Twenty-one thousand college students are sick, public schools across Texas and Oklahoma are closing, and more than half the 50 states are reporting widespread flu activity.

Just one week before the first batch of vaccine becomes available, the H1N1 flu is barreling across the country like a runaway freight train.

According to the most recent information available from U.S. Centers for Disease Control and Prevention, which is from last week, 26 states have reported widespread influenza activity, 11 states have reported regional influenza activity, and 12 states, the District of Columbia, and Puerto Rico reported local influenza activity. One state reported just "sporadic" activity.

“H1N1 has become widespread in more than half (of the U.S.), so the virus is definitely picking up,” CDC spokesman Tom Skinner told FOXNews.com. “We had a lull right before school started up, but once it was back in session, we saw it pick up again.”

Although the rate of activity is high, it has not hit epidemic status, Skinner said, adding that some areas are seeing more activity than others, but flu infections are no higher now than they are at the peak of the regular flu season.

“It’s not unusual to see some areas hit harder than others,” he said. “That’s why we’re trying to get the vaccine out as soon as possible.”

The Southern U.S. has been hardest hit with every southern state between Virginia and California reporting widespread flu activity.

In Texas, for example, all schools in the Huntsville Independent School District are closed until Thursday due to students and staff being sick.

A statement on the school’s Web site says classes and extracurricular activities Tuesday and Wednesday at the eight campuses, with nearly 6,300 students, are canceled “due to a high rate of absences.”

"Ninety-nine percent of what’s circulating right now is H1N1 – that’s not to say it won’t change – we’re watching," said Dr. Amy Ray, an infectious disease and public health specialist with University Hospitals Case Medical Center in Cleveland, Ohio. "It’s unusual to see influenza circulate during the summer months, transmission is increasing."

On Monday, 14 percent, or 885 students, of the student population were absent, citing illness as the reason, Huntsville ISD Assistant Superintendent John DeBrock told MyFoxHouston.com.

Skinner said the CDC has provided school districts with guidance as to how to deal with H1N1 but has left it up to individual districts as to whether and when to close.

“School officials are in the best position to make (the call to close schools),” Skinner said. “Certainly, as a last resort, if it thinks it needs to close because the absentee rate is impacting its ability to function than it should do so.”

Many of the ill in the Huntsville District include staff and teachers. The district’s custodians will be cleaning the schools from top to bottom while students and teachers are out of the building, DeBrock said.

“They’re going to be primarily concentrating on high-contact areas, tabletops, desktops, water fountains,” DeBrock said.

Concerns about H1N1 and other illnesses have led to numerous absences at schools throughout Texas.

In Austin, Texas, Dell Children’s Hospital has set up tents outside of its emergency room to deal with the influx of flu cases that have appeared this past week. Dr. Pat Crocker, chief of Emergency Services, told the Washington Post the number of patients the ER is seeing per day has shot up from 140 to 380.

Additionally, hospitals in Charlotte, N.C. have joined a nationwide trend of banning children from visits to patients as a precaution against spreading the flu virus.

The Charlotte hospitals join hospitals in New York, Arizona, and Iowa who have taken similar precautions. Some hospitals only ban young visitors from the maternity ward. Pregnant women are at especially high risk for the virus.

The CDC has not offered an opinion as to whether children should be banned from hospitals, Skinner said.

“That’s up to each hospital to do what is best,” he said. “We’ve offered guidance on taking care of people who are sick with the flu that may help to curb the spread of the disease. But if they feel something like keeping children away from sick patients may also help with curbing the spread, than they certainly have the prerogative to do that.”

In the meantime, how can people protect themselves?

"Stay home if you become sick, seek medical care, practice good hygiene such as covering your mouth when you cough or sneeze, wash your hands frequently," Ray said. "As we’re awaiting vaccine, and even after its delivered -- patients who are at high-risk seek medical care early."

FOXNews.com health editor Jessica Doyle contributed to this report.