Four new states reported widespread flu activity during the week of Dec. 25, bringing the total number of states with wide geographic spread of the virus to 12, according to the CDC's most recent FluView update.
The 12 states hardest hit so far this season are: California, Connecticut, Idaho, Massachusetts, New Hampshire, New York, North Carolina, Oklahoma, Oregon, Pennsylvania, Virginia and Washington.
Here are five more things to know about the flu season so far.
1. As of Dec. 31, 1,376 lab-confirmed, flu-associated hospitalizations had been reported to the CDC. Most of those (87.7 percent) had influenza A virus. Among those, 98.1 percent were H3N2 strain.
2. The proportion of outpatient visits for flu-like illness was 3.4 percent as of Dec. 31, above the national baseline of 2.2 percent.
3. No pediatric deaths from flu have been reported this season, and the proportion of deaths attributed to pneumonia and influenza was below the epidemic threshold.
4. Most of the flu viruses that have cropped up so far appear to be covered by this season's influenza vaccine. The CDC has antigenically characterized 173 influenza viruses so far, and all but three of the analyzed samples were covered by the 2016-17 Northern Hemisphere vaccine.
5. The majority of the circulating viruses are susceptible to antiviral medications. "Antiviral treatment as early as possible is recommended for patients with confirmed or suspected influenza who have severe, complicated or progressive illness; who require hospitalization; or who are at high risk for serious influenza-related complications," according to the CDC.