Omicron makes people sick faster. Here’s what else you need to know for New Year's weekend

This would be a good New Year's to spend at home.

Omicron makes people sick faster than earlier variants, according to a study released Tuesday by the Centers for Disease Control and Prevention that confirms what many have already observed.

Although most cases of omicron appear to be relatively mild, people generally get COVID-19 symptoms three days after being exposed to the virus, rather than about four days with delta and five or longer with the original virus, the study concludes.

People are probably contagious sooner after exposure – and maybe even before they test positive for infection.

All of which makes for terrible timing to come together in large groups to ring in a new year. Jacob Lemieux, an infectious disease expert at Massachusetts General Hospital, recommended saving the parties for later.

"The thing to do is to postpone when the force of infection is so high and look for a time in the future when it's safer to do these things," he said. "In a few weeks, the situation may be substantially better."

Cases have been rising sharply since Thanksgiving, according to the CDC, and more than 85% of U.S. counties meet criteria for "high" COVID-19 transmission, USA TODAY analysis of Johns Hopkins University data shows.

The new CDC study focused on one family in Nebraska, reinfected with omicron after catching COVID-19 last year. One of the five family members was vaccinated. All five had similar or milder symptoms with their new infections, the study found.

It's not clear whether the family members were reinfected because their immunity faded over the year between infections, whether omicron is better at getting around immunity from infections or both.

The data fits with what doctors are seeing with omicron: People are coming down with symptoms faster.

"We're seeing people test positive as early as Day 2," said Dr. Daniel Griffin, chief of infectious diseases for ProHealth Care, which provides services at 300 locations in and around New York City.

In a Saturday night "Santa-con" convention in New York City in mid-December, he said, people who attended started to test positive on Monday, and more on Tuesday.

Symptoms in some people seem to come before they test positive, Griffin said. "Do the rapid (test) today, but do it again tomorrow," he said.

If widespread, this could be good news. Many other viruses are far easier to contain than SARS-CoV-2 has been because people feel sick before they are contagious, so they can isolate themselves.

"That could be huge," Griffin said, "Then we really could go back to what we did with flu: Don't go back to work or school if you're feeling sick."

Here are answers to some other common questions you might have about omicron and testing:

How does omicron affect children?

It's still unclear whether omicron is more likely to make children sick than earlier variants. Children under 5 are not eligible for vaccination. "We keep seeing upticks in kids," perhaps because they're unvaccinated, Pardis Sabeti, a computational geneticist, said Monday on a call with reporters. "We should protect those who can't protect themselves, because we don't know what a virus can do."

In Houston, Texas Children's Hospital follows children to see whether omicron affects them differently than previous variants or whether there are different risk factors for severe disease, said James Versalovic, the hospital's pathologist in chief. Staff will gather data on the vaccination status of children hospitalized with COVID-19.

"We will be watching and monitoring during the days and weeks ahead with the new variant," he said. "At this point, we just expect to see more of the same."

How soon after exposure can a test determine if I’m contagious?

How quickly people will be contagious after infection is tough to predict, said Sabeti, who works for the Broad Institute of MIT and Harvard, a genetics research center. It depends on an individual's viral load, as well as the specific variant.

Omicron moves so quickly, she said, that it's possible to test negative in the morning but be positive by the afternoon or evening. "I don't feel as if we know enough about the exact dynamics of when you test positive and how likely you are to then spread it," she said. Diagnostic tests are helpful, but they're not foolproof.

The best way to ensure protection, she said, is by layering protection: testing, masking and getting vaccinated.

There is an association between having symptoms and being contagious, she said, but it's not a perfect correlation. "We've seen plenty of people who are completely unaware, asymptomatic, but with screaming viral loads," she said. "And we've seen people who are symptomatic with very low viral loads."

What kind of tests can I get?

Molecular PCR tests, often administered at clinics, doctors’ offices, hospitals or large-scale testing sites, are more sensitive and can detect traces of the virus over a longer period during the course of an infection. These tests often require medical oversight, typically deliver results in a day or two and are more expensive, often costing $100 or more per test.

Rapid antigen tests can be taken at home, typically deliver results in about 15 minutes and don't require a lab. They're less expensive.

Although these tests are slightly less likely than PCR tests to detect the virus, advocates said they are accurate enough to detect the virus when a person is infectious and likely to pass it to others.

Anyone who tests positive on a home test should contact a doctor and may want to get a lab test to confirm the results.

Are home tests hard to find?

The two largest manufacturers, Abbott and Quidel, slowed production this spring as coronavirus cases dropped. The manufacturing cutbacks followed a CDC recommendation that vaccinated people did not need to get tested. The CDC reversed its guideline as more breakthrough cases emerged.

Home test shortages surfaced this summer when the delta variant increased cases and more people sought testing. Although the Food and Drug Administration has given emergency use authorization to more than a dozen home test manufacturers, home tests are frequently sold out at major retailers.

How sick am I likely to get if infected?

Omicron appears to cause less severe disease than earlier variants, particularly among people who have been vaccinated or previously infected.

But it's also causing more "breakthrough" infections in those who thought they were protected by vaccination or infection, and people with weakened immune systems remain at extra risk, experts said.

What if I'm traveling or going out for New Year's?

Because omicron spreads so quickly and efficiently, the odds are greater that you will come into contact with the virus. If you are committed to attending a gathering, get vaccinated and boosted and encourage friends and family to do the same.

"That's probably not going to prevent people from getting this virus, but I would much rather have a mild cold than be worried about prospects of going to a hospital," said Jennifer Nuzzo, an epidemiologist and senior scholar at the Johns Hopkins Center for Health Security.

Boosters usually take at least a week to provide protection, and the first doses, separated by three or four weeks, take about six weeks to reach full protection, data shows.

Experts recommend people get tested right before a gathering instead of a few days beforehand. One example might be to administer rapid tests in a car before entering someone's house. Although home antigen tests are not perfect, "perfect is not the goal. We need everyone to be a bit better," Nuzzo said.

If you live in a warm-weather state, try to spend time outdoors. Once inside, open windows to improve air flow and wear a mask as much as possible.

People should be especially cautious in crowded airports before boarding a plane, Nuzzo said. "I'm always much more worried about the airports than I am about the plane."

No strategy is perfect and people should make decisions based on their health status and the health of their friends and families, said Dr. Michael Mina, an infectious disease expert and former Harvard professor who serves as chief science officer of the testing company eMed. Frequently using home tests will give people better odds of keeping themselves and others healthy, he said.

"We're not looking for perfect. We're looking for the greatest risk reduction strategies," Mina said. "Perfect is staying holed up in your room and not moving. But (nearly) two years into this, it's no longer what most people are willing or even should be considering."

Contributing: Mike Stucka

Contact Karen Weintraub at kweintraub@usatoday.com.

Health and patient safety coverage at USA TODAY is made possible in part by a grant from the Masimo Foundation for Ethics, Innovation and Competition in Healthcare. The Masimo Foundation does not provide editorial input.

This article originally appeared on USA TODAY: Omicron makes people sick faster. Here's what to know this New Year's.