March 4, 2015
Influenza B Virus Increasing; Good Vaccine Match

Atlanta—While influenza activity is still elevated across the United States, although it continues to decrease, the CDC warns that an increase in influenza B viruses has been detected in some areas.

According to the CDC’s latest FluView report, during the week ending February 14th, 77% of the influenza-positive tests reported to the CDC were influenza A viruses and 23% were influenza B viruses. Of the 518 influenza A viruses that were subtyped, 98.8% were influenza A (H3) viruses and 1.2% were influenza A (H1N1) pdm09 viruses.

About half of the H3N2 flu viruses analyzed so far this influenza season are drift variants—viruses with antigenic or genetic changes that make them different from the viruses for which the season’s vaccine offers maximum protection. The B viruses appear to be a good match, however, to the vaccine used this season, the CDC reported.

As in recent past seasons, high levels of resistance to the adamantanes—amantadine and rimantadine—continue to persist among influenza A (H1N1)pdm09 and influenza A (H3N2) viruses, according to public health officials who emphasized that adamantanes are not effective against influenza B viruses.

Antiviral drugs approved for influenza include the neuraminidase inhibitors oseltamivir and zanamivir as well as Rapivab (peramivir), which was approved in December. The CDC said that the influenza A and B samples tested generally have been sensitive to neuraminidase inhibitors, although one H1N1 virus showed some resistance to oseltamivir and peramivir.

Although the average length of a flu season for the past 13 seasons has been 13 weeks, that threshold already has been reached this year and flu activity is expected to continue longer than usual.

For this influenza season overall, the hospitalization rate in patients 65 years and older is 242.2 per 100,000, the highest recorded since data collection on laboratory-confirmed influenza-associated hospitalization in adults began during the 2005-2006 season. This is the highest rate of any age group. Previously, the highest recorded hospitalization rate was 183.2 per 100,000 in the 2012-2013 season, which was the last H3N2-predominant season.

U.S. Pharmacist Social Connect