There were a record number of flu hospitalizations in Colorado last year. More than 4,600 people were hospitalized due to the flu during the last flu season.

Several factors contributed to a spike in hospitalizations, one of which is the strain, said Dr. Rachel Herlihy, epidemiologist for the Colorado Department of Public Health.

"And last year the predominant strain was a virus called H3N2,” said Herlihy. “And that strain of influenza is really known to cause higher rates of hospitalization and more severe illness, particularly in older adults.”

The strain can change from year to year, said Herlihy, and it can also adapt quickly to vaccinations. However, she points out that getting the flu shot still helps prevent the flu and makes it less severe for healthy adults.