GENEVA, Switzerland (CNN) -- The World Health Organization raised its pandemic alert to 5, its second-highest level Wednesday, indicating the outbreak of swine flu that originated in Mexico is nearing widespread human infection.
Dr. Margaret Chan, the U.N. agency's director-general, said the decision mean to raise the alert to 5 on its 6-point scale indicated that all countries should "immediately" activate pandemic preparedness plans.
"This change to a higher phase of alert is a signal to governments, to ministries of health and other ministries, to the pharm industry and the business community that certain actions now should be taken with increased urgency and at an accelerated pace," Chan said.
The annoucement came as the number of people infected with swine flu increased rapidly across the world, and health officials scrambled to get more information about the virus -- which has no vaccine.
Germany and Austria became the latest European countries to report swine flu on Wednesday, while the number of cases increased in the United Kingdom and Spain.
The WHO and national governments have confirmed 148 cases of swine flu in 11 countries. Most of those are in the United States, where the Centers for Disease Control and Prevention has confirmed 91 cases.
The figures include seven deaths in Mexico and one in the United States. More than 2,700 other patients worldwide are believed to be suffering from the virus, known scientifically as H1N1.
The WHO's "Phases of Pandemic Alert," which has been in existence for five years, characterizes phase 5 as a human-to-human spread of the virus into at least two countries in one WHO region, which signals that a pandemic is imminent.
The highest level, phase 6, is defined by community-level outbreaks in at least one other country in a different WHO region, according to the agency.
"The question now is how severe will the pandemic be, especially now at the start," Chan said. "It is important for us to take this very seriously and take vigilance as the virus evolves."
The Pentagon is planning for a task force that would help with transportation, logistics and distributing medical supplies in the event of a pandemic, a spokesman said.
The U.S. government is distributing 25 percent of its stockpile of antiviral medications Tamiflu and Relenza to all states, Homeland Security Secretary Janet Napolitano said Wednesday. Health officials stress that the medications are effective only if taken in the early stages of the infection.
Researchers also are conducting a complete genetic sequencing of the H1N1 virus as the federal government considers more effective methods of combating the swine flu outbreak, a health official told a Senate committee Wednesday.
The 91 confirmed cases in the United States includes the country's first swine flu fatality: a 22-month-old child from Mexico who died of the illness Monday at a Houston, Texas, hospital.
A U.S. Marine in California is the military's first suspected case of swine flu, and three military family members in San Diego have confirmed cases, the Defense Department said.
As a precaution, the military is banning travel to Mexico for nonessential personnel.
The first cases of the virus were detected in Mexico, where health officials suspect swine flu in more than 150 other deaths and roughly 2,500 illnesses. Only 26 cases have so far been confirmed, including the seven fatal cases.
The deadly outbreak has prompted authorities to order about 35,000 public venues in Mexico City to shut down or serve only takeout meals as health officials tried to contain spreading of the virus.
Mexican officials also said they believe they may have found "patient zero" -- the first case of the global outbreak -- in the small mountain village of La Gloria.
Edgar Hernandez, 5, survived the earliest documented case of swine flu. He lives near a pig farm, though experts have not established a connection between that and his illness.
Edgar has managed to bounce back from his symptoms and playfully credits ice cream for helping him feel better.
President Obama called on schools with confirmed or possible swine flu cases to "consider temporarily closing so that we can be as safe as possible."
At least 74 elementary, junior high and high schools have closed across the country due to confirmed or probable cases of swine flu, the Department of Education said Wednesday.
Another 30 schools have closed as a precautionary measure, Department of Education spokesman Massie Ritsch said.
Researchers do not know how the virus is jumping relatively easily from person to person, or why it's affecting what should be society's healthiest demographic. Many of the victims who have died in Mexico have been young and otherwise healthy.
Governments around the world are scrambling to prevent further outbreak.
Some countries, such as China and Russia, have banned pork imports from the United States and Mexico, though the WHO said the disease is not transmitted through eating or preparing pig meat. Several other countries, such as Japan and Indonesia, are using thermographic devices to test the temperature of passengers arriving from Mexico.
Egypt reportedly is considering culling all pigs although there have been no reported cases of swine flu there.
Swine influenza, or flu, is a contagious respiratory disease that affects pigs.
When the flu spreads person to person, instead of from animals to humans, it can continue to mutate, making it harder to treat or fight, because people have no natural immunity.
Symptoms include fever, runny nose, sore throat, nausea, vomiting and diarrhea.
Common seasonal flu kills 250,000 to 500,000 people every year worldwide, far more than the current outbreak of swine flu. But there is a vaccine for seasonal flu.