CDC Officials Note Slow Start to Flu Season

With the flu season underway in the United States, new surveillance data shows that influenza activity has been slowly increasing nationally since starting low in October.

The Center for Disease Control’s (CDC) weekly FluView report details national influenza activity in the United States, particularly in the peak flu season months from October through May. So far this season, the World Health Organization and National Respiratory and Enteric Virus Surveillance System (NREVSS) clinical and public health laboratories from all 50 states have collected respiratory specimens, tested them for influenza and reporting all findings to the CDC. Of the more than 200,000 specimens tested so far this season, at least 7,131 have been positive for influenza, with nearly 77% of those coming up positive for influenza type A viruses and 23% positive for influenza type B viruses.

The circulating strains detected so far by national surveillance are highly antigenically similar to virus components in the 2016-2017 flu vaccine.

According to the CDC’s recent Morbidity and Mortality Weekly Report, of the 1,824 influenza A specimens subtyped in public health laboratories, 95 (5.2%) were influenza A (H1N1) pdm09 and 1,729 (94.8%) were influenza A (H3N2). Of the 97 influenza B viruses with lineage determined, 39 (40.2%) were of the B/Yamagata lineage and 58 (59.8%) were of the B/Victoria lineage. In Iowa, the state health department reported one human infection with a novel influenza A (H1N2) variant.

The most widespread flu activity so far this season has been in California, New Hampshire, New York, North Carolina, Oklahoma, Oregon, Pennsylvania, Virginia, and Guam. From October 1, 2016 through December 24, 2016, there have been 863 laboratory-confirmed influenza-associated hospitalizations reported in the United States with the highest rate of hospitalizations occurring in individuals aged 65 and older. Of those hospitalizations, 733 (84.9%) were associated with influenza A virus, and more than 98% of those cases with subtype information had influenza A (H3N2).

The CDC notes that flu seasons predominated with illnesses from influenza A (H3N2) viruses tend to be more severe overall than seasons high in influenza A (H1N1) activity, and so far this season the United States has experienced more cases of influenza A (H3N2). Although CDC officials recommend that everyone 6 months and older receive the flu vaccine by the end of October to prevent getting sick this season, as of early November of 2016, about 60% of the US population still had not received the seasonal flu shot. According to the CDC, vaccination can continue throughout the season, even after January, and so it is not too late.

Along with the flu vaccine, the influenza neuraminidase inhibitor antiviral medications oseltamivir, zanamivir, and peramivir are also important weapons during the flu season. Recent epidemiological testing of 205 influenza virus specimens collected this season showed low resistance to the antiviral medications, suggesting that these medications will offer effective treatment to those who do become ill this flu season.