It's the latest start for a flu season in 29 years, and thus far, severe cases have been few. But that doesn't necessarily mean Americans have dodged any seasonal illness bullets. Influenza is just beginning to gain a foothold around the country.
"The flu season has officially begun," Dr. Joseph Bresee told reporters Friday morning during a briefing at the agency's headquarters in Atlanta.
Infections have reached all 50 states, said Bresee, who is chief of the epidemiology prevention branch at the U.S. Centers for Disease Control's influenza division. Most of the viruses that have been detected this year are "well matched to the strains in the 2011-2012 influenza vaccine," Bresee reported, and all of the strains are susceptible to antiviral medications. Influenza A H3N2 and H1N1 viruses and influenza B viruses have been detected.
Bresee said that a variety of factors may have contributed to the mild, late flu season. First, this year's viruses are similar to last year's, which means many people already have some immunity to the strains. Vaccine coverage is improving. The warm weather, too, could help keep flu infections at bay. Flu viruses remain viable longer in colder weather, he said, and people are less likely to "cluster inside," which can promote disease transmission.
Bresee said that epidemiologists at the CDC expected seasonal flu activity to increase in the coming weeks, and that flu seasons have peaked as late as April in years past.
"If you haven't gotten the flu vaccine yet or your loved ones haven't gotten theirs yet, get your vaccine now," he said. "It's not too late."
Read a summary of the CDC's weekly FluView here.