Health officials, lawmakers and parents have been raising alarms about vaping for a couple of years, warning that products touted as healthier alternatives for smokers are instead drawing in young people with fun flavors and slick marketing — concerns the Trump administration cited Wednesday while announcing plans to ban most flavored e-cigarettes.

The caution has taken on new urgency in recent weeks as authorities scramble to understand a rash of mysterious vaping-linked illnesses that have put healthy people in the hospital with serious lung diseases. On Tuesday, authorities announced a sixth death connected to e-cigarettes, battery-powered devices that can look like flash drives and pens and that mimic smoking by heating liquids containing substances such as nicotine and marijuana.

How did the concerns start?

E-cigarettes have been sold for more than a decade, but reports of vaping-linked illness started proliferating this year.

An investigation by state health departments in Illinois and Wisconsin traces the first signs of illness among 53 tracked patients to April. The victims — mostly young men with a median age of 19 — overwhelmingly ended up in the hospital, many under intensive care. A third went on respirators.

Patients typically experienced coughing, chest pain or shortness of breath before their health deteriorated to the point that they needed to be hospitalized, according to the Centers for Disease Control and Prevention. Other reported symptoms include nausea, vomiting, diarrhea, fatigue, fever and weight loss.

Many victims have ended up with acute respiratory distress syndrome, a life-threatening condition in which fluid builds up in the lungs and prevents the oxygen people’s bodies need to function from circulating in the bloodstream.

The Washington Post’s Lena Sun chronicled one Utah man’s experience with the disease:

Within days, Alexander Mitchell had gone from being a 20-year-old hiking enthusiast to being kept alive by two machines forcing air into and out of his lungs and oxygenating his blood outside of his body.

“He went from being sick to being on death’s door in literally two days,” recalled his father, Daniel Mitchell, as he struggled to grasp the unthinkable. “The doctor said he was dying. In all honesty, I was preparing to plan a funeral for my child. I wept and wept for this boy.”

... Six weeks after he left the hospital, Mitchell has resumed hiking. But with his lung capacity diminished by 25 percent, he doesn’t go for long or as often as he used to. He also struggles with his short-term memory. Doctors say they’re not sure whether he will fully recover.

The first death to a vaping-related illness was reported Aug. 23 in Illinois. At that time, federal and state officials were investigating almost 200 cases of the baffling sickness in 22 states, according to the CDC.

Last week, Oregon officials announced a second death, saying a middle-aged adult fell seriously ill after vaping with marijuana oil. It was the first casualty linked to a store-bought product. (Authorities have not provided product details for the Illinois death).

Three more deaths were soon disclosed in Indiana, Minnesota, California and now Kansas, where a resident over 50 years old with a history of health problems reportedly fell ill after using an unspecified vaping product.

Officials say they are not sure why the afflictions are just now surfacing.

“We’re all wondering if this is new or just newly recognized,” the CDC’s Dana Meaney-Delman said Friday.

Some argue doctors may have missed previous cases: Susan Walley, chair of the American Academy of Pediatrics tobacco control section, told BuzzFeed News that based on her experience, young people might not recognize their use of common e-cigarette brands such as Juul as “vaping” when pediatricians ask.

But others are skeptical that older cases could have gone under the radar.

“You have a lot of otherwise healthy young people suddenly arriving with fast-developing pneumonia in emergency rooms — that will raise red flags in a hurry,” Sean Callahan, a physician at the University of Utah, told BuzzFeed. “This is new.”

Who is affected?

As of Sept. 11, officials counted 380 confirmed and probable cases of vaping-related illness reported by 36 states and the U.S. Virgin Islands, according to the CDC. The previous case count was higher because it reported possible cases that were still under investigation.

While most of the victims have been young, all those who died were adults, according to authorities. Four were middle-aged or older; the ages of the other have not been specified.

What do we know about the cause of the illnesses?

Officials are still trying to figure out what, exactly, is causing people to fall ill. They think chemicals are to blame.

“The focus of our investigation is narrowing, and that is great news, but we are still faced with complex questions in this outbreak that will take time to answer,” said Ileana Arias, CDC acting deputy director for noninfectious diseases.

The nationwide investigation has found no particular vaping devices or products linked to all cases and is looking into potential contamination or counterfeit, as many victims report buying marijuana on the street rather than from a store.

The Post reported earlier this week that investigators at the Food and Drug Administration found the same vitamin E-derived oil in marijuana products vaped by multiple people sickened around the country. But officials cautioned that they could not yet pin the illnesses on it.

The chemical, vitamin E acetate, was present in almost all of the cannabis samples from victims identified in New York, according to the state’s health department. New York Gov. Andrew M. Cuomo (D) announced on Monday that the state will subpoena three companies selling “thickening agents” used to adjust THC levels in products found on the black market. The thickening agents are “nearly pure” vitamin E acetate, officials say.

And some victims have said they vaped only nicotine products, according to authorities, though doctors also say patients may be hesitant to admit using marijuana.

How are authorities and policymakers responding?

With so many details still unclear, authorities are advising people to put away their e-cigarettes.

New York’s health commissioner, Howard Zucker, warned residents Saturday to stop using vape products until the CDC could determine the cause of the vaping-related illnesses nationwide. He also urged medical marijuana patients to discuss alternatives with their doctors, although no sicknesses have been reported among patients in the state’s medical marijuana program.

The CDC — which is leading inquiries into the illnesses and working with state health departments — has told doctors to ask patients about e-cigarettes when they arrive with symptoms resembling the vaping-linked afflictions and to report the cases to health departments.

Some lawmakers have called for more urgent action from the federal government. Sen. Richard J. Durbin (D-Ill.) on Friday accused the FDA’s acting chief, Norman “Ned” Sharpless, of “sitting on his hands,” tweeting that he would call for the leader’s resignation if he did not “take action in the next 10 days.”

Durbin’s calls for increased e-cigarette regulation come two years after the FDA pushed back its deadline to review the products, which the agency has yet to approve.

A plan for stricter regulations materialized Wednesday, as Health and Human Services Alex Azar announced at a White House gathering with the president and other top officials that the FDA is working to outlaw most flavored vaping products. The policy, which would upend the e-cigarette market, will be finalized in a few weeks and then go into effect 30 days later, he said. The restrictions would be lifted only for products that the FDA approves.

Tobacco-flavored e-cigarettes will not be affected, officials said.

Although the move came amid the growing concern over vaping-linked illness, the Trump administration pointed to a broader rise in teen vaping as its motivation.

How common is vaping?

Vaping has risen dramatically in popularity around the world — from 7 million users in 2011 to 35 million a few years ago — as smoking rates decline.

Tobacco and cigarette company Altria Group estimated nearly 14 million nicotine e-cigarette users in the United States earlier this summer. Another study found last year that more than half of American adult e-cigarette users are under 35 years old, stoking concerns about vaping among young people.

Studies showing vaping’s growing popularity among teens sparked particular worry last year. About 37 percent of 12th-graders reported vaping over the past year in one government-funded U.S. survey released in December — nearly a 10 percentage-point increase from 2017. Past-month nicotine vaping rates among the seniors doubled, and younger students also reported higher use; marijuana vaping rose, too. And a CDC report found last year that e-cigarettes were the most popular product among the nearly 5 million high school and middle school students who used tobacco within a 30-day period.

Why were e-cigarettes controversial before the vaping-linked illness reports?

Mysterious illnesses aside, many have accused e-cigarette manufacturers of exposing young people to addictive nicotine and luring them toward smoking. The National Academies of Science, Engineering and Medicine say they found “substantial evidence” that youths who try vaping are more likely to use conventional cigarettes.

Last fall, then-FDA Commissioner Scott Gottlieb called teenage vaping an “epidemic” as he announced a crackdown on more than 1,300 entities allegedly selling e-cigarettes to minors. He threatened to ban the flavored vaping liquids that have drawn so much scrutiny for their appeal to young people — unless e-cigarette manufacturers such as Juul Labs worked to substantially curb underage use.

The Trump administration’s move to make good on that threat followed growing interest in restricting e-cigarettes at the state and local level. Last week, Michigan became the first state to announce a ban on flavored vaping products. San Francisco — home to Juul Labs — was the first city to ban all e-cigarette sales in June, a year after it outlawed flavored products.

E-cigarette makers have lobbied aggressively against these measures and argue that their products can help smokers quit while giving those addicted to nicotine a safer option than burning tobacco. They say they’re working to address underage vaping and warn that an outright ban could just replace regulated sales with a black market.

The CDC agrees that e-cigarettes can help smokers who substitute them for regular tobacco products, and health professionals believe vaping to be safer than traditional smoking, which kills 8 million people per year, according to the World Health Organization. But given that the FDA has yet to vet vaping products, experts caution that the long-term consequences of using e-cigarettes remain unclear.

Marisa Iati contributed to this report.

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