Flu Shot No Match for 'B' Strain, Season Rages On

From the WebMD Archives

Jan. 16, 2020 -- Influenza is still going strong in the United States and isn't expected to slow down for at least several more weeks, according to a report from the CDC.

What's more, this season's vaccine is only a 58% match for the B strain of flu, known as B/Victoria, that is hitting children especially hard.

"It's not a very good match for B/Victoria," Anthony Fauci, MD, director of the National Institute of Allergy and Infectious Diseases, told CNN. "It's not an awful match, but it's not a very good match."

Nationally, the predominant virus is B/Victoria, followed by A(H1N1)pdm09 viruses, with the dominant virus varying by region and age group. Other strains of A and B have been seen in low numbers.

"Key indicators that track flu activity remain high, but indicators that track severity are not high at this point in the season," the CDC says in the report.

Although levels of outpatient hospital visits for influenza-like illness (ILI) remain high, hospitalization rates and the percentage of deaths from pneumonia and influenza are low so far.

"This is likely due to the predominance of influenza B/Victoria and influenza A(H1N1)pdm09 viruses, which are more likely to affect children and younger adults than the elderly. Because the majority of hospitalizations and deaths occur among people age 65 and older, with fewer illnesses among that group, we expect, on a population level, to see less impact in flu-related hospitalizations and deaths," the CDC says.

Outpatient visits for ILI activity fell from 7% the previous week to 5.8%.

Regionally, the percentage of outpatient visits for flu ranged from 3.6% to 8.6%, with all regions reporting a high level of outpatient visits.

ILI activity was high in the District of Columbia, New York City, Puerto Rico, and 33 states; moderate in six states (Alaska, Indiana, Michigan, Minnesota, Rhode Island, and South Dakota); and low in eight states (Florida, Hawaii, Missouri, Montana, Nevada, Ohio, Vermont, and Wyoming).

Hospitalizations and Deaths

According to the CDC's estimates, there have been at least 9.7 million illnesses, 87,000 hospitalizations, and 4,800 deaths from flu this season.

The overall hospitalization rate was highest for people 65 or older (33.3%), followed by children younger than 5 (26.8) and those 50 to 64 years old (17.0).

The percentage of deaths from pneumonia and influenza edged up to 5.8%, short of the 6.9% threshold to declare an epidemic.

During the first week of this year, the CDC received reports of five flu-associated deaths of children. Three of those were linked to influenza B viruses, and two were related to influenza A.

So far, the CDC has received reports of 32 flu-related deaths of children this season, compared with 16 at this point last season. Twenty-one of this season’s deaths were related to influenza B viruses, and 11 were linked to influenza A.

Influenza B viruses can cause severe illness in adults and children. But adults often have built up immunity from previous infections, and children may not have.

Influenza A viruses can also cause serious illness in adults and children. The CDC recommends vaccination for everyone aged 6 months or older and antiviral medications as soon as possible after getting the flu.