CDC Briefing on Flu: This Season Characterized as 'Challenging' and 'Intense'


In a briefing late last week, Brenda Fitzgerald, MD, director of the Centers for Disease Control and Prevention (CDC), called this year's flu season "challenging" and "intense," and reported that there have been seven more pediatric deaths reported. She noted, "The most important things to remember are, one, protect yourself from flu by washing your hands often, especially if you are caring for someone who is sick. Protect others by staying home, seeing a doctor if you are sick, and covering your mouth when you cough or sneeze. And remember it’s not too late to get a flu shot for yourself and for your child."

Daniel Jernigan, MD, MPH, director of the Influenza Division at the National Center for Immunization and Respiratory Diseases, reported that while flu activity is beginning to decrease in some parts of the U.S., it remains high for most of the country, with influenza activity in some areas still rising.

"Most people with influenza are being infected with the H3N2 influenza virus," Jernigan explained. "And in seasons where H3N2 is the main cause of influenza, we see more cases, more visits to the doctor, more hospitalizations, and more deaths, especially among older people. This season is now looking like the 2014-15 season where H3N2 predominated. That season was categorized as a high-severity season. While most people with flu will feel sick, they may miss work or school, but most will recover. However, some people will go on to have more severe illness, including hospitalizations and deaths."

Jernigan continued, "We know that flu is still happening all over the United States. We’ve experienced two notable characteristics of flu this season: The first is that flu activity became widespread within almost all states and jurisdictions at the same time. The second is that flu activity has now stayed at the same level for three weeks in a row, with 49 states reporting widespread activity, each week, for three weeks. We often see different parts of the country 'light up' at different times, but for the past three weeks, the entire country has been experiencing lots of flu, all at the same time. If we look at what is happening at doctors' offices and emergency departments, we are clearly seeing a lot of people going to see the doctor or being seen in urgent care settings. The number of people going in to see a doctor for influenza-like-illness increased again this week, rising to 6.6 percent; that means that 6.6 percent of all people coming into the clinics and emergency departments had influenza-like illness. This is the highest level of activity recorded since the 2009 H1N1 pandemic, which peaked at 7.7 percent. It looks like a big part of the late-January activity is flu transmission from kids returning to school after the holidays. Flu activity has been elevated for nine consecutive weeks so far this season. To put that into perspective, the average duration of a flu season in the past five seasons has been around 16 weeks, with the longest being 20 weeks. So, by this measure, we are about halfway there this season. That means we have several more weeks of flu to go. However, we have some signs that flu activity may have peaked in some parts of the country. California and other states on the West Coast are seeing activity begin to go down. Hospitalizations and deaths however may continue to increase, as these data are still coming in to those systems there." 

In terms of patients who are being hospitalized with influenza, for the week ending Jan. 20, 2018, the rate of hospitalizations are very similar to the 2014-15 season, according to Jernigan. "This week, we’re reporting 41.9 per 100,000 as the rate for hospitalizations. The rate is about the same as it was in 2014-15. If you go back to the 2014-15 season, for that whole season, the total amount of hospitalizations was around 710,000 so we would expect at the end of this season to have something probably around that number."

He added, "The highest hospitalization rate this season, as in most seasons, is among people 65 years and older. The second most impacted group this season are people 50-64 years of age, with a rate of 44.2 per 100,000. This represents a change from what we have seen in the last several seasons for two reasons. First, during most seasons, young children aged 0-4 years have been the next most impacted group after those of age over 65, however, this season, people 50-64 are now in that spot; in other words, baby boomers have higher rates than grandchildren right now. Second, the hospitalization rate for 50-64-year-olds this season is significantly higher than what was observed during recent seasons in 2012-13 and 2014-15. When we look at actually what are those influenza viruses that are sending these 50-64-year-olds to the hospital this season, we see that not only is it H3N2 but also the other influenza A virus H1N1 that is contributing to these higher rates. For the younger age groups, the hospitalization rates are either similar to or lower than observed during recent more severe seasons."

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