The current influenza season is on the rampage, widely circulating across almost the entire country, the Centers for Disease Control said. The flu epidemic is now widespread in 49 US states, killing at least 22 children this year.

Although, the widespread influenza activity is up from 44 states reported last week, but the surge was not as dramatic as it was a week earlier. CDC said that Florida is the only state reporting just regional outbreaks.

"Flu activity has continued to increase, but not quite as dramatically as the increases we've seen over the previous 2 weeks," said Nancy Cox, MD, chief of the CDC's influenza division. "From a 10-year perspective, we are within the normal parameters of what we'd expect for an influenza season," she continued.

Last week, the World Health Organization expressed their concern about the ongoing bad flu season. WHO said the current influenza season is getting so worse that it can overpower the existing method of treating the infections.

Issuing the warning together with the CDC, U.S. officials said that in the surging influenza season virus can mutate, thus turning the current vaccines into inefficient methods to stop the infections.

Influenza (commonly known as "the flu") is an acute respiratory illness caused by one of the family of influenza viruses. In infants, persons over the age of 65 years, and those with chronic medical conditions, flu can lead to pneumonia, hospitalization, and even death. Each winter, influenza engulfs 36,000 lives in America, most of them elderly and children, and more than 200,000 people are hospitalized with flu-related complications.

According to CDC, although H1N1 subtypes of influenza were more common at the beginning of the season in the United States, the predominant subtype is still A/H3N2.

Why the flu season is getting worse is partly because this year's vaccine is a good match for only about 40% of the viruses, while the flu shots can fend off 70% to 90% of flu bugs in good years, CDC said.

What worried the health agencies most is that this year’s flu vaccine is no longer able to cover all the strains of the viruses that have been circulating throughout the country. Some of the circulating viruses differing from those in the vaccine, the CDC said.

"This year we have two new virus that have cropped up unexpectedly and our flu vaccine coverage hits about 40% of what we are seeing now," said Dr. Michael Richardson of Charlotte Medical Clinic.

Flu vaccines contain the three most common circulating strains, usually two from the Type A family of influenza, and one from Type B. But, the FDA decided this week that three new strains of the virus will be used for next year's vaccine because all three previously used strains have mutated.

Federal health officials on Thursday announced the selection of A-Brisbane/59, A-Brisbane/10, from the Type A family of influenza, and B-Florida, from Type B, for the next season's flu vaccine.