Late and mild flu season wrapping up

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ATLANTA, June 1 (UPI) -- The U.S. flu season, which started late and was mild compared with other seasons, is wrapping up, federal health officials said.

A report by the Centers for Disease Control and Prevention said this year's flu season set a new record for the lowest and shortest peak for influenza-like illness since this type of surveillance began in 1997-1998.

"This is the first time since CDC started this kind of influenza-like-surveillance that the percentage of patient visits for influenza-like-surveillance was elevated for only one week of the season," Dr. Joseph Bresee, chief of the epidemiology and prevention branch in CDC's influenza division, said in a statement. "In terms of influenza-like-surveillance, this not only the shortest time we were elevated but it's also the lowest 'peak' ever recorded."

In typical years, influenza-like illness remains elevated for about eight to 20 weeks, with an average of 13 weeks, Bresee said.

"The reason for the mildness and lateness of the season isn't certain, but it's likely that there were a number of contributing factors, including a mild winter, the fact that most of the influenza viruses circulating this season were similar to those that have circulated for the past two seasons, and the fact that most circulating viruses were similar to the viruses that the 2011-2012 vaccine was designed to protect against," Bresee said.

"The low levels of influenza virus 'drift' -- change -- for two consecutive years and steadily increasing influenza vaccination coverage in the country likely contributed to broad levels of immunity in the population."