Are betadine mouthwashes really effective against COVID-19?
In vitro (test tubes/culture plates) studies do show that providone iodine does kill viruses similar to SARS-CoV-2 after sufficient exposure (just as bleach and ethyl/isopropyl alcohol do.)
The answer in vivo (in humans or animals) is unknown. (N.B.: That's, unknown, as in, you should probably wait for more studies before (potentially serioulsy) harming yourself. Remember bleach, ethyl alcohol at or above 70% -140 proof - and certain industrial disinfectants do the same, which does not mean they should be used on human tissue. Most available PVP-I solutions available are toxic, even if diluted.)
The first study listed found that in vitro,
PVP-I gargle/mouthwash diluted 1:30 (equivalent to a concentration of 0.23% PVP-I) showed effective bactericidal activity against Klebsiella pneumoniae and Streptococcus pneumoniae and rapidly inactivated SARS-CoV, MERS-CoV, influenza virus A (H1N1) and rotavirus after 15 s of exposure.
It is only assumed that because it is effective against SARS-CoV, it is also effective against SARS-CoV-2.
It should be noted that not all providone-iodine solutions are created equally; the gargle preparation used in Japan cannot be obtained in the US and many other parts of the world, and the solutions used in the US are toxic at the same concentrations.
The second paper listed also notes
The utility and excellent safety profile of both topical nasal and oral solutions of PVP-I has long been recognized, especially at dilute concentrations (e.g. 0.001%). A detailed review of its virucidal activity against a wide range of common viruses, including SARS-CoV and MERS-CoV coronaviruses, is beyond the scope of this article.
The next line is
As a word of caution, in vitro studies using 10% and 5% PVP-I have demonstrated cilotoxicity on human respiratory cells.
They go on to propose use of PVP-I on patients known to or suspected of having Covid-19 on whom high-risk procedures are being performed (head/neck surgery) and on healthcare providers pre- and post- exposure to these patients (Apply nasal and oral PVP-I prior to and after patient contact (with repeated contact, apply every 2–3 h, up to 4×/day) in healthcare providers that who lack adequate PPE (e.g. N95, PAPR).
They go on to conclude, in part,
It is important to acknowledge that there is a potential risk in that prophylactic treatment of healthcare providers could increase susceptibility to SARS-CoV-2 infection by affecting mucociliary function or local immunity.
One study seems stalled (cause unknown, recruitment issues?)
while another tested (in vitro) a very specific kind of PVP-I (gel-forming) in very limited circumstances.
The last paper is detailed and thorough (though please note the word potential in the title), and you can skip directly to the PVP-I section, where they state
[the Japanese] mouthwash is not available in the United Kingdom, although may still be purchased in Germany and other countries. As a 1% solution, PVP-I is available in Hong Kong, Korea, Singapore, Malaysia, Philippines, and Taiwan.
In Vitro Bactericidal and Virucidal Efficacy of Povidone-Iodine Gargle/Mouthwash Against Respiratory and Oral Tract Pathogens
Consideration of povidone-iodine as a public health intervention for COVID-19: Utilization as “Personal Protective Equipment” for frontline providers exposed in high-risk head and neck and skull base oncology care
COVID-19: Povidone-Iodine Intranasal Prophylaxis in Front-line Healthcare Personnel and Inpatients (PIIPPI)
In-Vivo Toxicity Studies and In-Vitro Inactivation of SARS-CoV-2 by Povidone-iodine In-situ Gel Forming Formulations
Potential Role of Oral Rinses Targeting the Viral Lipid Envelope in SARS-CoV-2 Infection
Edited to add: In case there is confusion, I stated that the answer is unknown, and that most PVP-I solutions available are toxic in most countries. I am not an advocate of its use any more than 70% ethyl alcohol or bleach!
I answered this question because it's important to engage with people reaching out for some answers in this pandemic, and because harmful advice is rife now (Even national leaders are making them, and they are surrounded by experts.) And to show that their concerns weren't unshared by some physicians. And that, like Barry Marshall's discovery, sometimes it's the most "ridiculous", "preposterous", and "idiotic" things that turn out to be true in medicine. But Barry Marshall paid a high price to prove his theory, both physically and emotionally, though winning the Nobel Prize was a very nice apology and recognition of the millions upon millions of people he saved from the barbaric approach to chronic ulcer treatment and stomach cancers before his discovery.