Overall, flu activity in the U.S. remains low and is down significantly from the late fall peak. However, the percentage of specimens testing positive for influenza B has risen in recent weeks.
Three notes:
- Influenza A strains drove most cases since flu activity began increasing in October. CDC data indicates emergency department visits and hospitalizations for COVID-19, flu and respiratory syncytial virus peaked in early December. After that, flu metrics continued to decline week over week.
- Just under 1 percent of more than 66,000 specimens tested for influenza at clinical laboratories in the U.S. were positive for the week ending March 25, according to the CDC's latest FluView report. Of the 626 specimens positive for flu, about 38 percent were positive for influenza B. Before that, influenza B was accounting for a much smaller percentage of positive specimens, CDC data shows.
- It's not unusual to see an influenza B resurgence after influenza A peaks, and it is an indicator of a return to normal respiratory virus season patterns, according to experts.
"We have to remember that, overall, we're returning to a somewhat normal respiratory virus season," John Brownstein, PhD, epidemiologist and chief innovation officer at Boston Children's Hospital, told ABC News in an April 5 report. "Influenza B is often later in the season … it's not a surprise at all that we're seeing flu B and, as part of our turn to normal, we have to remember that flu still has an impact on population health."