Though flu season is not yet over, a number of flu indicators are tracking at the same levels as the 2014-2015 season — the last ‘high severity’ flu season on record, CDC researchers reported.
In a conference call with the media, CDC influenza division director Dan Jernigan, MD, went over the most recent FluView data, which revealed that influenza-related deaths topped the epidemic threshold, jumping up to 9.1% of all deaths.
The overall rate of hospitalizations (41.9 per 100,000 most recently) is also tracking at the same rate as 2014-2015, although there have been more hospitalizations for those under age 65. At the end of the 2014-2015 season, the CDC estimated 34 million Americans got the flu, 16 million went to a doctor’s office for it and 710,000 were hospitalized.
“We may go over the 2014-2015 season, but it’s a little hard to say at this point,” Jernigan said.
There were an additional seven pediatric influenza-associated deaths reported this week, with “some reports” indicating that number may increase next week, as well. Although CDC researchers acknowledged those figures may be higher than reported, as it does not account for deaths occurring out of the hospital. In 2014-2015, 148 pediatric deaths were reported.
This week’s data found the percentage of patients who went to see a doctor about the flu ticked up to 6.6%. It is the highest level of activity recorded since the 2009 pandemic year, which peaked at 7.7%, CDC researchers said.
One notable difference about this flu season is its proportionately more severe impact on “Baby Boomers,” those ages 50 to 64, who have the second highest rate of hospitalizations (44.2 per 100,000 in the most recent data) after adults age ≥65 (183.1 per 100,000). Usually, children ages 0 to 4 have the second highest rate of hospitalization.
“Baby Boomers have higher rates than their grandchildren right now,” Jernigan said. “But younger age groups have similar or lower rates of hospitalization than observed in recent severe flu seasons.”
He added that in addition to the H3N2 strain that has been getting all the press, the H1N1 strain is contributing to higher rates of hospitalization in this age group, and that this group “may be a little more susceptible to H1N1 infection.”
Geographic spread of flu is different this year, Jernigan added, as flu activity became “widespread” within all states and jurisdictions at the same time, and flu activity stayed at the same national level for three weeks in a row. In the most recent data, 49 states reported “widespread” flu activity. He cited regional differences in the flu, suggesting that it may have peaked in certain areas of the country, but that hospitalizations and death rates may still increase.
This is also the second consecutive year where the H3N2 strain has been predominant. Jernigan said that they have seen “some drift, but not significant drift to suggest what we’re seeing this year.”
“Either a number of folks are getting infected who didn’t get infected last year, or it’s some change in the virus we’ve not been able to detect yet,” he said. “But it’s a very human-adapted virus … and that may be impacting vaccine effectiveness.”
CDC has not yet released official vaccine effectiveness numbers for this season, but officials continued to encourage all adults and young children to get the flu shot.
Though flu activity has been elevated for nine consecutive weeks, CDC researchers estimated that an average flu season lasts 16 weeks, and some have lasted as long as 20 weeks, so this means “several more weeks of flu to go.”