The Center For Disease Control:
The most recent FluView report shows increasing flu activity in the United States. Further increases in activity are expected in the coming weeks. Flu activity most often peaks in February and can last into May. It is not too late to get your flu vaccine this season. Flu vaccines this season have been updated to better match circulating viruses and most circulating viruses so far are still like the recommended vaccine viruses for this season.
CDC recommends a yearly flu vaccine for everyone 6 months and older. Vaccination can reduce flu illnesses, doctors' visits, and missed work and school due to flu, as well as prevent flu-related hospitalizations. More than 145.6 million doses of flu vaccine have been distributed in the United States. It takes about two weeks after vaccination for protection to set in, making now the perfect time to get vaccinated. Find a Vaccine.
For more information on flu symptoms, treatment and prevention, read the CDC's "Flu and You" publication.