The 2019-20 flu season is underway and it’s already proving unpredictable in Colorado as the type of influenza making the rounds is one that normally doesn’t appear this soon.
Influenza B, a strain that typically doesn’t show up until the end of the season, has appeared in most flu cases this year. However, the number of Coloradans sick with the flu is normal, health officials said.
So far, more than 200 individuals have been hospitalized for flu this season, according to data from the state Department of Public Health and Environment.
“It’s definitely not considered a severe season for us,” said Dr. Suchrita Rao, an infectious disease specialist at Children’s Hospital Colorado, noting that it’s still early in the flu season.
It’s unclear why there’s an early flurry of influenza B activity, but it could be because there were two waves of influenza A activity last flu season, she said.
Last season, flu hospitalizations were mostly caused by the H1N1 virus, which is less aggressive than the H3N2 virus, which in 2017-18 contributed to one of Colorado’s worst flu seasons.
This year, the second-most common strain making the rounds is H1N1, which is notable for causing the flu pandemic of 2009, according to the Centers for Disease Control and Prevention.
The main difference between influenza B and influenza A — which includes both H1N1 and H3N3 viruses — is that the former is known to show up more in children, said Dr. Rachel Herlihy, state communicable disease epidemiologist.
“The predominance of influenza B right now is unusual,” she said. “It’s possible, just as we did last year, to see two waves of influenza.”
Both influenza A and influenza B strains cause the same illness. Flu symptoms include fever, cough, sore throat, chills, headaches, fatigue, and a runny or stuffy nose, according to the CDC.
It’s too early to know how well the flu vaccine matches the strains circulating this season, but Herlihy is encouraging everyone six months and older to get the shot, especially high-risk groups, such as older adults, pregnant women and individuals with chronic illnesses.