Gearing up: 'Pandemic' doesn't necessarily mean 'severe' illness, just new, widespread

Still, the future virulence of the outbreak is uncertain, and government agencies and vaccine-makers are gearing up to deal with a potentially unpredictable flu season.

"Pandemic" means the virus is novel - humanity carries no built-in immunity to it - and spreading worldwide. Previous pandemics occurred in 1997 (avian A/H5N1 flu), 1976, 1968, 1957 and 1918, the latter being the Spanish flu, which killed an estimated 40 million to 50 million people worldwide, according to the WHO.

Due to the relative mildness of H1N1 to date, she says she hasn't developed a pandemic flu plan.

No severe threat - yet

H1N1 doesn't pose a major public health threat at the moment, sources say.

"It seems that because most of the cases have responded to Tamiflu (oseltamivir phosphate, Roche), H1N1 doesn't have potential to stop meetings like SARS did in Asia," says Robert Weiss, M.D., president of the American Society for Dermatologic Surgery.

"Right now, H1N1 is not behaving that badly for an influenza virus," says Raymond J. Dattwyler, M.D., professor of medicine and microbiology/immunology and chief of the Division of Allergy/Immunology and Rheumatology at New York Medical College, Valhalla, N.Y.

However, "The fear is that as it infects people, it's going to mutate or exchange viral DNA with other influenza viruses and become more virulent," Dr. Dattwyler says.

Should H1N1 mutate into a nontreatable virus, Dr. Weiss says, "It would be really bad for an economy that's starting to recover." And patients concerned about skin cancer or other skin issues will "certainly think twice about coming into an office where they could possibly be exposed."

Unlike seasonal flu, H1N1 attacks primarily children and young adults up to age 24, and it's less severe, says Joseph Quimby, senior press officer with the Centers for Disease Control and Prevention (CDC).

Seasonal flu can cause more than 200,000 hospitalizations and 36,000 U.S. deaths yearly, he says. In contrast, as of July 24, the CDC had tallied. 43,771 confirmed and probable U.S. H1N1 cases, and, as of July 31, 5,514 hospitalizations and 353 deaths.

Because mild cases go unreported, CDC case totals represent "the tip of the iceberg," Mr. Quimby says. (In fact, the CDC has stopped reporting case totals.)

CDC experts predict 1 million to 1.5 million U.S. H1N1 cases this flu season, Mr. Quimby adds.

"We're prepared for both an active influenza season this fall and a ramp-up of H1N1," he says.

Vaccine in development

To combat H1N1, U.S. Department of Health and Human Services Secretary Katherine Sebelius plans a voluntary national inoculation campaign for the 2009/2010 season - provided a safe, efficient vaccine is available, Mr. Quimby says.

Without a vaccine, the CDC estimates that up to 40 percent of the U.S. population could contract H1N1 over two years.

At press time, a vaccine was still under development.

"It's anticipated that we will see clinical trials throughout August," Mr. Quimby said in late July. "It may be mid-September before all those data are available."

By the time the Food and Drug Administration approves a vaccine, "We will have seen the severity or lack thereof of an active influenza season in the Southern Hemisphere," were both H1N1 and seasonal flu are present, he says.

This information will help determine how much H1N1 vaccine the country needs, and whether H1N1 has changed, he says.

U.S. companies producing H1N1 vaccine include Sanofi Pasteur, Novartis, Medimmune, CSL and GlaxoSmithKline. Planners should assume vaccine administration will begin this fall, the CDC Web site states.

Disclosures: Drs. Dattwyler, Weiss and Lowenstein report no relevant financial interests.

For more information: http://www.cdc.gov/