Flu season has finally begun in the U.S., according to one measure used by the CDC.

For the first time this season, the proportion of respiratory specimens that tested positive for influenza nationally reached 10.5% for the week ending February 4. Passing the 10% mark is one indication that flu season has begun.

Other markers of influenza activity are also off to a slow start this year, the CDC reports, but the agency says it expects activity to pick up. To date, the circulating viruses have been well matched to this year’s influenza vaccine.

Source:CDC