Thousands of school children in the U.S. have been sent home, as fear of swine flu spread across the country and new cases were confirmed.
Most of the school closings are in Texas, where more than 50,000 students are at home.
On Wednesday, U.S. health officials announced that a 23-month-old Mexican boy who had traveled to Texas died from the disease, becoming the first U.S. fatality.
But Dr. Jeffrey Starke said the boy's death should not spark alarm in the U.S. "This child did not acquire this virus in Houston, Texas," he stated.
At the White House Wednesday, President Obama said his administration is doing everything possible to deal with the outbreak. He urged local jurisdictions to be vigilant.
"It's also the recommendation of our public health officials that schools with confirmed or suspected cases of H1N1 should strongly consider temporarily closing so that we can be as safe as possible," Mr. Obama said.
Late Tuesday, Kathleen Sebelius was sworn in as secretary of health and human services after being confirmed by the US Senate.
Some Senators are suggesting that the Obama administration should consider closing the U.S.-Mexico border. But at a Senate hearing Wednesday, Homeland Security Chief Janet Napolitano said there is no proof that would help.
"If the CDC [Centers for Disease Control] told us that closing the border would have a significant impact on the prevention of disease within our country, I think that would be a highly relevant factor," she said. "But the analysis has been that closing ports, closing the border, would not have that kind of preventive impact."
Admiral Anne Schuchat of the U.S. Centers for Disease Control and Prevention, said her agency is working to develop a "virus strain" for use in a vaccine against the swine flu. "If everything went great, production could lead to availability as early as September," he said.
She said authorities would also have to determine which people could receive such a vaccine without suffering complications.
Meantime, officials across the country had the same advice about prevention.
"Keep your hands washed, cover your mouth when you cough, stay home from work if you are sick, keep your children home from school if they are sick," Mr. Obama advised.
