CDC: ILI activity high across the South and in Puerto Rico

ATLANTA — For the second week, influenza-like activity tracked above the national baseline, according to the Weekly U.S. Influenza Surveillance Report released by the Centers for Disease Control and Prevention on Friday, indicating that this year's season is officially underway. The trajectory of illness rates are tracking ahead of the past two years, which suggests this season has the potential to be a severe season. 

 

Already, Puerto Rico and six states — Alabama, Florida, Georgia, Louisiana, Mississippi and Texas — are experiencing high ILI activity. Illinois has reported moderate ILI activity.  The CDC last week issued a public health advisory even though influenza activity is presently low in the United States as a whole.



"This season, influenza A (H3N2) viruses have been reported most frequently and have been detected in almost all states," the agency stated. "During past seasons when influenza A (H3N2) viruses have predominated, higher overall and age-specific hospitalization rates and more mortality have been observed, especially among older people, very young children, and persons with certain chronic medical conditions compared with seasons during which influenza A (H1N1) or influenza B viruses have predominated."

 

Almost half (48%) of the influenza A (H3N2) viruses collected and analyzed in the United States from Oct. 1 through Nov. 22, 2014 were antigenically "like" the 2014-2015 influenza A (H3N2) vaccine component, but that 52% were antigenically different (drifted) from the H3N2 vaccine virus. In past seasons during which predominant circulating influenza viruses have been antigenically drifted, decreased vaccine effectiveness has been observed. 

 

However, vaccination has been found to provide some protection against drifted viruses. Though reduced, this cross-protection might reduce the likelihood of severe outcomes such as hospitalization and death. In addition, vaccination will offer protection against circulating influenza strains that have not undergone significant antigenic drift from the vaccine viruses (such as influenza A (H1N1) and B viruses).

 

Because this year's vaccine can still provide some protection, the CDC last week advised people to get their flu shots if they haven't done so already.