Despite progress on the flu front, work still needed

CDC. MMWR. 2011;60:705-712.

Issue: July 2011

The bulk of influenza-related morbidity and mortality has now shifted back to older people for the 2010-2011 influenza season, according to the latest CDC and WHO data.

Influenza activity for the 2010-2011 season peaked in early February and influenza A (H3N2) virus predominated. A total of 246,128 specimens were tested for influenza, of which 54,226 were positive (22%) and at least 311 deaths related to influenza, according to CDC and WHO.

Influenza A predominated

The report summarized the influenza season from Oct. 3 to May 21. Health officials reported that although influenza A (H3N2) remained the predominant virus throughout the season, the pandemic 2009 influenza A (H1N1) strain and influenza B viruses continued to circulate and dominate in certain areas.

“Of the 105 deaths, 40 were associated with influenza B viruses, 27 with 2009 influenza A (H1N1) virus, 18 with influenza A (H3N2) viruses, and 20 with influenza A virus for which the subtype was not determined,” the researchers wrote. They added that during the 2009-2010 pandemic, 348 pediatric deaths were reported between April 15, 2009, and Oct. 2, 2010. This was a significant increase from the 2008-2009 season, during which 67 influenza-associated pediatric deaths were reported, and the year before, when 88 deaths were reported.

Using FluSurv-NET surveillance data, health officials calculated the cumulative hospitalization rate (per 100,000 population) for this season and said the rate was “10.7 among adults aged 18-49 years, 21.7 among adults aged 50-64 years, and 62.5 among adults aged 65 years and older,” which was similar to rates in 2007-2008.

According to the Morbidity and Mortality Weekly Report, there were five cases of human infection with swine-origin influenza A (H3N2) viruses. Two cases occurred in September in Pennsylvania and Wisconsin, one case in October in Pennsylvania, and two cases in November in Minnesota, according to health officials, who added that most of these patients had either direct or indirect contact with swine.

Next year’s vaccine

The researchers said the FDA’s Vaccines and Related Biological Products Advisory Committee has recommended keeping the same three influenza strains in the 2011-2012 influenza vaccine that are in the current season’s vaccine, which are A/California/7/2009 (H1N1)-like virus, A/Perth/16/2009 (H3N2)-like virus, and the B/Brisbane/60/2008-like virus.

Summarizing their report, the health officials wrote, “In comparison with the past three seasons, the 2010-2011 influenza season was less severe than the pandemic year and the 2007-08 season, but more severe than the 2008-09 influenza season, as determined by the percentage of deaths resulting from pneumonia or influenza, the number of influenza-associated pediatric deaths reported, and the percentage of visits to outpatient clinics for influenza-like illness.”

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