Highly contagious norovirus to hit already flu-weary US

>>> the flu. the virus is widespread in 47 of 50 states . this morning there is a new concern. it's a new strain of the norovirus going around. and that's making people miserable in a whole different way. here's our chief medical editor, dr. nancy snyderman .

>> reporter: the flu is moving west. in this elementary school in dunk in, oklahoma, more than 10% of the students are out sick with influenza. staff has closed the school in order to clean everything.

>> one morning at school --

>> reporter: in san diego , this preschool staff is focusing on prevention by wiping down all the surfaces and teaching kids the best way to stay well.

>> this year, this season, this last two weeks has been very, very overwhelming almost because there's so many people sick.

>> reporter: influenza started with local outbreaks in october and then became widespread throughout the united states . the centers for disease control is reporting 37 children have died so far this flu season . young children and the elderly are most vulnerable. at the medical center in new york, the staff is working overtime, overwhelmed by flu and now something new.

>> this year in particular, there's an increase not just in the flu this time of year, but there's also a norovirus and a whooping cough outbreak going on simultaneously which is causing more people to present to the hospital looking for care.

>> reporter: norovirus causes severe naush avomiting, diarrhea, and abdominal pain. it's submitted when people don't wash their hands after using the bathroom, leaving the virus behind on surfaces and food.

>> it can stay alive for long periods of time and can be transmitted easily to anybody.

>> reporter: unlike influenza, there is no vaccine. so the best way to prevent norovirus infection, disinfect surfaces with bleach, and keep hands clean . bottom line, both of these illnesses serve as reminders, wash your hands. for "today," dr. nancy snyderman , nbc news, new york.