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‘Flu is everywhere’: CDC notes severe but not unprecedented activity
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The rate of influenza-related hospitalizations in the United States nearly doubled in just 1 week as the country deals with a severe but not unprecedented influenza season that is being dominated by a strain associated with reduced vaccine effectiveness and serious illness, CDC officials said.
“Flu is everywhere in the U.S. right now. There’s lots of flu in lots of places,” Daniel B. Jernigan, MD, MPH, director of the CDC’s Influenza Division, said today in a teleconference.
According to the most recent CDC data, there were 22.7 laboratory-confirmed hospitalizations associated with influenza per 100,000 people in the U.S. in the week ending Jan. 6, up from 13.7 the previous week. According to Jernigan, the highest rates of hospitalizations are among patients aged 65 years and older. Influenza is also heavily affecting baby boomers aged 50 to 64 years and young children. The CDC reported seven more influenza-associated pediatric deaths, raising the total to 20 for the season.
The results are typical for a season dominated by influenza A(H3N2) — a strain notorious for evading the seasonal vaccine and which is often linked to more severe illness. According to CDC data, H3N2 remains the most prevalent circulating strain this season.
“When H3N2 are predominant, we tend to have a worse flu season with more hospitalizations and more deaths,” said CDC Director Brenda Fitzgerald, MD.
The current season started early and is probably peaking right now, Jernigan said, though there may be another few months of influenza activity remaining. In terms of severity and timing, it resembles two other recent seasons dominated by H3N2 viruses: 2012-2013 and 2014-2015.
In a health advisory issued last month, the CDC reminded clinicians that influenza should be high on their list of possible diagnoses for ill patients. Jernigan said clinicians should not wait to treat patients with antivirals, which work better the earlier they are taken. The CDC recommends all hospitalized patients and any high-risk patients — such as those aged younger than 2 years or older than 65 years — with suspected or confirmed influenza be treated as soon as possible with antiviral medications.
So far, every U.S. state except Hawaii and the District of Columbia has seen widespread influenza activity by now — the first time in 13 years since the agency has been doing this type of surveillance that practically the entire continental U.S. has experienced such activity at the same time, Jernigan said.
CDC data show that much of the U.S. is experiencing influenza activity at the highest level, including most states in the South, Midwest and West. The proportion of outpatient visits for influenza-like illness rose slightly to 5.8% in the week ending Jan. 6, closing in on the 6% rate seen in 2014-2015.
“We are currently in the midst of a very active flu season, with much of the country experiencing widespread and intense flu activity,” Fitzgerald said.
According to the CDC, 12.8% of the 371,863 specimens tested in clinical laboratories as of Jan. 6 were positive for influenza, including 82.9% that tested positive for influenza A. Among influenza A viruses that were subtyped by public health laboratories, 89.9% were H3N2 viruses.
The CDC recommends, with few exceptions, that everyone aged 6 months and older receive a seasonal influenza vaccination. Recent data showed that the H3N2 component of the vaccine was just 10% effective in Australia — raising concerns about the Northern Hemisphere’s vaccine, which uses the same H3N2 strain. But Vivien G. Dugan, PhD, deputy chief of the Virology, Surveillance and Diagnosis Branch in the CDC’s Influenza Division, told Infectious Disease News in December that last year’s vaccine performance against H3N2 is likely to be a better barometer for how it will perform this season.
The same H3N2 vaccine strain was 32% effective last season — only slightly lower than the overall vaccine effectiveness of 39%. Jernigan said vaccine effectiveness estimates for this season will not be available until at least mid-February.
Most influenza vaccines protect against four strains — two influenza A viruses, H3N2 and H1N1, and two B viruses. A recent editorial by National Institute of Allergy and Infectious Diseases Director Anthony S. Fauci, MD, and others in the New England Journal of Medicine has stoked interest in a universal influenza vaccine that would be long-lasting and widely protective — a longtime goal of researchers.
Until such a vaccine exists, however, Fitzgerald said seasonal influenza vaccination remains the best way to prevent infection. She said manufacturers have reported shipping more than 151 million doses of seasonal vaccine so far this season.
“It’s not too late to get one,” she said. “It should be readily available.” – Gerard Gallagher
References:
CDC. FluView. https://www.cdc.gov/flu/weekly/index.htm. Accessed January 12, 2018.
Paules CI, et al. N Engl J Med. 2018;doi:10.1056/NEJMp1714916.
Disclosures: Fitzgerald and Jernigan report no relevant financial disclosures.