From skiing to shopping to testing, here’s what you need to know to stay safe during Omicron

As scientists race to understand this new wave of the pandemic, information is proliferating almost as fast as the virus itself, and it can be hard to keep up. Here’s advice from experts on how to apply the latest news about Omicron to your daily life:

Omicron is by far the most infectious coronavirus variant and one of the fastest-spreading viruses ever known. First detected in late November, it traveled the world within one month, infecting millions. Some experts have called it the second-most infectious disease after measles, while one doctor calculated that it transmits even faster than measles.

What happened in Massachusetts illustrates Omicron’s lightning pace. Researchers at the Broad Institute of MIT and Harvard found strong evidence of Omicron in 45 percent of samples taken Dec. 13 through 16. By the next week, that was up to 80 percent, and has now reached 95 percent.

The answer to all these questions is: It depends. “There are gradations of safe,” said Dr. Megan L. Ranney, an emergency physician and academic dean for the Brown University School of Public Health.

You have to consider your own level of protection, the setting you’re heading to, and whether there are vulnerable people in your household. If you are vaccinated and have received a booster shot, you’re highly unlikely to get seriously ill. But you could still catch COVID-19 and spread it to others.

Ranney shops for groceries, but with a high-quality mask (see below for details). She doesn’t eat at restaurants indoors, because that requires removing the mask. She lets her kids, who are vaccinated, play indoor sports, but only in places with good ventilation and where everyone is masked. “But it’s not risk-free,” she notes.

Eve Wittenberg, senior research scientist in the Center for Health Decision Science at the Harvard T.H. Chan School of Public Health, recommends trying to keep it simple.

Are you vaccinated, boosted, and wearing a high-quality mask? Are you free of any medical conditions that put you at high risk? Can the same be said about the people you live with?

If the answer is yes to all these questions, then sure, go to the grocery store — your risk is low, she said.

But if there are unvaccinated children in your household or you live with an elderly or immunocompromised person, you may need an extra layer of protection. You might want to opt for curbside pickup, to play it safe.

Another important consideration is the value of the activity you’re considering, Wittenberg said. Some things are worth the risk, such as visiting family for the holidays.

Over the course of each week, pick and choose among the risks you take, and “take the risks where there is a huge payoff,” Wittenberg advises. If going to the grocery store is really important to you, maybe order online from CVS. “It’s a balancing act of . . . making decisions between which are the ones that have high benefit and which ones you can do without,” she said.

For some people, online decision apps can be helpful. Ranney recommends mycovidrisk.app, developed by the Brown-Lifespan Center for Digital Health, which she founded. The program, which has been adjusted to account for Omicron’s higher transmissibility, asks a few questions about the activity you’re planning and rates its risk level. Then it invites you to lower your risk by answering such questions as whether you and the people you’re with will be vaccinated and masked. The app then displays a dial showing whether your risk is low, moderate, or high.

Wittenberg thinks such apps are “nifty, fun, good in principle” but cautions that some people may find them stressful. “It does all the math for you, but it makes you hyperaware of the 72 factors [that will] decide whether you’re going to die next week,” she said. And these apps don’t help with spur-of-the-moment decisions, such as whether to run into a store to grab a couple of items.

The transmission almost surely didn’t happen on the slopes. As with parades and the Sturgis motorcycle rally, the indoor activities that accompany these events are where the virus is most likely to spread.

Ranney suspects that gatherings in the ski lodge and after-ski parties are to blame. “You come off a slope, go into the lodge, get a cup of hot chocolate, get a beer,” she said. Those are activities that can’t happen while wearing a mask. “There’s not something magical about being in a place of eating that makes the virus stop transmitting,” Ranney said.

All variants of the coronavirus transmit in the same way, by traveling through the air, and masks can keep the virus at bay. But the difference with Omicron is that infected people carry higher quantities of the virus, and it attaches to the mucus membranes more readily. For better protection, Ranney is urging people to “up their mask game” by wearing medical-grade KF94, KN95, or N95 masks.

“I would rather that someone wear a surgical mask or cloth mask than no mask,” she said. But to protect against Omicron, a tougher barrier is preferable. Unfortunately there are many poor-quality knock-offs on the market, so Ranney recommends ordering through Projectn95.com, a nonprofit that sells medical-grade masks to consumers.

Yes, but with some caveats. The Food and Drug Administration has been evaluating antigen tests and reported last week, “Early data suggests that antigen tests do detect the Omicron variant but may have reduced sensitivity.”

But new research suggests these tests may not detect coronavirus early in the course of infection. Experts emphasize that the tests are still worth using, but if you’ve been exposed to someone with COVID-19 or have symptoms, don’t assume that a negative test gives you a free pass. You may want to stay home and test again in a day or two.

Sadly, it appears so. Vaccinated people who have had mild, breakthrough cases of COVID-19 have developed long COVID, a syndrome in which symptoms such as memory loss and fatigue continue for months after a COVID infection. But studies differ on whether or not vaccines reduce the likelihood of developing long COVID.

Dr. Jason H. Maley, director of Beth Israel Medical Center’s Critical Illness and COVID-19 Survivorship Program, said his clinic has “certainly continued to see long COVID with breakthrough infections and it’s become clear that unfortunately patients are at risk of long COVID in that scenario.”

With Omicron’s fast rise and ability to infect vaccinated people, the numbers of people with long COVID could soar.

“We anticipate that long COVID will be similarly common among people infected with Omicron,” Maley said in an e-mail. “We don’t have firm data on this because it’s just too early in the course of the current Omicron surge to know long-term outcomes.”

The risk of long COVID is another reason why vaccinated people should continue to wear masks and take other precautions. Even though Omicron appears to produce milder illness than other variants, COVID-19 remains a disease you don’t want to get.

Felice J. Freyer can be reached at felice.freyer@globe.com. Follow her @felicejfreyer.