WASHINGTON -- The United States has activated an emergency plan to combat swine flu as the Obama administration announced measures Sunday to contain the sometimes deadly virus.

The Centers for Disease Control and Prevention has identified the strain of swine flu and is prepared to distribute a quarter of the U.S. stockpile of 50 million doses of anti-viral medications in places around the country where swine flu has been located or may be expected to spread, Homeland Security Secretary Janet Napolitano said in a briefing at the White House. 

Travel advisories have not been issued by the State Department, Napolitano said, nor is the United States going to screen passengers on flights arriving from Mexico. She said funds have been freed up in case a larger response is needed.

Hand-washing, mask-wearing and other measures will help prevent the spread, Napolitano said explaining how the public can help slow potential contaminations. 

"If you are sick, stay home," Napolitano said. "Take all of those reasonable measures that will help us mitigate and contain" the illness.

People who are ill should not go on airplanes, to school or other places, added Dr. Richard Besser, the acting head of the CDC.

Besser said the United States is working with the World Health Organization, Canada and Mexico as well as other organizations to reduce the spread of the virus, which appears to have originated in Mexico and has resulted in up to 81 deaths there. 

The CDC has issued advice on its Web site on how to avoid the sickness and how to react if people think they are infected. 

Click here for the CDC Web site.

"Every outbreak is unique" and it's very hard to say how long it will be before it's contained. But Besser said since it's near the end of flu season right now, a decline would be likely.

However, he added, "We view this more as a marathon. We do think this will continue to spread but we are taking aggressive actions to minimize the impact on people's health." 

"Even if this outbreak is a small one we can anticipate that we may have a subsequent of follow on outbreak in several months from now," Napolitano said.

In a press conference held Sunday, New York Governor David Paterson said the eight potential cases in Suffolk County have been tested.

"It's a situation we're monitoring but it seems there's no real danger ahead," said Gov. Paterson.

Gov. Paterson said daily updates are being given to 25,000 physicians, hospitals and health care providers.  

In the U.S., 20 cases of swine flu have been confirmed in California, New York, Texas, Ohio and Kansas. Patients have ranged in age from 9 to over 50. Besser said that all the cases have resulted in recovery and one person remains hospitalized.

As the briefing was occurring, Mexico City Mayor Marcelo Ebrard announced that two more people died overnight in the capital of swine flu, and three other deaths are suspected to have been caused by the new strain. 

On Sunday evening, Mexico's health secretary announced the suspected swine flu cases rose to 1,614 with 103 believed dead.

John Brennan, assistant to the president for homeland security, said President Obama has offered his full support to the Mexican government and people. Brennan said early communications and quick response will be the key to combating an outbreak. 

"Early identification is vitally important," Brennan said. "Communications have been robust and medical surveillance efforts are fully activated."

The incubation period for swine flu is 24-48 hours. White House spokesman Robert Gibbs said despite reports Obama did not have a medical exam since it's been nine days since he left Mexico.

Gibbs said earlier Sunday that now is not the time to panic.

"We are increasing the monitoring and preparedness that we would need to have in place in order to deal with any sort of emergency, but it is of concern to the White House," Gibbs said on "Meet the Press."

Israel, New Zealand, Spain, France and Canada have reported suspected isolated cases after citizens from those countries returned home from Mexico.

The Israeli Health Ministry said the biggest concern is a spread of the disease from person to person. 

"The main route of contamination would be from person to person and not from pigs. There is no swine flu in pigs in Israel. There are not many pigs in Israel," said Dr. Hagai Levin.

"You can not get the swine flu from eating pork," Napolitano said during the briefing.

Swine flu is dangerous because it changes its form and takes on characteristics like bird flu, and there is no vaccination, said Dr. Isador Rosenfeld, a FOX News contributor.

However, Baxter International Inc. of Illinois is working with the World Health Organization on a potential vaccine, the company announced Sunday.

"Baxter has the R & D pandemic planning and expertise to develop vaccines for emerging diseases and viruses," Baxter spokesman Christopher Bona told FOX News. "Upon learnign about the swine flu outbreak, Baxter requested a sample of the virus from the WHO to begin lab testing for developing a potential experimental vaccine."

Rosenfeld said swine flu is usually a mild infection. He suggested staying away from crowded places where people are sneezing and coughing and washing hands. But he said he's a bit confounded about why so many people in Mexico have died because swine flu does respond to Tamiflu and other anti-viral medicines.

"This thing is treatable," he said.