Influenza B Causes Another Spike in Flu Hospitalizations for March

The proportion of individuals visiting their doctor for influenza-like illness (ILI) has continued to drop closer to national baseline levels, according to the newest flu activity summary from the Centers for Disease Control and Prevention (CDC). In week 12 ending March 24, 2018, ILI fell from 2.8% the previous week to 2.5%; however, it remains above the 2.2% national baseline. ILI hit its peak of 7.5% this flu season during week 6. The number of states reporting widespread flu activity fell in week 12 to Puerto Rico and 16 states, while Influenza B viruses continued to have a late-season predominance, making up more than 57% of flu-positive tests.

State health officials around the country are warning the public that despite the overall drop in flu activity, influenza B is causing a “second wave” of flu illnesses for the 2017-2018 flu season. In Washington State, the Spokane Regional Health District (SRHD) is reminding area residents that the flu season isn’t over yet. While flu hospitalizations in Spokane County peaked in January, the region saw an unexpected rise in hospitalizations in March, including 63 influenza B-related hospitalizations. The county saw 6 influenza-B related hospitalizations in March 2017.

“We often see a late surge of influenza B during seasons when influenza A H3N2 was the predominant virus earlier in the season,” said SRHD health officer, Bob Lutz, MD, MPH, in a recent statement. “In the midst of already seeing higher than normal cases of influenza B, we also don't know what the influenza B wave will look like.”

Illness associated with influenza B can be just as severe as influenza A-associated illness, Dr. Lutz added. In fact, influenza B tends to be more severe for younger children. Therefore, health officials are still pushing for individuals to receive the seasonal flu shot, which has been about 42% effective against influenza B this season; they also recommend frequent handwashing to prevent the spread of the virus. In Spokane County, 67% of this season’s 37 flu deaths were among those who were unvaccinated.

In international flu news, the World Health Organization (WHO) recently reported that it was notified about a case in the Netherlands involving a child under the age of 2 years who was infected with a new seasonal reassortant A(H1N2) influenza virus. They noted that the child had not traveled abroad, was not vaccinated against the flu, did not use antiviral flu medication, and had no underlying medical conditions; the child experienced mild illness and made a full recovery. While the case is noteworthy, health officials emphasize that the case isn’t a cause for concern.

"This A(H1N2) reassortant virus is thought to pose a health risk similar to other seasonal influenza viruses,” said the CDC in a statement. “The virus has not been detected beyond this one person and current seasonal flu vaccines would likely offer protection against this virus. Additionally, this virus does not have markers associated with resistance to the neuraminidase inhibitor class of antiviral drugs, and thus should be susceptible to treatment with currently licensed and available flu antiviral medications.”