The Perfect Storm Behind This Year's Nasty Flu Season

Every winter brings cautionary tales that the flu—just the regular old flu—can kill. And the cautionary tales this year are hard to beat. Twenty-one-year-old Kyler Baughman, for example, a fitness buff who liked to show off his six-pack, recently died a few days after getting a runny nose.

According to the numbers, this year’s flu season is in fact worse than usual. It got started early, and it’s been more severe. Twenty kids have died of the flu since October. And in the week ending January 6, 22.7 out of every 100,000 hospitalizations in the U.S. were for flu—twice the number of the previous week.

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“Flu is everywhere in the U.S. right now,” Dan Jernigan, director of the Center for Disease Control and Prevention’s influenza branch, said during a Friday press briefing. “This is the first year we’ve had the entire continental U.S. be the same same color”—referring to a map of state-by-state estimate of flu activity. That color is brown, meaning the flu is “widespread” everywhere in the U.S. except for Hawaii and the District of Columbia.

Several factors have come together make this year’s flu worse for patients who get sick and for hospitals trying to treat them.

First, the virus. Fears of a bad flu season first began in the early fall, after public health officials noticed a worse-than-average flu season in the southern hemisphere. The dominant circulating strain this year is H3N2, which hits humans harder than other strains. Scientists don’t really know why, but flu seasons where H3N2 have dominated in the past have tended to be worse. STAT reporter Helen Branswell called it the “problem child of seasonal flu.”

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H3N2 (red) makes up the majority of lab-confirmed cases of flu this season. (CDC)

Second, the vaccine. This year’s vaccine was only 10 percent effective against the problematic H3N2 strain in Australia.

Flu experts have the unenviable task of predicting circulating flu strains several months in advance—so that vaccine manufacturers have the time it takes to grow millions of doses in chicken eggs. This year, they got the dominant strain right. But even when flu experts do a decent job with their predictions, the other problem is the chicken eggs. Flu viruses can pick up mutations and evolve as they grow in bird cells, which are not their preferred environment. (After all, they want to infect humans.) So in the end, the flu viruses that end up in vaccines look a little different than the ones circulating out in the world. The H3N2 strain is especially prone to significant egg-induced mutations.

In recent years, researchers have tried to stop relying on chicken eggs. This flu season, for the first time, the H3N2 component of one type of vaccine, Flucelvax, was made in dog cells rather than chicken eggs. However, Flucelvax is more expensive and less widely available; most people who got the vaccine this year likely got the ones grown in chicken eggs. Researchers also are pursuing a universal flu vaccine that works against all strains.

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This does not mean that the flu vaccine this year is useless. It still protects against other strains of flu such as H1N1 and B virus, and it provides at least some immunity to H3N2.

Hospitals are dealing with more flu patients at the same that they’re running out of IV bags—basic equipment that is in distressingly short supply across much of the country these days. IV bags, along with a lot of other medical equipment, are manufactured in Puerto Rico. The blackout after Hurricane Maria massively disrupted manufacturing on the island. The plants making IV bags have reconnected to the power grid, but hospitals are still not getting a reliable supply.

Normally, a hospital can go through hundreds of IV bags a day to replenish fluids for patients and to give drugs like antibiotics and painkillers. Some have resorted to directly injecting drugs into the vein via a procedure called “IV push.”

“If we can’t support patients coming in emergency rooms who have the flu, more people are going to die,” Deborah Pasko, director of medication safety and quality at the American Society of Health System Pharmacists, told the Associated Press. “I see it as a crisis.”

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