'We hate H3N2': 3 reasons this year's flu season could get worse

Public health officials said this week the 2017-18 flu season is becoming "moderately severe" and could get worse, according to a report from The New York Times.

The report from the Times comes on the heels of the CDC's most recent weekly flu update issued Jan. 5, which reported widespread flu activity in 46 states for the week ending Dec. 30 (week 52 of flu season). In week 52 of the 2016-17 flu season, the CDC reported widespread flu activity in 12 states. Additionally, the percentage of outpatient visits for influenza-like illness was 5.8 percent for the week ending Dec. 30, which sits above the national baseline of 2.2 percent.

"These indicators are similar to what was seen at the peak of the 2014-15 season, which was the most severe season in recent years," said the CDC in its summary of last week's flu update.

Here are three reasons this year's flu season could get worse.

1. Weather: The flu virus is essentially designed to move "from person to person when the air is cold and dry," according to a recent report in Popular Science. Toward the end of December through the beginning of January, parts of the central and eastern United States experienced record-setting cold temperatures, according to data from the Southeast Regional Climate Center. If the U.S. sees comparable cold spells in the coming months, it could help facilitate more widespread viral activity.

2. H3N2: About 80 percent of the flu cases identified this flu season have been H3N2 — a strain of seasonal influenza A that tends to be more deadly in young children and the elderly than its influenza A H1N1 counterpart and influenza B strains that tend to pop up with more frequency later in the flu season.

"H3N2 is a bad virus," Daniel Jernigan, MD, director of the influenza division of the CDC, told the Times. "We hate H3N2."

However, Dr. Jernigan said he still suspects fewer deaths will be reported this flu season than in the "moderately severe" 2014-15 flu season, as the current influenza hospitalization rate is only half that reported at this point in the 2014-15 season.

3. Imperfect vaccine: While the H3N2 component of the flu vaccine was reportedly only 10 percent effective in Australia, where the strain resulted in many hospitalizations and deaths in 2017, Dr. Jernigan and Anthony Fauci, MD, director of the National Institute for Allergy and Infectious Disease, told the Times they expect the H3N2 component to be about 30 percent effective in the U.S. This is partly due to the fact that more healthy people in America get the flu shot, as Australian health officials only recommend the vaccine for healthcare workers and those deemed to be at high risk.

The issue with the vaccine was not caused by a genetic shift in the flu, but rather a problem with how the vaccine was made. According to the Times, it was grown in eggs, where "it picked up mutations foreign to human flu." Dr. Fauci is one of the authors of an article published Jan. 4 in The New England Journal of Medicine advocating for the creation of a universal flu vaccine that does not rely on eggs.

Despite the vaccine's imperfection, health officials staunchly advocate for the public to get vaccinated.

"It's far from a perfect vaccine, but we can still do a lot of good with a pretty good one," William Schaffner, MD, head of preventive medicine at Vanderbilt University's medical school in Nashville, Tenn., told the Times.

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