By mid-February, one category of virus had killed more than 16,000 people in the U.S., including 105 children, and infected more than 29 million Americans, according to the Centers for Disease Control.
The virus is commonly known as the old-fashioned, horrible flu.
As health threats go, the flu virus is the most dangerous virus at large in the U.S., and most deadly to those who have underlying conditions such as asthma or weak immune systems. That observation comes directly from the Centers for Disease Control website, not from a news organization or social media site.
By February, the death toll from flu was the highest for the last 15 seasons. Two main types of flu have been circulating since the beginning of the current flu season. In the early flu season, influenza B/Victoria reigned and late in the flu season there was a surge of influenza A(H1N1)pdm09.
Flu vaccines do help.
For influenza B/Victoria the flu vaccine's effectiveness is 56 percent for children ages 6 months through 17 years and 50 percent for the overall population.
For A(H1N1)pdm09, the vaccine is 51 percent effective for children and 37 percent for the overall population.
The hallmarks of the influenza virus are fever and lung involvement.
