The Regional Medical Center in San Jose, Calif., has set up a flu tent near its emergency room to treat patients, as the highly infectious virus has become more widespread throughout the region.

So far, a total of 15 people have died in California, according to ABC's affiliate KGO. The Centers for Disease Control and Prevention has reported that more than 20 states have high flu activity with the H1N1 virus being the most prevalent nationwide.

In the past four years, the CDC has changed its recommendations and now urges all Americans six months and older get a flu shot. Children under the age of 9, who are getting immunized for the first time, should get two doses, one month apart.