The World Health Organization may have just declared a pandemic of the H1N1 flu virus, but the United States has been acting as if a pandemic was under way for weeks, health officials said on Thursday.

The new swine flu virus was first identified in two U.S. children in April and by the time the news was out, it had already begun spreading. CDC experts estimate that hundreds of thousands of people are likely infected in every state.

Although most had mild symptoms, there have been at least 27 deaths and 1,000 people have been sick enough to be hospitalized.

Dr. Thomas Frieden, who has been in his job as CDC director for just four days, told a news conference the WHO declaration did not come as a surprise. “There are no practical implications for most state and local governments,” he added.

“Here in the United States, the basic declaration isn’t going to change our day-to-day activities,” added the CDC’s Dr. Anne Schuchat.

WHO raised its pandemic flu alert to phase 6 on a six-point scale, indicating the first influenza pandemic since 1968 is under way.

Based on the U.S. experience, what can the rest of the world expect?

The new H1N1 disproportionately makes younger people sick. Schuchat said 57 percent of U.S. cases were among people aged 5 to 24, and 41 percent of those hospitalized were in this younger age group.

“The highest rates of hospitalization are actually in children under 5,” Schuchat said. Pregnant women, people with asthma or other chronic respiratory disease and diabetics needed to take special care and call a doctor if they had symptoms.

H1N1 is active in all 50 states and there are so many cases now that in some areas, patients with specific flu-like symptoms - a fever above 104 degrees F, cough or other respiratory symptoms - are presumed to have the new virus.

YEARS OF PLANNING

The United States, like other countries, has been planning for an influenza pandemic for years.

Stockpiles were made of antiviral drugs - Tamiflu (generic name oseltamivir) and Relenza (generic name zanamivir) - and state, local and federal officials held distribution exercises.

Work on an H1N1 vaccine is under way. The Health and Human Services Department has ordered $650 million worth of vaccine ingredients from its five corporate suppliers and $287 million worth of boosters called adjuvants that can be used to make vaccines work better.

Schuchat said there had been “some challenges” but did not elaborate. CDC and the Association of State and Territorial Health Officers plan a series of “lessons learned” meetings, she said. “I think this will be really vital information to help us react better in the fall,” Schuchat said.

There may be good information for health officials in the Southern Hemisphere, where flu season is just getting under way, she said. Other pandemics have started out as a moderate flu season in the spring, only to surge back and be more deadly in the autumn.

One big worry is that seasonal H1N1 and H3N2 viruses are still circulating. The seasonal H1N1 has mutated into a form that resists Tamiflu, although it is still susceptible to Relenza.

Schuchat and other experts fear if someone got infected with two strains at the same time, the viruses could recombine in the patient’s body and acquire new strengths and new drug resistance. “We really don’t want this novel H1N1 to become resistant to Tamiflu as well,” Schuchat said.

By Maggie Fox
WASHINGTON (Reuters)