The holiday season: A time for family, feasting, and for rampant strains of the flu virus to infect you and your loved ones.

Flu cases in New York started spiking earlier than usual this year. As New Yorkers travel to and from the city, attend parties, and visit family and friends, health officials are urging people to take precautions against a strain that seems to be tearing through the region.

Here’s what to know about the virus, vaccination rates and how to stay healthy this holiday season.

What’s new about this year’s flu?

The dominant flu virus that’s currently infecting people across the country is a relative of the common H3N2 strain. But experts say this variant, called subclade K, has a number of mutations that don’t respond as well to vaccines.

“Symptom-wise, [there’s] nothing that we know that's different about this virus outside of the fact that it's just going to be able to infect more people and therefore we'll see more cases,” said Andy Pekosz, a virologist and professor of microbiology at Johns Hopkins University's Bloomberg School of Public Health.

Still, Pekosz encouraged people to get vaccinated to prevent the most severe symptoms of the disease, and to guard against some of the other strains in circulation.

As of mid-November, 3.4 million New Yorkers statewide had received their flu shots — about 5% fewer than had been vaccinated by that time last year, according to the state Department of Health.

Schools, kids on the front line

The virus is also coursing its way through city schools.

In New York City, nearly 500,000 children have received flu shots so far this season, representing a 6.5% drop compared to the same period last year, according to the city health department.

Parents have been telling Gothamist anecdotally that classrooms have been half-empty this week but the city Department of Education couldn’t immediately say if there’s been a significant, systemwide drop in attendance. Attendance at New York City schools was at 85% Thursday.

Poly Prep Country Day School closed its Dyker Heights campus on Dec. 10 and 11 out of “an abundance of caution” after about a third of the student body was absent or sent home with flu-like symptoms, according to Jennifer Slomack, the school’s senior director of engagement and communications.

“The two-day closure allowed students time to rest and recover while we simultaneously did an intensive disinfection of hard surfaces and UV sanitizing through our forced-air HVAC systems,” she said. Attendance numbers rebounded after the school reopened on Dec. 12.

Leslie Pennypacker, executive director of Tribeca Pediatrics, said her staff has reported more than 2,000 positive flu cases — a “significant” increase — in the last two weeks among children coming into their 50 offices across the NYC metro area.