Plans under way for coping with potential flu pandemic

Washington -- In the event of the next dreaded pandemic, should it be young adults who first roll up their sleeves to be vaccinated? After all, mortality was highest among 20- to 50-year-olds when the 1918 Spanish influenza hit.

Or should the oldest and youngest continue to have priority, as they do now, during annual flu seasons? Ninety percent of deaths occur annually among those older than 65 and there is also a high rate of hospitalization among young children.

In the event of a pandemic, such decisions will be primary issues. After all, it is not known how long it might take to develop an effective vaccine and, therefore, who should be first in line to receive it. And, although there would be a push to manufacture enough of the appropriate flu vaccine for everyone, initial supplies would likely be less than adequate.

Thus, planning for a deadly pandemic is something of a necessary leap into the unknown. A group of physicians, vaccine manufacturers, bioterrorism experts and epidemiologists recently gathered at the National Academies of Science in Washington, D.C., to advance the process by assessing the nation's prevention and response capabilities.

Taking a look at the toll of sickness and death of the 1918, 1957 and 1968 pandemics, Lone Simonsen, PhD, an epidemiologist at the National Institute of Allergy and Infectious Diseases' Office of Global Affairs, suggested that young adults be considered a high priority group for vaccination.

After all, the 1918 pandemic had a very dramatic impact on young people, she said.

But the picture is complex.

In the 1957 pandemic, infection rates from Asian influenza were highest among school-age children, young adults and pregnant women, although the highest death rate was among the elderly.

The Hong Kong influenza pandemic of 1968, the mildest of the 20th century pandemics, claimed fewer than 34,000 lives, but most were elderly.

Thus, as a national plan to prepare for and respond to a flu pandemic is readied for public view, the need for flexibility is apparent. After all, no one knows what the next pandemic will look like, although public health officials are certain it will arrive.

"Will it be like the 1918 pandemic and be an incredible catastrophic event or will it be like 1968 where probably a large majority of the people didn't even realize there was a pandemic?" asked Ben Schwartz, MD, with the National Vaccine Program Office at the Dept. of Health and Human Services. "Do you plan for the worst case scenario, recognizing that the worst case may not occur and there will be consequences in terms of resources and costs?"

Despite the hurdles, a draft plan, which has been under review for more than two years, is being readied for unveiling. "We hope it will be published in several weeks for public comment," said Dr. Schwartz.

Drifted and shifted viruses

Viral differences could help determine which groups to vaccinate in a pandemic. The viruses that trigger annual flu outbreaks are those that have "drifted" and undergone subtle or small mutations that vary from year to year, said Gregory Poland, MD, chief of the Mayo Clinic's Vaccine Research Group.

While anyone who has not been previously exposed to a drifted virus will be infected by it and have symptoms, those most severely affected are the very young, the very old and those with chronic medical problems. And these are the groups the Centers for Disease Control and Prevention targets for priority vaccination each year.

A pandemic influenza virus is one that has "shifted," meaning that it has had multiple and major mutations so that very few people have ever been exposed to it and widespread outbreaks would likely be much deadlier.

Surveillance is the "keystone" to detecting and identifying a virus in time to develop an effective vaccine to thwart it, said Dr. Poland.

Many people think a new pandemic will emerge in Asia, and attention has been drawn to the avian flu, particularly strain H5N1, which first jumped from chickens to people in 1997.

Research findings published in the July 2 Proceedings of the National Academy of Sciences indicate that sometime around 2001 the virus became more adept at infecting mammals. Researchers inoculated mice with virus samples taken from different years and waited to see which animals became ill.

The mice infected with virus samples from 2001 and 2002 became more ill than did mice that were infected with samples gathered in earlier years. Researchers are concerned that a virus that has acquired the ability to infect mice could also infect humans.

With an eye on the possible need for universal vaccinations in the future, public health officials are debating whether to expand current flu shot recommendations to include everyone before it becomes essential. Such a step would "decrease annual disease, get more people used to getting flu shots and encourage the industry to manufacture more influenza vaccine, which would increase our ability to get vaccine in a pandemic," said Dr. Schwartz.

But until that happens, there are already 185 million people in the United States for whom influenza vaccine is recommended, but last year only 83 million were vaccinated, he noted. "So there is a lot of opportunity to expand within the current recommendation without even expanding those recommendations."