The World Health Organization has issued a report that transforms how the world understands respiratory infections like covid-19, influenza, and measles.

Motivated by grave missteps in the pandemic, the WHO convened about 50 experts in virology, epidemiology, aerosol science, and bioengineering, among other specialties, who spent two years poring through the evidence on how airborne viruses and bacteria spread.

However, the WHO report stops short of prescribing actions that governments, hospitals, and the public should take in response. It remains to be seen how the Centers for Disease Control and Prevention will act on this information in its own guidance for infection control in health care settings.

The WHO concluded that airborne transmission occurs as sick people exhale pathogens that remain suspended in the air, contained in tiny particles of saliva and mucus that are inhaled by others.

While it may seem obvious, and some researchers have pushed for this acknowledgment for more than a decade, an alternative dogma persisted — which kept health authorities from saying that covid was airborne for many months into the pandemic.

Specifically, they relied on a traditional notion that respiratory viruses spread mainly through droplets spewed out of an infected person’s nose or mouth. These droplets infect others by landing directly in their mouth, nose, or eyes — or they get carried into these orifices on droplet-contaminated fingers. Although these routes of transmission still happen, particularly among young children, experts have concluded that many respiratory infections spread as people simply breathe in virus-laden air.

“This is a complete U-turn,” said Julian Tang, a clinical virologist at the University of Leicester in the United Kingdom, who advised the WHO on the report. He also helped the agency create an online tool to assess the risk of airborne transmission indoors.

Peg Seminario, an occupational health and safety specialist in Bethesda, Maryland, welcomed the shift after years of resistance from health authorities. “The dogma that droplets are a major mode of transmission is the ‘flat Earth’ position now,” she said. “Hurray! We are finally recognizing that the world is round.”

The change puts fresh emphasis on the need to improve ventilation indoors and stockpile quality face masks before the next airborne disease explodes. Far from a remote possibility, measles is on the rise this year and the H5N1 bird flu is spreading among cattle in several states. Scientists worry that as the H5N1 virus spends more time in mammals, it could evolve to more easily infect people and spread among them through the air.

Traditional beliefs on droplet transmission help explain why the WHO and the CDC focused so acutely on hand-washing and surface-cleaning at the beginning of the pandemic. Such advice overwhelmed recommendations for N95 masks that filter out most virus-laden particles suspended in the air. Employers denied many health care workers access to N95s, insisting that only those routinely working within feet of covid patients needed them. More than 3,600 health care workers died in the first year of the pandemic, many due to a lack of protection.

However, a committee advising the CDC appears poised to brush aside the updated science when it comes to its pending guidance on health care facilities.

Lisa Brosseau, an aerosol expert and a consultant at the Center for Infectious Disease Research and Policy in Minnesota, warns of a repeat of 2020 if that happens.

“The rubber hits the road when you make decisions on how to protect people,” Brosseau said. “Aerosol scientists may see this report as a big win because they think everything will now follow from the science. But that’s not how this works and there are still major barriers.”

Money is one. If a respiratory disease spreads through inhalation, it means that people can lower their risk of infection indoors through sometimes costly methods to clean the air, such as mechanical ventilation and using air purifiers, and wearing an N95 mask. The CDC has so far been reluctant to press for such measures, as it updates foundational guidelines on curbing airborne infections in hospitals, nursing homes, prisons, and other facilities that provide health care. This year, a committee advising the CDC released a draft guidance that differs significantly from the WHO report.

Whereas the WHO report doesn’t characterize airborne viruses and bacteria as traveling short distances or long, the CDC draft maintains those traditional categories. It prescribes looser-fitting surgical masks rather than N95s for pathogens that “spread predominantly over short distances.” Surgical masks block far fewer airborne virus particles than N95s, which cost roughly 10 times as much.

Researchers and health care workers have been outraged about the committee’s draft, filing letters and petitions to the CDC. They say it gets the science wrong and endangers health. “A separation between short- and long-range distance is totally artificial,” Tang said.

Airborne viruses travel much like cigarette smoke, he explained. The scent will be strongest beside a smoker, but those farther away will inhale more and more smoke if they remain in the room, especially when there’s no ventilation.

Likewise, people open windows when they burn toast so that smoke dissipates before filling the kitchen and setting off an alarm. “You think viruses stop after 3 feet and drop to the ground?” Tang said of the classical notion of distance. “That is absurd.”

The CDC’s advisory committee is comprised primarily of infection control researchers at large hospital systems, while the WHO consulted a diverse group of scientists looking at many different types of studies. For example, one analysis examined the puff clouds expelled by singers, and musicians playing clarinets, French horns, saxophones, and trumpets. Another reviewed 16 investigations into covid outbreaks at restaurants, a gym, a food processing factory, and other venues, finding that insufficient ventilation probably made them worse than they would otherwise be.

In response to the outcry, the CDC returned the draft to its committee for review, asking it to reconsider its advice. Meetings from an expanded working group have since been held privately. But the National Nurses United union obtained notes of the conversations through a public records request to the agency. The records suggest a push for more lax protection. “It may be difficult as far as compliance is concerned to not have surgical masks as an option,” said one unidentified member, according to notes from the committee’s March 14 discussion. Another warned that “supply and compliance would be difficult.”

The nurses’ union, far from echoing such concerns, wrote on its website, “The Work Group has prioritized employer costs and profits (often under the umbrella of ‘feasibility’ and ‘flexibility’) over robust protections.” Jane Thomason, the union’s lead industrial hygienist, said the meeting records suggest the CDC group is working backward, molding its definitions of airborne transmission to fit the outcome it prefers.

Tang expects resistance to the WHO report. “Infection control people who have built their careers on this will object,” he said. “It takes a long time to change people’s way of thinking.”

The CDC declined to comment on how the WHO’s shift might influence its final policies on infection control in health facilities, which might not be completed this year. Creating policies to protect people from inhaling airborne viruses is complicated by the number of factors that influence how they spread indoors, such as ventilation, temperature, and the size of the space.

Adding to the complexity, policymakers must weigh the toll of various ailments, ranging from covid to colds to tuberculosis, against the burden of protection. And tolls often depend on context, such as whether an outbreak happens in a school or a cancer ward.

“What is the level of mortality that people will accept without precautions?” Tang said. “That’s another question.”

KFF Health News is a national newsroom that produces in-depth journalism about health issues and is one of the core operating programs at KFF—an independent source of health policy research, polling, and journalism. Learn more about KFF.

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In 2013, the FDA approved an implantable device to treat leaky heart valves. Among its inventors was Mehmet Oz, the former television personality and former U.S. Senate candidate widely known as “Dr. Oz.”

In online videos, Oz has called the process that brought the MitraClip device to market an example of American medicine firing “on all cylinders,” and he has compared it to “landing a man on the moon.”

MitraClip was designed to spare patients from open-heart surgery by snaking hardware into the heart through a major vein. Its manufacturer, Abbott, said it offered new hope for people severely ill with a condition called mitral regurgitation and too frail to undergo surgery.

“It changed the face of cardiac medicine,” Oz said in a video.

But since MitraClip won FDA approval, versions of the device have been the subject of thousands of reports to the agency about malfunctions or patient injuries, as well as more than 1,100 reports of patient deaths, FDA records show. Products in the MitraClip line have been the subject of three recalls. A former employee has alleged in a federal lawsuit that Abbott promoted the device through illegal inducements to doctors and hospitals. The case is pending, and Abbott has denied illegally marketing the device.

The MitraClip story is, in many ways, a cautionary tale about the science, business, and regulation of medical devices.

Manufacturer-sponsored research on the device has long been questioned. In 2013, an outside adviser to the FDA compared some of the data marshaled in support of its approval to “poop.”

The FDA expanded its approval of MitraClip to a wider set of patients in 2019, based on a clinical trial in which Abbott was deeply involved and despite conflicting findings from another study.

In the three recalls, the first of which warned of potentially deadly consequences, neither the manufacturer nor the FDA withdrew inventory from the market. The company told doctors it was OK for them to continue using the recalled products.

In response to questions for this article, both Abbott and the FDA described MitraClip as safe and effective.

“With MitraClip, we’re addressing the needs of people with MR who often have no other options,” Abbott spokesperson Brent Tippen said. “Patients suffering from mitral regurgitation have severely limited quality of life. MitraClip can significantly improve survival, freedom for hospitalization and quality of life via a minimally invasive, now common procedure.”

An FDA spokesperson, Audra Harrison, said patient safety “is the FDA’s highest priority and at the forefront of our work in medical device regulation.”

She said reports to the FDA about malfunctions, injuries, and deaths that the device may have caused or contributed to are “consistent” with study results the FDA reviewed for its 2013 and 2019 approvals.

In other words: They were expected.

Inspiration in Italy

When a person has mitral regurgitation, blood flows backward through the mitral valve. Severe cases can lead to heart failure.

With MitraClip, flaps of the valve — known as “leaflets” — are clipped together at one or more points to achieve a tighter seal when they close. The clips are deployed via a catheter threaded through a major vein, typically from an incision in the groin. The procedure offers an alternative to connecting the patient to a heart-lung machine and repairing or replacing the mitral valve in open-heart surgery.

Oz has said in online videos that he got the idea after hearing a doctor describe a surgical technique for the mitral valve at a conference in Italy. “And on the way home that night, on a plane heading back to Columbia University, where I was on the faculty, I wrote the patent,” he told KFF Health News.

A patent obtained by Columbia in 2001, one of several associated with MitraClip, lists Oz first among the inventors.

But a Silicon Valley-based startup, Evalve, would develop the device. Evalve was later acquired by Abbott for about $400 million.

“I think the engineers and people at Evalve always cringe a little bit when they see Mehmet taking a lot of, you know, basically claiming responsibility for what was a really extraordinary team effort, and he was a small to almost no player in that team,” one of the company’s founders, cardiologist Fred St. Goar, told KFF Health News.

Oz did not respond to a request for comment on that statement.

As of 2019, the MitraClip device cost $30,000 per procedure, according to an article in a medical journal. According to the Abbott website, more than 200,000 people around the world have been treated with MitraClip.

Oz filed a financial disclosure during his unsuccessful run for the U.S. Senate in 2022 that showed him receiving hundreds of thousands of dollars in annual MitraClip royalties.

Abbott recently received FDA approval for TriClip, a variation of the MitraClip system for the heart’s tricuspid valve.

Endorsed ‘With Trepidation’

Before the FDA said yes to MitraClip in 2013, agency staffers pushed back.

Abbott had originally wanted the device approved for “patients with significant mitral regurgitation,” a relatively broad term. After the FDA objected, the company narrowed its proposal to patients at too-high risk for open-heart surgery.

Even then, in an analysis, the FDA identified “fundamental” flaws in Abbott’s data.

One example: The data compared MitraClip patients with patients who underwent open-heart surgery for valve repair — but the comparison might have been biased by differences in the expertise of doctors treating the two groups, the FDA analysis said. While MitraClip was implanted by a highly select, experienced group of interventional cardiologists, many of the doctors doing the open-heart surgeries had performed only a “very low volume” of such operations.

FDA “approval is not appropriate at this time as major questions of safety and effectiveness, as well as the overall benefit-risk profile for this device, remain unanswered,” the FDA said in a review prepared for a March 2013 meeting of a committee of outside advisers to the agency.

Some committee members expressed misgivings. “If your right shoe goes into horse poop and your left shoe goes into dog poop, it’s still poop,” cardiothoracic surgeon Craig Selzman said, according to a transcript.

The committee voted 5-4 against MitraClip on the question of whether it proved effective. But members voted 8-0 that they considered the device safe and 5-3 that the benefits of the device outweighed its risks.

Selzman voted yes on the last question “with trepidation,” he said at the time.

In October 2013, the FDA approved the MitraClip Clip Delivery System for a narrower group of patients: those with a particular type of mitral regurgitation who were considered a surgery risk.

“The reality is, there is no perfect procedure,” said Jason Rogers, an interventional cardiologist and University of California-Davis professor who is an Abbott consultant. The company referred KFF Health News to Rogers as an authority on MitraClip. He called MitraClip “extremely safe” and said some patients treated with it are “on death’s door to begin with.”

“At least you’re trying to do something for them,” he said.

Conflicting Studies

In 2019, the FDA expanded its approval of MitraClip to a wider set of patients.

The agency based that decision on a clinical trial in the United States and Canada that Abbott not only sponsored but also helped design and manage. It participated in site selection and data analysis, according to a September 2018 New England Journal of Medicine paper reporting the trial results. Some of the authors received consulting fees from Abbott, the paper disclosed.

A separate study in France reached a different conclusion. It found that, for some patients who fit the expanded profile, the device did not significantly reduce deaths or hospitalizations for heart failure over a year.

The French study, which appeared in the New England Journal of Medicine in August 2018, was funded by the government of France and Abbott. As with the North American study, some of the researchers disclosed they had received money from Abbott. However, the write-up in the journal said Abbott played no role in the design of the French trial, the selection of sites, or in data analysis.

Gregg Stone, one of the leaders of the North American study, said there were differences between patients enrolled in the two studies and how they were medicated. In addition, outcomes were better in the North American study in part because doctors in the U.S. and Canada had more MitraClip experience than their counterparts in France, Stone said.

Stone, a clinical trial specialist with a background in interventional cardiology, acknowledged skepticism toward studies sponsored by manufacturers.

“There are some people who say, ‘Oh, well, you know, these results may have been manipulated,’” he said. “But I can guarantee you that’s not the truth.”

‘Nationwide Scheme’

A former Abbott employee alleges in a lawsuit that after MitraClip won approval, the company promoted the device to doctors and hospitals using inducements such as free marketing support, the chance to participate in Abbott clinical trials, and payments for participating in “sham speaker programs.”

The former employee alleges that she was instructed to tell referring physicians that if they observed mitral regurgitation in their patients to “just send it” for a MitraClip procedure because “everything can be clipped.” She also alleges that, using a script, she was told to promote the device to hospital administrators based on financial advantages such as “growth opportunities through profitable procedures, ancillary tests, and referral streams.”

The inducements were part of a “nationwide scheme” of illegal kickbacks that defrauded government health insurance programs including Medicare and Medicaid, the lawsuit claims.

The company denied doing anything illegal and said in a court filing that “to help its groundbreaking therapy reach patients, Abbott needed to educate cardiologists and other healthcare providers.”

Those efforts are “not only routine, they are laudable — as physicians cannot use, or refer a patient to another doctor who can use, a device that they do not understand or in some cases even know about,” the company said in the filing.

Under federal law, the person who filed the suit can receive a share of any money the government recoups from Abbott. The suit was filed by a company associated with a former employee in Abbott’s Structural Heart Division, Lisa Knott. An attorney for the company declined to comment and said Knott had no comment.

Reports to the FDA

As doctors started using MitraClip, the FDA began receiving reports about malfunctions and cases in which the product might have caused or contributed to a death or an injury.

According to some reports, clips detached from valve flaps. Flaps became damaged. Procedures were aborted. Mitral leakage worsened. Doctors struggled to control the device. Clips became “entangled in chordae” — cord-like structures also known as heartstrings that connect the valve flaps to the heart muscle. Patients treated with MitraClip underwent corrective operations.

As of March 2024, the FDA had received more than 17,000 reports documenting more than 22,000 “events” involving mitral valve repair devices, FDA data shows. All but about 200 of those reports mention one iteration of MitraClip or another, a KFF Health News review of FDA data found.

Almost all the reports came from Abbott. The FDA requires manufacturers to submit reports when they learn of mishaps potentially related to their devices.

The reports are not proof that devices caused problems, and the same event might be reported multiple times. Other events may go unreported.

Despite the reports’ limitations, the FDA provides an analysis of them for the public on its website.

MitraClip’s risks weren’t a surprise.

Like the rapid-fire fine print in television ads for prescription drugs, the original product label for the device listed more than 60 types of potential complications.

Indeed, during clinical research on the device, about 6% of patients implanted with MitraClip died within 30 days, according to the label. Almost 1 in 4 — 23.6% – were dead within a year.

The FDA spokesperson, Harrison, pointed to a study originally published in 2021 in The Annals of Thoracic Surgery, based on a central registry of mitral valve procedures, that found lower rates of death after MitraClip went on the market.

“These data confirmed that the MitraClip device remains safe and effective in the real-world setting,” Harrison said.

But the study’s authors, several of whom disclosed financial or other connections to Abbott, said data was missing for more than a quarter of patients one year after the procedure.

A major measure of success would be the proportion of MitraClip patients who are alive “with an acceptable quality of life” a year after undergoing the procedure, the study said. Because such information was available for fewer than half of the living patients, “we have omitted those outcomes from this report,” the authors wrote.

If you’ve had an experience with MitraClip or another medical device and would like to tell KFF Health News about it, click here to share your story with us.

KFF Health News audience engagement producer Tarena Lofton contributed to this report.

KFF Health News is a national newsroom that produces in-depth journalism about health issues and is one of the core operating programs at KFF—an independent source of health policy research, polling, and journalism. Learn more about KFF.

Subscribe to KFF Health News’ free Morning Briefing.