Photograph by Justin Sullivan, Getty
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A woman receives a free flu shot from a Walgreens employee during a free flu shot clinic at Allen Temple Baptist Church on December 19, 2014 in Oakland, California.

Photograph by Justin Sullivan, Getty

What Makes This Flu Season So Bad

A dangerous strain paired with less effective vaccines has created a dangerous recipe for illness.

A person, commuting to work on a packed bus, coughs. If they're infected with the flu virus, these symptoms could be a recipe for disaster.

Imperceptible to the human eye, the flu virus is one of the most pervasive and persistent on the planet. It mates and spreads in the air. One strain is capable of circumventing the globe in a matter of months.

A recently published Centers for Disease Control and Prevention (CDC) report confirmed what hospitals around the U.S. already know—2017/2018 is a bad year for the flu.

Out of every 100,000 hospitalizations in the U.S., 22.7 were for the flu in the first week in January. According to the CDC, the number had doubled from the week before. During the severe flu season that ended in 2015, rates of hospitalizations reached 29.9 for every 100,000.

During a recent January 12 call with reporters, CDC doctor and director of the influenza division Dan Jernigan noted that the flu was widespread across the continental U.S. In the U.K., flu cases have skyrocketed. It follows a similar pattern seen in Australia during their flu season.

National Geographic spoke with three experts about why this year's flu season is unique. Below, we share their responses.

How Flu Viruses Attack

How Bad Is This Year's Flu?

The winter season that began in 2017 and will end in 2018 "unquestionably falls into a bad year," says Anthony Fauci, director of the National Institutes of Health National Institute of Allergy and Infectious Disease.

"Flu seasons every year are bad so there's never a mild flu season," Jernigan noted on the call.

Lone Simonsen, an epidemiologist at George Washington University, is taking a bit more measured view. "It looks right now like a moderate season, but it takes a few weeks to make the final verdict," says Simonsen.

The CDC measures rates of hospitalizations and illness by weeks, and the last time the flu was historically bad was during the beginning weeks of 2015. However, it’s important to remember that flu levels exceed the CDC's threshold to be considered an epidemic almost every year.

This year's flu rates have yet to reach the levels seen three years ago, but flu season is currently at its peak and current trends suggest they could get worse.

Why Is it So Bad?

This year's unfolding flu season can be explained threefold, says Fauci.

First, he says, is the nature of the most dominant flu strain infecting people—H3N2. Flu viruses mutate every year, and it's common to see several strains of flu during the same season. A similar strain called H1N1 was responsible for the 1918 flu pandemic, and the 2009 "swine flu" outbreak.

"H3N2 is historically the bad actor among influenzas," he says. "It's also associated with complications."

H3N2 is also the dominant strain in the U.K. and was the dominant flu strain in Australia.

The second reason H3N2 has been so pervasive, says Fauci, is people have less exposure to it. When the same flu strain strikes repeatedly, people and thus regions tend to build up immunity.

The third reason this year's flu has been so bad is complications with the vaccine. Most influenza vaccines are grown in chicken eggs, and when this year's vaccine was being incubated, the virus mutated while it was growing and became less effective.

Scientists think it may only be about 30 percent effective against H3N2. In Australia, the vaccine was only 10 percent effective.

How Is it Treated?

At best, says Fauci, flu vaccines are only ever about 60 percent effective. While that makes it at least 60 percent more effective than not getting a vaccine at all, it still means the rapidly mutating virus has a fighting chance.

Every year, the World Health Organization (WHO) meets to determine what specific flu strains should receive vaccines in the northern hemisphere. H3N2 was one of several identified as a threat.

The "Holy Grail" or Universal Vaccine

There are four different types of influenza virus, three of which infect people. Of those three, influenza A and B are the most common and each of those subsets develops different strains. H1N1 and H3N2, for example, are strains of influenza A, and they adapt by constantly changing their surface proteins.

"The holy grail is to target a piece of the virus by antibody or t cell," says Tom Evans, the CEO of a company called Vaccitech that is working on a universal vaccine they hope can be used to treat all strains of influenza A.

"The body prefers to make a response to the part of the virus that changes," says Fauci, who is also overseeing NIH groups working on universal vaccines. "It's our job to present to the body this molecule that makes a specific response against the part that doesn't change."

Through clinical trials, Evans hopes to answer his current hypothesis within two years but says an additional five years after that will be needed to improve upon the research group's findings. Fauci, too says that some headway has been made, but a universal vaccine is still at least several years in the works.

What to Do Now

Available flu vaccines should still be taken, says Simonsen, though she adds it's important to remember they take a week or two to become effective. Not only do they increase the odds of not getting the flu, she says, but they also prevent spreading the virus to at-risk groups like the young, elderly, or those with serious medical conditions. The flu is rarely lethal in healthy individuals.

Once infected, flu patients can also take antivirals to help kill off the virus more quickly.