Influenza B Making a Surge in the United States


Influenza A (H3N2) has caused most of the illnesses in this severe flu season, but influenza B is becoming increasingly responsible for more infections as the flu season continues to hit the United States.

While influenza A viruses, particularly H3N2, have caused the majority of illnesses in the severe flu season of 2017-2018, health officials are reporting a nationwide rise in influenza B viruses, which can lead to some catching the flu twice in the same season.

In the FluView report for week 5 ending on February 3, 2018, the Centers for Disease Control and Prevention (CDC) reported that more than 30% of laboratory-confirmed flu-positive respiratory specimens were influenza B viruses. That’s well above this season’s average of about 20%, and reflects what the CDC says is an increasing proportion of influenza B and H1N1 viruses being detected nationally. In a press briefing on February 9, CDC acting director Anne Schuchat, MD, RADM, USPHS, explained that it’s not uncommon to see a second wave of influenza B activity during an influenza season, and noted that the flu vaccine actually offers better protection against B viruses than it does against influenza A (H3N2), the predominant virus that has caused such a severe flu season this year.

During week 5, the CDC reported that 10.1% of all deaths in the country were attributed to pneumonia and influenza. In addition, the proportion of individuals visiting outpatient health care providers for influenza-like illness rose to 7.7%, a level last achieved during the flu pandemic of 2009. Still, Dr. Schuchat noted that this flu season is not yet being called a pandemic, despite its severity.

The CDC also reported 10 more influenza-associated pediatric deaths, 7 of which were associated with influenza A viruses and 3 of which were associated with influenza B viruses. With 63 pediatric flu deaths and still many weeks left in this flu season, the CDC continues to recommend flu vaccination for everyone 6 months of age and older who is healthy enough to receive a flu shot. Health officials are also reminding clinicians to promptly treat flu patients — particularly young children and those who are who are at high risk of serious flu complications – with antiviral medications.

Meanwhile, on February 9, 2018, New York City’s Department of Health and Mental Hygiene reported the city’s third pediatric flu death this season but did not release any other details about the child. Then, 2 days later, the death of a 5-year-old girl in Brooklyn was being called a possible fourth pediatric flu death in the city. The child had experienced flu-like symptoms including fever and difficulty breathing. Her death is under investigation by New York City health officials. New York City has reported more than 4,200 flu-positive respiratory samples as of week 4.

“We need to work together to stop the spread of the flu. Young children, seniors and anyone with underlying health conditions are particularly at risk,” wrote New York City mayor Bill de Blasio in a tweet following the news of the death. “Call 311 for information on how you can still get a flu shot, and contact a doctor immediately if you feel ill.”

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