Other hospitals in the USA have limited the age of patients under five years old as younger patients may not show signs of the flu but could be highly infectious.
The number of people testing positive for influenza also is significantly higher than in past years across the state and nation. Vaccines can reduce overall risks, according to the U.S. Center for Disease Control.
"In general, we get in our season what the Southern Hemisphere got in the season immediately preceding us", Dr. Anthony Fauci, director of the United States' National Institute of Allergy and Infectious Diseases, said during Australia's flu season previous year.
Vocational nurse Ilda Villahermosa, right, rubs Melanie Valdez's arm where she had recieved a flu vaccine shot at the Kaiser Permanente Redwood City hospital on December 28.
Vaccine manufacturers, the World Health Organization and others are studying the situation to determine if that was the case, she said.
"We know that the years when there are H3N2 strains that predominate, those are more severe years - meaning there are typically more infections, more severe infections, more hospitalizations and more deaths". California only records flu-related deaths of people under age 65, largely because fatalities among older people are so common that reporting them all would overwhelm surveillance systems. "The vaccine helps your body develop protection in two weeks and can lessen severity if one gets the flu".
To make matters worse, some pharmacies are dealing with temporary shortages of flu medications due to demand.
Antiviral drugs are different from antibiotics. For information on how to prevent or treat the flu, visit the CDC's website.
H3N2 has been responsible for some of the worst flu seasons in the United States in recent years, including the 2006-2007, 2012-2013, and 2014-2015 bouts. Oseltamivir is available in different formulations in generic and under the trade name 'Tamiflu, ' and zanamivir is available under the tradename 'Relenza, ' " she wrote.
He added that both children and pregnant women are among those at higher risk due to the flu, as are people over the age of 63. "It's not too late", said Dr. Cora Hoover, director of communicable disease control and prevention with the San Francisco Department of Public Health.
Flu activity is now widespread across Tennessee and the USA, and everyone over the age of six months old that has not yet had a flu vaccination this flu season is urged to get one now, officials said.
An estimated 9.2 million Americans have gotten sick with the flu each year since 2010.
He said people should avoid visiting those places if sick. Wash your hands frequently and avoid touching your mouth, nose and eyes.
In general, get plenty of sleep, be physically active, manage your stress, drink plenty of fluids, and eat nutritious foods to stay healthy.