‘Mixed bag’ flu season has been particularly tough on children
For the first time in 27 years, influenza B viruses have predominated in the United States, accounting for more than 56% of samples tested in public health laboratories as of Jan. 18, according to CDC data.
Influenza B viruses are more common in children than adults, which potentially explains some incongruities in U.S surveillance data, according to Lynnette Brammer, MPH, who leads the CDC’s domestic influenza surveillance team.
CDC data showed that the percentage of outpatient visits for influenza-like illness increased from 4.7% to 5% for the week ending Jan. 18, after declining sharply for 2 weeks in a row. CDC estimates showed a cumulative rate of influenza-related hospitalization of 24.1 per 100,000 people, not out of line with previous seasons. The rate of deaths attributed to pneumonia or influenza declined slightly in the week ending Jan. 18, from 7.1% to 6.7%, remaining below the epidemic threshold.
Brammer called the season a “mixed bag.”
“Influenza B — particularly the B Victoria [viruses] that are out there — don't tend to impact the elderly very much. But they do impact kids, particularly school-age kids,” Brammer told Healio. “Our influenza-like illness graph looks like it was a bad season — it's pretty high at the peak. But if you look at the hospitalizations and the pneumonia and influenza mortality, that's not very remarkable, and that's because the people that tend to get hospitalized and die from influenza in the largest numbers are the elderly.”
Brammer suggested the uncommon predominance of influenza B viruses may be explained by the lack of circulating B viruses in previous seasons, particularly of the B/Victoria lineage, which have accounted for almost all influenza B specimens tested this season.
“The Victorias have been changing, and I think it got to the point to where there wasn't a lot of population immunity to them,” Brammer said.
The CDC reported an additional 15 pediatric influenza deaths for the week ending Jan. 18, raising the seasonal total to 54. There were 143 influenza-related pediatric deaths in the U.S. last season.
Bernhard L. “Bud” Wiedermann, MD, MA, attending physician in infectious diseases at Children’s National Hospital in Washington, D.C., and professor of pediatrics at The George Washington University School of Medicine & Health Sciences, said his hospital was “clearly still in the midst of a very busy flu season.” He wondered if there would be a second peak attributed to influenza A.
“We will need to continue to be prepared as best we can, knowing that any season can contain surprises,” he told Healio.
Overall, the CDC estimated that 15 million to 21 million influenza-related illnesses and 7 million to 10 million influenza-related medical visits occurred as of Jan. 18. In addition, it estimated there were 140,000 to 250,000 influenza-related hospitalizations and 8,200 to 20,000 influenza-related deaths.
“The critical message has to still be vaccinate, vaccinate, vaccinate,” Infectious Diseases Society of America spokesperson Aaron E. Glatt, MD, professor of medicine at Mount Sinai’s Icahn School of Medicine and chair of medicine at Mount Sinai South Nassau in Oceanside, New York, told Healio. “When you get vaccinated, you're not only helping yourself, you're also preventing everybody else around you from getting sick — and it's not too late to get vaccinated.”
Brammer said the CDC would have preliminary estimates of the effectiveness of the 2019-2020 influenza vaccine in the coming weeks.
“Flu is going to be a much bigger killer in the United States than this coronavirus and people aren't doing everything that they possibly can to diminish the spread,” Glatt said. – by Eamon Dreisbach
CDC. Weekly U.S. Influenza Surveillance Report. https://www.cdc.gov/flu/weekly/index.htm/. Accessed January 27, 2020.
CDC. 2019-2020 U.S. Flu Season: Preliminary Burden Estimates. https://www.cdc.gov/flu/about/burden/preliminary-in-season-estimates.htm. Accessed January 27, 2020.
Disclosures: Brammer and Glatt report no relevant financial disclosures. Wiedermann reports receiving honoraria from Best Doctors, The Emmes Company and MeMed Diagnostics.