Wildfire smoke may help virus spread, mouthwash helps curb it

By Nancy Lapid

(Reuters) – The following is a roundup of some of the latest scientific studies on the novel coronavirus and efforts to find treatments and vaccines for COVID-19, the illness caused by the virus.

Wildfire smoke likely helped to spread COVID-19

Large wildfires may be linked to increases in COVID-19 cases and deaths in the San Francisco area, according to a paper in the European Review for Medical and Pharmacological Sciences. Researchers found that between March and September, increases in smoke particles, other wildfire pollutants and carbon monoxide levels corresponded to increases in daily COVID-19 diagnoses and total COVID-19 deaths. While correlation does not necessarily mean causality, coauthor Sultan Ayoub Meo of King Saud University in Saudi Arabia said air pollution provides a means for viruses to move around the environment. These tiny pollution particles, along with the microorganisms they carry, “can easily be inhaled deep into the lungs and cause infections,” Meo said. “Carbon monoxide is a highly toxic gas which can damage our lungs, resulting as a triggering factor for an increase in COVID-19 cases and deaths in the wildfire region,” he told Reuters. (

Antiviral mouthwash could help curb coronavirus transmission

Mouthwashes with antiviral ingredients could help decrease COVID-19 transmission by reducing viral loads in the mouths of infected patients when they cough, sneeze or speak, according to a paper in the Journal of Dental Research published on Thursday. Studies have found that rinses containing cetylpyridinium chloride or povidone-iodine can reduce the oral coronavirus load; other promising compounds include hydrogen peroxide, chlorhexidine, cyclodextrin, Citrox, and certain essential oils. Coauthor Dr. Florence Carrouel of University Claude Bernard Lyon in France told Reuters everyone should be using these mouthwashes because people can be infected and not realize it. While more studies are needed to determine appropriate regimens, she suggests using three doses of antiviral mouthwash the day before a meeting, and one dose the morning of the event. COVID-19 patients should be using mouthwash regularly for seven to 10 days. (

Common-cold antibodies may hijack body’s COVID-19 response

A phenomenon called “antigenic sin” may explain why some COVID-19 patients become critically ill, researchers say. Because the new virus shares some features with coronaviruses that cause common colds, the body’s immune response can include antibodies that previously learned to recognize and attack those older viruses. This can in turn detract from the body’s ability to fight COVID-19, because the common cold antibodies do not reliably attack the new virus. In severely ill COVID-19 patients, the immune response directed at other coronaviruses is higher than in mildly ill patients, researchers reported on medRxiv ahead of peer review. This situation – when the body reacts to a new invader based on its “memory” of previous invaders – has been seen before and is called “original antigenic sin.” New vaccines must be able to prompt an immune response against this new virus, not merely boost immune responses toward common cold viruses, said coauthor Gijsbert van Nierop of Erasmus Medical

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Mouthwash and covid: What the new research really means

“It’s an exciting avenue, especially as we face many increasing challenges with access to vaccines and different therapeutics,” said Nicholas Rowan, an ear, nose and throat surgeon and assistant professor at Johns Hopkins Medicine. “However, I think it’s also important to realize that it’s not an instant solution and it’s something that we need to do our due diligence on.”

Here’s what those studies on mouthwash and coronaviruses actually mean — and why scientists say we should view their results with cautious enthusiasm.

Studying the effects of mouthwash and other oral antiseptic rinses on infectious viruses is not a novel idea. But amid the ongoing pandemic, fueled by a contagious pathogen often found in people’s mouths and noses, there is now “great interest in this area,” said Yvonne Kapila, periodontology chair in the Department of Orofacial Sciences at the University of California at San Francisco.

Over the past several months, researchers in the United States and abroad have examined mouthwashes, oral antiseptics and nasal rinses in controlled laboratory settings to see whether they can effectively inactivate the new coronavirus and other viruses within the same family.

A team in Germany found that when several products, including Listerine, were applied to strains of the novel coronavirus for 30 seconds, they “significantly reduced viral infectivity to undetectable levels,” according to a study published in July in the Journal of Infectious Diseases.

Researchers at Pennsylvania State University College of Medicine recently released similar findings, reporting that Listerine and Listerine-like products could inactivate more than 99.9 percent of a virus similar to the one that causes covid-19 with just 30 seconds of exposure. In a study published in the Journal of Medical Virology, the scientists wrote that their results suggest mouthwash could potentially decrease the risk of transmission of the novel coronavirus and “provide an additional level of protection.”

“The data suggests that if you have virus in your mouth, it would kill it” and could reduce your ability to spread it to others, said Craig Meyers, the study’s lead researcher and a professor in the university’s departments of microbiology and immunology and obstetrics and gynecology.

A 1 percent solution of baby shampoo, which is often used by head and neck doctors to rinse sinuses, was also shown to effectively inactivate the virus tested after two minutes of exposure, according to the study.

Meyers noted that the focus of the research was to find a way to lower transmission in situations where masking and being more than six feet apart might not be an option, for instance, during dental procedures.

But the findings do not necessarily mean using mouthwash or nasal rinses will protect you from getting infected, Rowan said.

“I do not think that they’re a good protective measure,” he said. “We’re looking at how it actually works on the virus itself rather than what it does to the body. I think those are two separate questions. . . . The question that we’ve asked so far is does this medication, does this

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Can mouthwash protect against coronavirus? Experts discuss results of viral study

Before you stockpile Listerine, take the findings of a recent study with a grain of salt — at least until the results are replicated in a human clinical trial, several experts told Fox News. 

A new study conducted by researchers with Penn State College of Medicine and recently published in the Journal of Medical Virology found that mouthwash and oral rinses can “inactivate” human coronaviruses, with the study authors hypothesizing that these common dental hygiene products could possibly help to slow the spread of the novel coronavirus itself. 

“We were clear that this is not a cure … but that the data suggest a strong potential to lower transmission," lead study author Craig Meyers, a distinguished professor of microbiology and immunology and obstetrics and gynecology, told Fox News. (iStock)

“We were clear that this is not a cure … but that the data suggest a strong potential to lower transmission,” lead study author Craig Meyers, a distinguished professor of microbiology and immunology and obstetrics and gynecology, told Fox News. (iStock)

Though the study’s authors didn’t test the new coronavirus, SARS-CoV-2, when conducting their research, the human coronavirus they did analyze  — a common cold-causing strain known as 229e — is “genetically similar”  to SARS-CoV-2, leading the study authors to argue the results could be comparable. 

For the study, researchers tested various oral and nasopharyngeal rinses — which included a 1% solution of baby shampoo, a neti pot, peroxide sore-mouth cleansers, and mouthwashes, namely Listerine Antiseptic, Orajel Antiseptic Rinse, and Crest Pro‐Health, among others — to determine how well they inactivated the 229e strain. 


Human volunteers were not used; the 229e coronaviruses were grown in human liver cells in the lab before being immersed in the various solutions for 30 seconds, one minute and two minutes. 

The baby shampoo solution, “which is often used by head and neck doctors to rinse the sinuses,” the researchers noted in a news release regarding the findings, was particularly effective; the solution inactivated “greater than 99.9% of human coronavirus after a two-minute contact time,” they said. 

The mouthwash and oral rinses tested were also effective, they found: “Many inactivated greater than 99.9% of virus after only 30 seconds of contact time and some inactivated 99.99% of the virus after 30 seconds.” 

Lead study author Craig Meyers, a distinguished professor of microbiology and immunology and obstetrics and gynecology, said the results show the amount of virus (viral load) in an infected person’s mouth could be reduced by using these common over-the-counter products, possibly helping to reduce the spread of the novel virus in specific instances, like when caring for a COVID patient or visiting the dentist. 


But some experts who were not involved in the study warned the findings shouldn’t be over-interpreted, emphasizing the need for clinical trials to show similar results in humans (in fact, several have already begun recruiting.) 

Additionally, while mouthwash could theoretically reduce the viral load in the oral cavity and throat for a short period of time, the dental product cannot stop the virus from replicating in cells within the body, noted many of the experts who spoke to Fox News. 

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No, Mouthwash Will Not Save You From the Coronavirus

Dr. Meyers said he hoped his team would undertake such studies soon, and noted that a handful of clinical trials had already begun investigating these questions.

The study’s findings aren’t necessarily surprising, or even unprecedented. Other researchers have conducted similar experiments, including one that looked at the effects of mouthwash on the new coronavirus, with comparable results. And since the early days of the pandemic, scientists have stressed the effectiveness of hand-washing and disinfection with soap, alcohol and other similar chemicals that can bust through the new coronavirus’s fragile outer layer, or envelope. (Not all mouthwashes or nasal rinses contain such potent ingredients, however.)

Dr. Valerie Fitzhugh, a pathologist at Rutgers University, pointed to a study from the 1990s, in which researchers in Texas inactivated a strain of flu virus by swirling it in Listerine for 30 seconds. But that study “was never shown to be clinically relevant,” she said.

Even if people did a very thorough job coating the inside of their mouths or noses with a coronavirus-killing chemical, a substantial amount of the virus would still remain in the body. The new coronavirus infiltrates not only the mouth and nose, but also the deep throat and lungs, where mouthwash and nasal washes hopefully never enter.

Viruses that have already hidden away inside cells will also be shielded from the fast-acting chemicals found in these products. “It’s not like your cells get infected and then they secrete a bunch of virus and they’re done,” Dr. Rasmussen said. “Infected cells are constantly making more virus. It’s a timing issue.”

Relying on mouthwash or a nasal rinse to rid the body of infectious virus would be about as futile as trimming the top of a cluster of weeds, paying the roots little mind, and expecting the garden pests to disappear.

Dr. Meyers acknowledged this limitation. After a quick swizzle of mouthwash, “How long do you have? I don’t know,” he said. “All we’re saying right now is, this could add an extra layer of protection,” he explained, on top of proven protective measures like mask-wearing and physical distancing.

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