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June 18, 2014
Recent Flu Season Caused More Middle-Age Hospitalizations

Atlanta—How was the 2013–14 influenza season different from those that came before?

In a recent review in the Morbidity and Mortality Weekly Report (MMWR), the CDC said this was the first influenza A (H1N1)pdm09–predominant season since the emergence of the virus in 2009 and also was notable for its later-season influenza B activity.

In addition, hospitalization rates among those aged 50 to 64 years were significantly higher than in all years since the 2009 pandemic, although hospitalization rates in all other age groups—including the highest levels among patients aged 65 and older—were within the range of recent seasons.

Elevated admissions for the 50-to-64 age group were “likely attributable to several factors, including lack of cross-protective immunity to pH1N1 and lower influenza vaccination coverage among persons in this age group,” the CDC suggests.

As for good news, nearly all of the influenza virus specimens sent to CDC for antigenic characterization were found to be similar to the components of the 2013–14 Northern Hemisphere influenza vaccine. The FDA has recommended that the 2014–15 influenza vaccines used in the United States have the same antigenic composition as those used in 2013–14.

The CDC is urging that influenza surveillance, including for novel influenza viruses, should continue throughout the summer months. Health care providers are advised to consider influenza as a cause of respiratory illness even outside the typical season.

While influenza viruses typically circulate at low levels during the summer months, it is possible to be affected during that time period, according to public health experts who recommend timely empiric antiviral treatment for patients with severe, complicated, or progressive influenza illness and those at higher risk for influenza complications. Antivirals can be used for other patients, as well, as long as it is started within 48 hours of illness onset.

The MMWR article states that, during the 2013–14 influenza season in the U.S., influenza activity increased through November and December before peaking in late December. While influenza A (H1N1)pdm09 (pH1N1) viruses predominated overall, influenza B viruses and, to a lesser extent, influenza A (H3N2) viruses also were reported.

In general, the U.S. had lower levels of outpatient illness and mortality than when influenza A (H3N2) has predominated, despite the higher rates of hospitalization among adults aged 50–64 years.

Overall, the flu season’s peak occurred during surveillance week 52 (the week ending December 28, 2013) nationally but differed regionally. Influenza activity peaked first in the South around December 7, while some areas in the eastern U.S. did not reach the highest number of cases and start declining until the end of January, the CDC said. Influenza B activity occurred later in the season, however.

Emphasizing the importance of year-round influenza surveillance, the MMWR report notes that an H3N2v virus that had acquired the matrix (M) gene from pH1N1 was first identified in pigs in 2010 and, after being identified in 12 human patients in 2011, became the most commonly identified novel influenza A virus in the U.S. Cases were most often associated with prolonged direct contact with swine in agricultural fair settings, the CDC added, with limited human-to-human spread so far.

The larger H3N2v outbreaks in 2012 and 2013 in the U.S. and continued identification of influenza A (H7N9) viruses (5) and other avian influenza viruses in humans outside the U.S. underscore the importance of ongoing monitoring for novel influenza A viruses throughout the year, according to the report.





U.S. Pharmacist Social Connect