You may have noticed a rash of provocative headlines this week suggesting that mouthwash can "inactivate" coronaviruses and help curb their spread. While the news is based on a new study from researchers at the Penn State College of Medicine, it's important to note that the study focused on a coronavirus that causes common colds -- not the one that causes COVID-19. "Not only did the study not investigate this deadly new virus, but it also did not test whether mouthwash affects how viruses spread from person to person," adds Katherine J. Wu via The New York Times. From the report: "I don't have a problem with using Listerine," said Angela Rasmussen, a virologist at Columbia University. "But it's not an antiviral." The study, which was published last month in the Journal of Medical Virology, looked only at a coronavirus called 229E that causes common colds -- not the new coronavirus, which goes by the formal name of SARS-CoV-2, and causes far more serious disease. Researchers can study SARS-CoV-2 only in high-security labs after undergoing rigorous training. The two viruses are in the same family, and, in broad strokes, look anatomically similar, which can make 229E a good proxy for SARS-CoV-2 in certain experiments. But the two viruses shouldn't be thought of as interchangeable, Dr. Rasmussen said.
The researchers tested the virus-destroying effects of several products, including a watered-down mixture of Johnson's baby shampoo -- which is sometimes used to flush out the inside of the nose -- and mouthwashes made by Listerine, Crest, Orajel, Equate and C.V.S. They flooded 229E coronaviruses, which had been grown in human liver cells in the lab, with these chemicals for 30 seconds, 1 minute or 2 minutes -- longer than the typical swig or spritz into a nose or mouth. Around 90 to 99 percent of the viruses could no longer infect cells after this exposure, the study found.
But because the study didn't recruit any human volunteers to gargle the products in question, the findings have limited value for the real world, other experts said. The human mouth, full of nooks and crannies and a slurry of chemicals secreted by a diverse cadre of cells, is far more complicated than the inside of a laboratory dish. Nothing should be considered conclusive "unless human studies are performed," said Dr. Maricar Malinis, an infectious disease expert at Yale University. [...] 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.
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