologist at Virginia Tech, said there are six people in her "pandemic pod", including her.

But bubbles can be larger if everyone inside follows rigorous safety measures like routine testing and limited outside activities.

"The NBA very effectively had a social bubble of all 30 teams," Cohen said. "It's really more a matter of what you do inside and outside the bubble than it is how big the bubble is."

2. Quarantine for two weeks beforehand.

Coronavirus symptoms can take up to 14 days to manifest after a person gets infected, so experts recommended waiting two weeks before forming a bubble to make sure all members are symptom-free. During that time, the entire group should avoid non-essential activities.

"Everyone needs to be very careful in that two weeks before they go into that group to try to minimise the risk," Scott Weisenberg, an infectious-disease specialist at NYU Langone Health, told Business Insider.

Some experts said it would be helpful to make sure everyone in the bubble has tested negative before coming together, but they also cautioned that testing could provide a false sense of security. If members venture out in public in-between getting tested and joining the group, there's still a chance they could be infected.

Cohen also recognised that it's still difficult for many Americans to get a coronavirus test.

"Since testing is so spotty right now, I don't think that makes a difference," he said. "What you're really going to work on is symptoms."

3. Keep the windows open.

Outdoor gatherings are generally safer than indoor ones, but they're less feasible during the winter. The next-best option, experts said, is keeping a room well-ventilated.

"If people have to be indoors, keeping the window open and trying to mimic an outdoor environment as much as possible can lower the risk," Weisenberg said.

4. Masks and social distancing are still advised.

Experts widely agree that masks and social distancing should still be enforced inside a bubble. Ideally, people should remain 6 feet (2 metres) apart, though 4 feet (1 metre) of separation in a cramped space is still better than nothing, Weisenberg said.

Wearing masks, even just some of the time, can help lower the group's risk.

"The bubble is just a strategy to try to reduce overall exposures and let people have some social contact, but it doesn't mean we can let our guard down," Weisenberg said.

"All it takes is one person in that group to have an exposure."

Risks to avoid in your pod

Some Americans should steer clear of social bubbles due to their age, profession, or pre-existing conditions. Here's what experts said won't work when forming a group.

1. Don't mingle with vulnerable individuals.

Since bubbles still carry some risk, experts don't recommend forming them with elderly people (typically those over 60), pregnant women, or people with pre-existing health problems, including obesity, high blood pressure, and diabetes.

"Always be mindful: It's not perfect. You might slip up," Cohen said. "So for God's sake, don't have my 94-year-old mother in there."

2. Bubbles shouldn't include teachers, students, or essential workers.

A bubble effectively "pops" if even one group member spends time indoors with other people. That includes teachers and students who have resumed in-person school. People should also be wary of pairing up with essential workers, who are more likely to face daily exposure to the virus.

"If you've got people going back to offices or workplaces of any kind, they have just violated whatever a social bubble is," Cohen said.

3. Steer clear of indoor dining.

Experts still caution against most indoor dining, whether as individuals or as a pod.

"If I go to a restaurant and I'm not wearing a mask while I'm eating, even if I'm more than 6 feet away, there's going to be some risk of me getting the virus from people around me," Weisenberg said.

4. Avoid multiple, overlapping bubbles.

Experts had mixed takes on whether two social bubbles could expand to form one larger bubble. If people are being extra careful, Cohen said, it's possible that all members could mingle indoors.

"It's almost more like a Venn diagram," Cohen said.

If two bubbles are virus-free, then the combined group likely won't have any cases, either. In general, though, the safest option is to limit interactions to just your immediate group.

"The critical piece is that you don't bubble with someone, who then bubbles with someone, who then bubbles with someone," Popescu said.

"That's always my concern, it really needs to be someone that you trust."

Hilary Brueck contributed reporting.

This article was originally published by Business Insider.

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