April 30 (HealthDay News) -- The World Health Organization on Wednesday raised the swine flu epidemic level from 4 to 5, signifying that a pandemic is imminent, and urged countries to implement their pandemic plans.
The warning underscored the concern of world health officials that the outbreak could trigger large numbers of deaths worldwide, even though there have only been eight confirmed deaths in Mexico -- believed to be the source of the outbreak -- and one in the United States, the Associated Press reported.
"It really is all of humanity that is under threat during a pandemic," WHO Director General Margaret Chan said in Geneva, Switzerland. "We do not have all the answers right now, but we will get them."
In Washington, President Barack Obama promised "great vigilance" in confronting the outbreak that has sickened nearly 100 people in 11 states and forced many schools to close.
All of the cases diagnosed in the United States have continued to be mild, federal health officials said Wednesday.
A 23-month-old Mexican boy who had traveled to Houston for medical treatment died Monday night, becoming the first fatality in the United States. And 39 Marines were confined to their base in California Wednesday after one came down with the disease.
Switzerland on Thursday became the latest country to report a swine flu infection -- a 19-year-old student. The virus has also spread to Canada, New Zealand, Britain, Germany, Spain, Israel and Austria, the AP reported.
An estimated 170 deaths in Mexico are believed to have been caused by the never-before-seen virus, according to published reports. The new flu strain is a combination of pig, bird and human viruses, prompting worries from health officials that humans may have no natural immunity to the pathogen.
The WHO's Phase 5 alert prompted Mexico to further restrict activity in that country in an effort to cut down on human-to-human infections, including a suspension of nonessential federal government activities, Mexican Health Secretary Jose Cordova said late Wednesday. Schools in Mexico had already been canceled until May 6, the AP said.
Mexico's efforts may be paying off -- the outbreak seemed to be stabilizing; confirmed swine flu cases doubled Wednesday to 99, but new deaths finally seemed to be stabilizing, the news service said.
Meanwhile, President Obama said Wednesday that U.S. public health officials were recommending that schools with confirmed or suspected cases of swine flu "should strongly consider temporarily closing so that we can be as safe as possible."
Texas has postponed all public high school sports and academic competitions at least until May 11 due to the outbreak.
At a press briefing Wednesday morning, Dr. Richard Besser, acting director of the U.S. Centers for Disease Control and Prevention, said there were 91 confirmed cases of infection with the swine flu virus in 10 states, with the one death. Sixty-four percent of the cases involve people under age 18, but patients range in age from 8 to 81, he said.
Kathleen Sebelius, the new secretary of U.S. Health and Human Services (HHS), said at the briefing that, "while we still don't know what this virus will do, we expect to see more cases, more hospitalizations and, unfortunately, we are likely to see additional deaths from the outbreak."
"Currently, the FDA [U.S. Food and Drug Administration] and the CDC are developing virus reference strains -- the information that is necessary to develop a vaccine," Sebelius said. "Today, there are a series of steps that HHS is taking in vaccine development. The process is more speedy than it has ever been before."
The earliest a vaccine could be ready is this fall, said Dr. Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases.
During a press briefing Tuesday, Besser had said that the cases of infection found in the United States so far continued to be mild, but more severe cases were expected, and "as we move forward, I fully expect we will see deaths."
Besser said the incubation period for the U.S. cases is two to seven days, which, he said, "is typical for what you see with an influenza virus."
Many of the swine flu cases in the United States come from a New York City high school, Besser said. Some students at St. Francis Preparatory School in Queens had traveled to Cancun in Mexico for a spring break trip, according to news reports.
As with the previously tested strains of the swine flu virus, new testing found that the pathogen remains susceptible to the two common antiviral drugs Tamiflu and Relenza, according to an April 28 dispatch from the CDC's Morbidity and Mortality Weekly Report.
SOURCES: April 29, 2009, teleconference with Richard Besser, M.D., acting director of the U.S. Centers for Disease Control and Prevention; Kathleen Sebelius, secretary, U.S. Health and Human Services; Associated Press