The flu season hit a fever pitch by December, and health care workers aren't yet satisfied the worst is over.
"We certainly had a more active season than we had last year, but last year was more on the mild side nationwide," said Jan Carrasco, immunization coordinator for Grand County Public Health.
Colorado is not in the situation of some states, she said, where medical systems are inundated with flu patients, but Colorado did experience increased flu activity during December - about a month earlier than a typical year.
Initially, Colorado was leading the country in Influenza B, Carrasco said, a form of the flu more prevalent in children, and now the state is seeing an uptick in Influenza A and the H3N2 strain.
"And we don't know if it's hit the peak yet," Carrasco said.
Almost always, strains in vaccines change from year to year. This year's vaccination, containing the old pandemic strain H1N1, a changed B strain and a new H3N2 strain, has been deemed about 62 percent effective, according to the Centers for Disease Control and Prevention.
Most medical clinics in Grand County report moderately high numbers of cases of flu, and the majority of patients with a positive diagnosis had not received a flu shot, according to health workers.
At Ten Mile Clinic in Granby, Dr. Jeff Lipke said as high as 80 percent of patients he's seen with the flu had not gotten a shot this year.
Peak Pediatrics in Winter Park reported about 10 cases of patients with flu so far, three of whom had been vaccinated and still came down with flu.
At the Middle Park Medical Center, Infection Control Nurse Deanna McLain said a total of only 20 patients at both Kremmling and Granby locales have been diagnosed with influenza, a number she deems low. She credits citizens' good hand-washing, flu shots and staying home when sick as perhaps keeping a flu outbreak at bay this year.
Grand County Public Health alone has administered as many as 1,000 doses of the vaccine already, according to Carrasco.
But Byers Peak Family Practice in Winter Park and Fraser Medical Clinic in Fraser are reporting relatively high incidences of flu this season.
Signs of the flu as opposed to a cold are fatigue, body aches, chills and a fever. A respiratory disease, influenza should not be confused with any stomach bug, McLain said. "There's no influenza strain that causes stomach problems," she said.
Public health care workers are encouraging citizens at risk - those pregnant, babies, children with asthma, the elderly, and people with health problems - to still get their flu shots, saying it's not too late.
Healthy people should also get shots, they say, since once contracted, the flu can spread very easily.
Because of the potential economic factor from influenza, losses in productivity due to workers calling in sick, public health workers will visit places of business to administer flu shots where employers are willing to offer shots as an employee benefit.
It may take up to two weeks for protection from flu to develop after the vaccination is taken. Protection then lasts about a year.