vantiss @vantiss@treehouse.systems
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I think this is the best writeup I've seen on the (lack of) evidence for the efficacy of nasal sprays as a "layer of protection" against /

There is a lot of misinformation out there about nasal sprays preventing COVID-19. Unfortunately, there are no convincing studies showing that nasal sprays prevent COVID-19. The published studies investigating whether or not nasal sprays prevent COVID-19 each have major issues, which I will detail here.

I have a PhD in biochemistry and one of my PhD projects was on COVID-19. The main takeaway of this post is that there is no sound evidence that nasal sprays prevent COVID-19. Thus, nasal sprays should not be used for COVID-19 prevention in place of effective measures such as high-quality well-fitting respirators, ventilation and air purification.

1. As a brief overview, some major issues with these studies include: The fact that the test spray and not the placebo spray contain ingredients that can cause false-negative COVID-19 tests (combined with no information on the timing between applying nasal sprays and taking nasal/nasopharyngeal swabs for COVID-19 tests) Ex: a heparin nasal spray can cause false-negative COVID-19 RT-PCR tests (study A) and carrageenan from vaginal swabs after using carrageenan-containing lube can cause false-negative PCR tests for HPV (study B). If we take the estimate from another paper (study C) that nasal sprays get immediately diluted approximately 1:1 by nasal fluid (when the spray volume in each nostril is 0.100 mL), then the amount of carrageenan in a nasal swab taken immediately after spraying the nasal spray is comparable to that in the carrageenan undiluted samples in experiment 4 in study B. Those samples from study B all produced false-negative PCR tests for HPV. Lack of placebo spray, participants having to seek out the test spray themselves (suggesting they may take more precautions than those in the study taking no spray, not even a placebo) Lack of sufficient information for reproducibility (especially regarding what is considered a positive and a negative COVID-19 RT-PCR test result) Lack of testing for asymptomatic/presymptomatic infections (how can we say something prevents COVID-19 if we aren’t testing for asymptomatic and presymptomatic COVID-19 infections?)1. As a brief overview, some major issues with these studies include: The fact that the test spray and not the placebo spray contain ingredients that can cause false-negative COVID-19 tests (combined with no information on the timing between applying nasal sprays and taking nasal/nasopharyngeal swabs for COVID-19 tests) Ex: a heparin nasal spray can cause false-negative COVID-19 RT-PCR tests (study A) and carrageenan from vaginal swabs after using carrageenan-containing lube can cause false-negative PCR tests for HPV (study B). If we take the estimate from another paper (study C) that nasal sprays get immediately diluted approximately 1:1 by nasal fluid (when the spray volume in each nostril is 0.100 mL), then the amount of carrageenan in a nasal swab taken immediately after spraying the nasal spray is comparable to that in the carrageenan undiluted samples in experiment 4 in study B. Those samples from study B all produced false-negative PCR tests for HPV. Lack of placebo spray, participants having to seek out the test spray themselves (suggesting they may take more precautions than those in the study taking no spray, not even a placebo) Lack of sufficient information for reproducibility (especially regarding what is considered a positive and a negative COVID-19 RT-PCR test result) Lack of testing for asymptomatic/presymptomatic infections (how can we say something prevents COVID-19 if we aren’t testing for asymptomatic and presymptomatic COVID-19 infections?)
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