Flu is hitting a second peak in the U.S. this season. A doctor shares what to know.

For a second time this season, the flu is surging, with at least 41 states reporting high or very high levels of the virus. 

Emergency room visits for the virus have shot up nearly 30% this week compared to the week before. The increase in cases has led to temporary school closures in places around the country, including in Texas and Tennessee.

Dr. Rabia de Latour, a gastroenterologist at NYU Langone Health, told "CBS Mornings Plus" Thursday that recent data show there have been more than 20 million cases, 250,000 hospitalizations and over 11,000 deaths so far this flu season.