Last week, Dr. Margaret Chan, head of the World Health Organization, announced that the virus is still considered pandemic, meaning widespread, although case numbers have ebbed considerably. In the United States, the CDC reported that, as of May 22, just 1 percent of outpatient visits involved flu. However, this new H1N1 flu, long ago pushed aside prior seasonal flu viruses to become the dominant strain. And experts believe it will settle into the regular fall/winter outbreak pattern that people are used to.
Experts noted that this type of major viral shift occurs every few decades with influenza. “What most people are expecting is that [the new H1N1 strain] will supplant the older H1N1 viruses that were the previous seasonal strains and become the seasonal H1N1 virus,” explained Dr. John J. Treanor, professor of medicine and of microbiology and immunology at the University of Rochester Medical Center in New York. “The most likely scenario would be that we would continue to see the descendants of pandemic H1N1 causing seasonal outbreaks of flu, with probably normal timing,” he said.
So H1N1 pandemic flu will — like prior dominant flu strains — probably mount a resurgence this fall and wane again in the spring of next year. That’s the polar opposite of how it first appeared on the scene in the spring of 2009.
According to the World Health Organization, H1N1 flu is currently most active in areas of the Caribbean and Southeast Asia, although cases remain relatively low, Agence France-Presse reported. WHO based its announcement Thursday on a report from a 15-member panel of experts. That committee will meet again in July when more data arrives on the progress of flu during the southern hemisphere’s winter season.
Since it first appeared, H1N1 — which had killed 12,000 Americans by the end of March, according to CDC estimates — has distinguished itself from the “regular” flu in several ways.
- It has tended to strike harder at children and younger adults than at the elderly, who were the most likely to succumb to previous seasonal flu strains. That could be because older people picked up some immunity in their youth from prior, related H1N1 outbreaks.
- Pregnant women, especially, were endangered from the H1N1 strain. In a study published in April in the Journal of the American Medical Association, CDC researchers found that while pregnant women make up about 1 percent of the U.S. population at any given time, during the 2009 H1N1 swine flu outbreak they made up 5 percent of deaths.
- Compared to prior seasons of “regular” flu, H1N1 actually caused milder disease and fewer deaths overall. (The conventional seasonal flu typically kills about 36,000 Americans every year.) That might remain the case in the near future, experts said, but changes to the H1N1 virus and those most affected could occur over time.
- Less illness and fewer deaths among the elderly and overall are a good thing, but more mortality among the young means more years of life lost, Treanor pointed out.