One thing’s for sure: “We are going to see a spike in cases. And that’s because Omicron is incredibly transmissible, and you know, we have to be prepared for that,” as Surgeon General Vivek Murthy said on CNN. Make that two things are for sure: Murthy continued, “But there will be a stark difference between the experience of those who are vaccinated and boosted versus those who are unvaccinated.”

If you’re vaccinated, why should you get boosted? The CDC’s data collection program is struggling to keep up, but check out these numbers:

A big part of what an omicron-plus-holidays spike will do to the country, though, lies in how much it overloads health care systems—something that could affect not just COVID-19 patients, but anyone who needs any kind of care from an overwhelmed system. If you get in a car accident or have a heart attack, you are in direct competition with COVID-19 patients for hospital beds and doctors and nurses. 

The scientific jury is still very much out on how virulent omicron is, with conflicting studies suggesting either that omicron might cause milder symptoms or that it is no less severe than previous versions. (Guess which one of those is getting more attention.) But what is fairly clear is that omicron travels fast. Really fast. “Estimates for this exposure-to-symptom gap, called the incubation period, clocked in at about five days for Alpha and four days for Delta,” writes Katherine Wu at The Atlantic. “Now word has it that the newest kid on the pandemic block, Omicron, may have ratcheted it down to as little as three.”

That means that that PCR test you took 72 hours ago is way out of date by now. Rapid tests, though less sensitive than PCR tests, may be a better bet for staying on top of a quickly moving virus—if you can both afford and locate them. Even rapid tests may fall behind reality between, say, a Christmas Eve gathering and a Christmas Day one, unless you have enough of them to take regularly through the holidays. And accessing tests is becoming a problem as the combination of holiday travel and omicron anxiety combine to dramatically increase demand.

The holidays are a time when young, healthy people gather with their elderly family members for whom COVID-19 poses a bigger threat. They’re times when vaccinated and unvaccinated family members may gather. If you care about slowing the spread of the coronavirus at a moment when it appears to be accelerating to blazing speed, the right mitigation tactic is … as many of them as you can put together.

Vaccination and boosters are key. Testing, if you can get it, is hugely important. Wearing masks wherever it is possible to do so continues to be a good practice. Limiting the size of your events as much as possible—with the recognition that many people gave up a family Christmas last year and simply will not do so again this year—is very much worth it. If you live in a place with weather that allows outdoor socializing at this time of year, move as much of your celebration outdoors as you can. If you have access to air purifiers or ways to improve ventilation where you’re gathering, use those. And don’t be surprised—but do be responsible in your behavior—if you get a breakthrough infection.