Like an early harbinger of spring, the influenza virus is sprouting across Southern Oregon.

Like an early harbinger of spring, the influenza virus is sprouting across Southern Oregon.

For the past five years, the flu season has peaked in Oregon around the end of February and early March, and this year seems to be no exception. Public health officials have seen a spike in the number of flu cases over the past three weeks, and there's likely more to come, says Dr. Ann Thomas, who monitors influenza activity across the state.

"We're expecting it to last for a few weeks," Thomas said.

Influenza is characterized by sudden onset, body aches and muscle pain, fever, headache, extreme fatigue, loss of appetite, a dry cough and pain when the eyes move. The common cold is centered around the nose, with symptoms such as sneezing, nasal congestion and runny nose.

Fever is common with the flu, and relatively rare with a cold.

Thomas encouraged anyone who has not yet been immunized against this year's flu to get a shot. Most people recover from the flu, but it's a debilitating illness that can last for weeks. Researchers estimate about 36,000 Americans die from the flu each year, mostly those who are weak from advanced age or a major illness.

The vaccine "only takes two weeks to start working," she said. "It's not too late (to be immunized), and the vaccine is the most effective way to prevent the flu."

Thomas said the incidence of influenza-like illness, or ILI, spiked dramatically in recent weeks at "sentinel" clinics across Oregon that track the percentage of patients who come in with flu-like symptoms.

Just 2 percent of patients had flu-like symptoms in Southern Oregon during the third week in January, but for the first three weeks of February it has been 10 percent, 12 percent and 11 percent, respectively.

Student absence at Medford schools was about average Monday, except for Ruch Elementary School, where 25 of the school's 180 students (nearly 14 percent) were home sick.

"Ruch is taking it hard," said Jodi Bostwick, a nurse for the Medford School District. "It's not just the kids. The families are sick, the secretary said."

Thomas noted this year's flu vaccine is good match for the strains of the influenza virus that are most widespread this year. New vaccine is produced every year, and researchers have to guess which strains of flu are likely to be most prevalent. Flu vaccine also provides some measure of protection against other strains that are not in the vaccine, which can reduce the severity of illness.

There's plenty of vaccine available, and a recent change in Oregon law allows pharmacists to immunize adults. Many stores with pharmacies now offer immunizations for flu, pneumonia, shingles, and tetanus.

"It's a good year to get a flu shot," Thomas said.

Reach reporter Bill Kettler at 776-4492 or e-mail:bkettler@mailtribune.com