The flu virus continues to hold its grip on New Jersey as new confirmed cases of the illness pop up.

“Super Bowl Sunday we evaluated close to 60 patient samples and about half of those patient samples were positive for influenza,” says Hackensack University Medical Center clinical director Dr. Gary Munk.

The New Jersey Health Department says that the flu is widespread across the Garden State with high activity in all 21 counties.

Pediatrician Julia Piwoz says that parents need to be vigilant because children are especially vulnerable to the illness.

“People go to school before they know they’re sick,” she says. “They may be contagious before they have symptoms.”

At least one New Jersey school district had to close Monday due to an increase in the illness. All three of Branchburg’s schools were closed because there were too many sick bus drivers.

There have been about 5,000 confirmed cases of the flu in New Jersey this year.

Health officials say that the flu vaccine is less than 40 percent effective against the worst strain of the virus this year. Doctors say that people should still get the shot because it does offer some protection and can ease symptoms.

New Jersey has already seen one fatal case of the flu – a 4-year-old girl died in December from complications.