A particularly severe influenza season in the United States continued to lose momentum entering March, with illnesses declining for a third straight week. But the rate of cumulative hospitalizations due to influenza reached the highest rate since at least 2010 and pediatric deaths attributed to influenza surpassed 100, according to CDC data.
Influenza activity was widespread in 45 states in the week ending Feb. 24, down from 48 the previous week. And the percentage of outpatient visits attributed to influenza-like illness (ILI) sunk to 5%, declining for a third week in a row after peaking in early February at a level equal to the height of the 2009 pandemic.
But the cumulative rate of laboratory-confirmed hospitalizations for influenza climbed to 81.7 per 100,000 people — above the highest rates documented in 2014-2015, which the CDC has used as a recent benchmark for severe influenza seasons. During the same week that season, the rate was 55.9 per 100,00 people. It topped out at 64.2 at the end of the season.
“It’s a large number,” CDC spokeswoman Kristen Nordlund told Infectious Disease News. “That number is always going to go up, no matter what, until the end of the season, when it levels off.”
Outpatient visits for flu declined for a third consecutive week, according to the CDC.
Experts have been articulating the need for a better influenza vaccine for some time, but grim surveillance statistics and poor vaccine performance this season have brought wider attention to the issue.
Amid more calls for better protection, the National Institute of Allergy and Infectious Diseases has published a detailed plan for developing a universal influenza vaccine.
Anthony S. Fauci
According to NIAID Director Anthony S. Fauci, MD, the plan identifies fundamental scientific questions critical to developing an influenza vaccine that offers broader and longer lasting protection. Scientists said the vaccine should be at least 75% effective, protect against groups I and II influenza A viruses and provide protection that lasts at least 1 year.
H3N2, an elusive influenza A virus, has been the main culprit in this season’s reduced vaccine effectiveness, with early CDC estimates showing the vaccine has been just 36% effective overall, and only 25% effective against H3N2.
H3N2 remained the predominant strain in the U.S., but a late-season surge in influenza B has continued, with the percentage of specimens tested in clinical labs that were positive for B viruses rising from 41.8% to 45.8%. Another marker, the proportion of all U.S. deaths attributed to influenza or pneumonia, ticked down again from 9.5% to 9% but remained high.
The CDC reported 17 more influenza-associated pediatric deaths, bringing the total to 114 this season. – by Gerard Gallagher
CDC. FluView. https://www.cdc.gov/flu/weekly/index.htm. Accessed March 2, 2018.
Disclosures: Fauci and Nordlund report no relevant financial disclosures.