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Nov./Dec. 2009
Vol. 19 No. 11
Annual Meeting Coverage
Updates on H1N1 and Seasonal Influenza
Ed Susman

In the midst of a challenging influenza season, clinicians and researchers shared information about the current understanding of—and response to—the novel 2009 H1N1 strain, as well as findings related to seasonal influenza, during a series of presentations at the 47th Annual Meeting of IDSA.

Sylvie Briand, MD, MPH, PhD, acting director of  the Global Influenza Programme of the World Health Organization (WHO), reported that H1N1 manifests in a wide spectrum of infection from cases without symptoms to fatal disease. “Most people develop self-limited upper respiratory illness,” she said, but groups at higher risk for severe disease include pregnant women; individuals with chronic respiratory and cardiovascular diseases; people with diabetes; and those who are immunosuppressed.

Bacterial co-infection, namely with pneumococcus and Staphylococcus aureus, is more frequently reported than initially recognized, especially in severe rapidly progressing disease, Dr. Briand said during an H1N1 symposium. “Timely antiviral treatment has gained evidence in reducing severe illness and death,” she said.

Antivirals should be used, ideally early, and at any stage of active disease when ongoing viral replication is observed, she said. However, due to reports of resistance developing to oseltamivir, chemoprophylaxis against influenza has not been recommended.

Strikingly, researchers have observed, very elderly individuals appear to be resistant to the latest H1N1 strain, and James E. Crowe Jr., MD, FIDSA, professor of pediatrics, microbiology, and immunology at Vanderbilt University Medical Center in Nashville, Tenn., thinks he knows why.

Antibodies induced by the devastating 1918 influenza pandemic are still found in potent levels among people in their 90s and even those older than 100 years, he said. “The 2009 H1N1 hemaglutinin possesses what are essentially some of the 1918 hemaglutinin antigenic sites, thus facilitating cross-reactive immunity of elderly antibodies to both the early 20th century flu viruses and the 2009 pandemic virus.”

In the United States, Stephen Redd, MD, director of the Influenza Coordination Unit at the Centers for Disease Control (CDC), outlined the pillars of attack against influenza – either seasonal or H1N1 – which are based on enhanced surveillance, vaccination, state and local support, medical care and countermeasures, community mitigation measures, and communication though the media. He also noted the Food and Drug Administration’s (FDA) decision in October to allow for the emergency use of the investigational intravenous antiviral paramivir for the treatment of influenza.

The current response to H1N1 has been marked by a lesser than expected supply of vaccine, at least initially. But even when vaccine is available, motivating people to get immunized against influenza is not always easy, said Bruce G. Gellin, MD, MPH, deputy assistant secretary for health and director of the National Vaccine Program Office at the U.S. Department of Health and Human Services. While polling suggests worries about catching influenza have increased, from 39 percent of respondents expressing such concerns in August 2009 to 51 percent in October 2009, Dr. Gellin said health care professionals still have to deal with those who avoid influenza vaccination.

The government’s goal is “to vaccinate as many persons as quickly as possible,” Dr. Gellin said. “During initial limited availability, the goal is to target those at higher risk for influenza-related complications and infections.” He also noted recommendations encouraging local flexibility and decision-making for expanding the target to larger population groups.

While H1N1 may currently be generating more attention, seasonal influenza remains a concern and “causes a substantial disease burden,” said Kathleen Neuzil, MD, PhD, an associate professor of medicine at the University of Washington, in a symposium on seasonal influenza.” She noted that vaccination rates for influenza remain low for a number of reasons, including public perception that influenza isn’t a serious disease. Efforts are being made to improve production of vaccines to make them easier to produce and more effective, she said.

One problem with seasonal influenza appears to be resistance to M2 inhibitors and/or neuraminidase inhibitor oseltamivir, said Larisa Gubareva, MD, PhD, with the influenza division at CDC’s National Center for Immunization and Respiratory Diseases. To combat seasonal influenza, researchers will need to develop new antivirals and combinations of antiviral medications. “We also need enhanced surveillance and improved methods for drug resistance monitoring,” she said. In addition, Dr. Gubareva cited a need to determine the clinical relevance of laboratory-detected resistance of antiviral medications.

Audio and synchronized speaker slides from sessions at the 2009 IDSA Annual Meeting are available for purchase online.
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