The country is gripped by a winter flu season that has struck every state in the U.S. and even shut down some schools.
During the third week of January, the number of states with flu outbreaks more than doubled, the Centers for Disease Control and Prevention (CDC) reported.
The states hardest hit with influenza outbreaks to date are Arizona, Georgia, Massachusetts, Nebraska, Nevada, North Carolina, Virginia, and Washington. New York City also is on the list of hardest-hit places.
The infectious viruses spread so quickly in Halsey, Oregon, that an entire school district shut down for two days. The students and staff of the Central Linn district were given a four-day weekend to recuperate, or to avoid catching the sickness.
The Oregon Department of Education said it was the first time that a district of this size - 700 students - has shut down because of illness. School officials said that on Wednesday, 160 students and 18 staff members called in sick.
In Spearfish, S.D., the flu also led to cancellaton of classes through the weekend. The superintendent for the Lead-Deadwood School District called off school Wednesday because about a third of students and staff had called in sick.
In Illinois, the Astoria School District superintendent canceled classes Thursday because more than a quarter of area high school students were ill.
The CDC has said that cases of influenza type A have been most prevalent across the country. Type A can be treated with antiviral drugs such as amantadine and rimantadine, which can cut short the duration and harshness of influenza.
According to the CDC, an average of 20,000 people die every year from complications of flu and pneumonia. During the third week of January, the percentage of deaths blamed on the illnesses reported by 122 U.S. cities was 7 percent, below the epidemic threshold of 7.4 percent.
Researchers say that this winter's flu vaccine effectively protects against all of the flu strains that have been detected. While the CDC suggests that people get the vaccine before the flu season is under way in mid-November, this year's outbreaks have prompted health officials to recommend late-season vaccinations.