Influenza Sending Record Number of Seniors to the Hospital

January 30, 2015

Is influenza tough this year?

It's sending a record number of seniors to the hospital, the Centers for Disease Control and Prevention (CDC) said today.

For the week ending January 24, the number of hospitalizations associated with a laboratory-confirmed case of influenza for adults aged 65 years or older was a cumulative 198 per 100,000 population since the flu season began last fall, the CDC said in its weekly FluView summary. A CDC spokesperson said that number was the highest since the agency began tracking influenza-related hospitalizations among adults in the 2005-2006 season.

The previous high occurred in the 2012-2013 season, when the hospitalization rate for this demographic was 183 per 100,000.

Influenza almost always hits the elderly harder than most, but this year's spike in hospitalizations reflects two other factors. The predominant flu virus in the 2014-2015 season — as well the 2012-2013 season — is the A(H3N2) strain, which is especially virulent. In addition, this year's trivalent flu vaccine is only 23% effective against A and B influenza viruses overall, considerably down from previous years. The reason is that two thirds of the A(H3N2) viruses in circulation have genetically drifted from the A(H3N2) strain used in the vaccine, weakening the match. Against the A(H3N2) virus, the flu vaccine is 22% effective, and this rate drops to 14% for adults aged 50 years or older.

CDC Continues to Promote Antivirals, Doubted by Some

Despite hospitalizations among the elderly hitting a new high, this year's influenza season appears to be on the wane, at least according to one measure. The percentage of outpatient visits for influenza-like illness (think fever, cough, and sore throat) has fallen from a peak of 5.9% for the week ending December 27, 2014, to 4.4% for the week ending January 10, according to FluView.

The CDC is not letting down its guard, however. Yesterday, it issued a letter to clinicians urging them to treat patients promptly with antiviral drugs when they suspect influenza, without any confirmatory testing. The letter, cosigned by leaders of the American Medical Association, the American Academy of Family Physicians, and other professional societies, noted that influenza activity across the nation remains "high overall and is likely to continue for weeks."

The letter touted the potential of antiviral drugs to reduce influenza symptoms, prevent serious complications, and keep high-risk patients out of the hospital.

Not everyone, however, agrees with the CDC's recommendation to prescribe these drugs. Some clinicians cite a Cochrane systematic review of clinical trials published in the BMJ last year that cast doubt on the effectiveness of oseltamivir (Tamiflu, Roche) and zanamivir (Relenza, GlaxoSmithKline), two of the three FDA-approved influenza antivirals on the market. The third antiviral, peramivir (Rapivab, BioCryst), was approved last month.

The Cochrane review concluded that oseltamivir and zanamivir reduced the duration of symptoms in adults by less than a day. Furthermore, oseltamivir did not decrease the number of hospitalizations (this information was not available in the zanamivir studies reviewed). Oseltamivir increased the risk for nausea and vomiting when used to treat influenza, and the risk for headaches and renal and psychiatric problems when used to prevent influenza, according to the Cochrane review. Zanamivir did not come with this side-effect baggage.

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