Flu season was off to an early \u2014 and vicious \u2014 start this year, with [hospitalizations](https:\/\/www.cbc.ca\/news\/health\/pediatric-flu-visits-2025-9.7003201) up across the country. CHEO, eastern Ontario’s children’s hospital in Ottawa, says it has seen \u201cunprecedented\u201d numbers of sick patients lately, with nearly 300 young adults visiting the emergency department in a single day, CHEO\u2019s vice-president of acute care services, Karen Macauley, [told CBC News](https:\/\/www.cbc.ca\/news\/health\/pediatric-flu-visits-2025-9.7003201).<\/p>\n
Across all Ontario hospitals, ICU admissions jumped 127 per cent<\/a> in a week, the Ontario Hospital Association said on December 17.<\/p>\n What does this have to do with the weather?<\/p>\n \u201cMany viruses, including rhinovirus \u2013 the usual culprit for the common cold \u2013 influenza, and SARS-CoV-2, the virus that causes COVID-19, remain infectious longer and replicate faster in colder temperatures and at lower humidity levels,\u201d public health nurse Libby Richards explained in 2024<\/a>.<\/p>\n \u201cThis, coupled with the fact that people spend more time indoors and in close contact with others during cold weather, are common reasons that germs are more likely to spread.\u201d<\/p>\n Richards says cold weather can change the outer membrane<\/a> of the influenza virus, giving it a more solid and rubbery coating that makes person-to-person transmission easier.<\/p>\n \u201cIt\u2019s not just cold winter air that causes a problem,\u201d she says<\/a>.<\/p>\n \u201cAir that is dry in addition to cold has been linked to flu outbreaks. That\u2019s because dry winter air further helps the influenza virus to remain infectious longer. Dry air, which is common in the winter, causes the water found in respiratory droplets to evaporate more quickly. This results in smaller particles, which are capable of lasting longer and traveling farther after you cough or sneeze.\u201d<\/p>\n Winter vomiting bug rising in the U.S.<\/p>\n For now, surging cases of Norovirus, or winter vomiting bug<\/a> seem to be concentrated in the U.S., with a recent waste water analysis<\/a> by Stanford University suggesting a nationwide rise in cases.<\/p>\n