I think there hasn't been enough research on iota-carageenan nasal sprays for prevention of viral infection for things more infectious than common colds. There was one study aimed at COVID-19 prophylaxis with it in hospital workers which was really promising: "The incidence of COVID-19 differs significantly between subjects receiving the nasal spray with I-C (2 of 196 [1.0%]) and those receiving placebo (10 of 198 [5.0%]). Relative risk reduction: 79.8% (95% CI 5.3 to 95.4; p=0.03). Absolute risk reduction: 4% (95% CI 0.6 to 7.4)."
There was one clinical trial afterwards which set out to test the same thing but I can't tell what's going on with it now, the last update was posted over a year ago. So we have one study which looks great but could be a fluke, and there's no replication in sight.
The good thing about carageenan-based products is that they're likely to be safe, since they're extensively studied due to their use as food additives and in other things. From Wikipedia: "Carrageenans or carrageenins [...] are a family of natural linear sulfated polysaccharides. [...] Carrageenans are widely used in the food industry, for their gelling, thickening, and stabilizing properties." See this section of the article for more.
If it really does work for COVID and is replicated with existing variants, that's already a huge public health win - there's still a large amount of disability, death and suffering coming from it. With respect to influenza, theres's some evidence for efficacy in mice and the authors of that paper say that it "should be tested for prevention and treatment of influenza A in clinical trials in humans."
If it has broad-spectrum antiviral properties then it's also a potential tool for future pandemics. Finally, it's generic and not patented so you'd expect a lack of research funding for it relative to pharmaceutical drugs.
I think there hasn't been enough research on iota-carageenan nasal sprays for prevention of viral infection for things more infectious than common colds. There was one study aimed at COVID-19 prophylaxis with it in hospital workers which was really promising: "The incidence of COVID-19 differs significantly between subjects receiving the nasal spray with I-C (2 of 196 [1.0%]) and those receiving placebo (10 of 198 [5.0%]). Relative risk reduction: 79.8% (95% CI 5.3 to 95.4; p=0.03). Absolute risk reduction: 4% (95% CI 0.6 to 7.4)."
There was one clinical trial afterwards which set out to test the same thing but I can't tell what's going on with it now, the last update was posted over a year ago. So we have one study which looks great but could be a fluke, and there's no replication in sight.
The good thing about carageenan-based products is that they're likely to be safe, since they're extensively studied due to their use as food additives and in other things. From Wikipedia: "Carrageenans or carrageenins [...] are a family of natural linear sulfated polysaccharides. [...] Carrageenans are widely used in the food industry, for their gelling, thickening, and stabilizing properties." See this section of the article for more.
If it really does work for COVID and is replicated with existing variants, that's already a huge public health win - there's still a large amount of disability, death and suffering coming from it. With respect to influenza, theres's some evidence for efficacy in mice and the authors of that paper say that it "should be tested for prevention and treatment of influenza A in clinical trials in humans."
If it has broad-spectrum antiviral properties then it's also a potential tool for future pandemics. Finally, it's generic and not patented so you'd expect a lack of research funding for it relative to pharmaceutical drugs.