select search filters
roundups & rapid reactions
before the headlines
Fiona fox's blog

expert reaction to study looking at povidone iodine mouthwash, gargle, and nasal spray and viral load in patients with non-severe COVID-19 symptoms

A study published in JAMA Otolaryngology – Head & Neck Surgery looks at whether nasopharyngeal application of povidone iodine is able to reduce the viral load of patients with non-severe COVID-19 symptoms.


Prof Francois Balloux, Professor of Computational Systems Biology and Director, UCL Genetics Institute, UCL, said:

“I’m afraid that paper contributes very little to our understanding of COVID-19 viral load and transmission.  The sample size of 24 patients is minuscule, there is a massive age difference between treatment and control group, and I can’t even spot a difference by eyeballing the figure.”


Prof Martin Addy, Emeritus Professor of Dentistry, University of Bristol, said:

“Unfortunately this study design would appear to have significant shortcomings and its findings don’t support a clinically significant difference between the two groups.

“The supposed randomised basis of the study has resulted in a dramatic age difference between the two groups – the average age of those treated was 33, while those untreated was 57, which is highly relevant in a disease where increasing age is a factor.

“In addition, there is no control intervention which is common practice.  The investigators should have used placebo solutions, for instance water as a rinse and nasal infusion.  There is a well-known and well-studied placebo response, including from my own research, which can be large and in the order of 30 per cent.

“Having extensively studied Povidone Iodine (PI), published findings suggest it behaves badly in the mouth as it is rapidly inactivated by salivary proteins and I would suspect that the same applies to nasal secretions.  It’s also notable that the PI group showed adverse thyroid function effects.  This has been reported with mouthrinses of PI at only 1 per cent and in this study some concentrations, albeit in an ointment, were at 10 per cent.

“What is very clear from the data is that over time the carriage of the virus reduced over time in both the treated and control groups with very little difference between the two groups.  This would be typical of many viral infections, including the common cold.  Thus, the included subjects only tested positive for coronavirus but were not seriously symptomatic and certainly not considered for hospitalisation.  Essentially, all the investigators were reporting was the natural progression of Covid 19 infections over time and almost certainly independent of PI intervention.”



‘Povidone Iodine Mouthwash, Gargle, and Nasal Spray to Reduce Nasopharyngeal Viral Load in Patients With COVID-19: A Randomized Clinical Trial’ by Jeremy Guenezan et al. was published in JAMA Otolaryngology – Head & Neck Surgery at 16:00 UK time on Thursday 4 February 2021.

DOI: 10.1001/jamaoto.2020.5490



Declared interests

Prof Martin Addy: “I have no conflicts of interest in respect of my review and comments on this PI study.”

None others received.

in this section

filter RoundUps by year

search by tag