CHICAGO (CBS) — A private school in Lincoln Park was closed on Friday, after an outbreak of flu and a stomach bug left 20 percent of students and staff sick.

Officials will spend the day cleaning and disinfecting the Lincoln Park campus of the British International School of Chicago, after students and staff came down with both influenza and stomach flu.

Parents said they were told 20 percent of students and staff were sick. In a statement, the school said they canceled classes to prevent the spread of a stomach-related illness on campus.

School officials expected classes to resume at the Lincoln Park campus on Monday. The school’s South Loop campus was still open on Friday.

One woman stopped by the Lincoln Park campus Friday morning, clearly oblivious the school was closed. She tried to get in, knocked on the door, and waited before trying again.

A speech therapist also stopped by, not realizing the school was closed.

“It’s just better to get at the root of the problem before it starts escalating,” Lia Romeo said. “I think they managed really well. It was a quick decision, and having a close community with the parents and the school, that helps to take care of things in a quick fashion.”

Some parents said they had to scramble Thursday to find childcare after learning the school would be closed on Friday.

“A lot of our kids have been out sick lately, but to hear that a whole school is closed, it’s really kind of crazy. It’s been a big outbreak this year; a lot of cancellations because of it. So I hope everyone’s getting healthy,” Mary Cerrone said.

This has been one of the worst flu seasons in years. The U.S. Centers for Disease Control and Prevention recently estimated that 759 people died of flu-related illnesses between Oct. 7 and Dec. 23. Last year, only 322 people died during the same period due to the flu.America’s flu outbreak reached its worst point of season on Jan. 13, as the U.S. health officials say 32 states, Puerto Rico, and the New York City area were all designated “high activity” areas for the flu.

As of last week, the Chicago Department of Public Health reported 260 people had been treated at intensive care units this season due to flu-related complications.

Between Jan. 7 and Jan. 13, Loyola Medicine set a flu activity record with 190 confirmed cases. That was on the heels of a very busy December, when 357 cases were confirmed. The total since the start of flu season: 730 diagnosed flu cases.

However, Chicago Public Health Commissioner Dr. Julie Morita has said the worst of this year’s flu season likely is behind us, and things should get better from here.

In January, a pediatrician at Advocate Good Shepherd Hospital said getting vaccinated is still the best protection against the flu.

“The Centers for Disease Control confirm it’s not perfect protection, but it’s the best protection we have; and in addition to protecting yourself, it may protect somebody else who can’t receive the vaccine because of their age or other medical complications,” Dr. John Beckerman said.

While getting a flu shot might not prevent you from getting the flu, it should at least make the symptoms less severe, and make it less likely you’ll end up in the hospital.

“As sometimes happens different years, sometimes even people who’ve gotten the influenza vaccine still can come down with flu. The good news is those people tend not to be as sick as people who didn’t get the flu shot,” Beckerman said.