Carrageenan nasal spray may double the rate of recovery from coronavirus and influenza virus infections: re-analysis of randomized trial data

Abstract Carrageenan is a sulfated polysaccharide that has been extensively used in food products. Since the 1980s, carrageenan has been shown to prevent infections due to several viruses in cell cultures, including rhinoviruses which cause the common cold. In animal studies it prevented mortality caused by influenza A. Carrageenan is generally regarded as safe by the FDA. This individual patient data meta-analysis examined the datasets of two randomized placebo-controlled trials which investigated the effect of carrageenan separately on children and adults. In both trials, iota-carrageenan was administered nasally 3 times per day for 7 days for patients with the common cold and follow-up lasted for 21 days. Nasal carrageenan increased the recovery rate from all colds by 54% (95% CI 15% to 105%; P = 0.003). The increase in recovery rate was 140% in coronavirus infections, 119% in influenza A infections, and 70% in rhinovirus infections. We used quantile regression to calculate the effect of carrageenan on colds of differing lengths, by dividing the distribution into 5 quintiles. The mean duration of colds in the placebo groups of the first four quintiles were 4.0, 6.8, 8.8 and 13.7 days, respectively. The fifth quintile contained patients with censored data. The 13.7-day colds were shortened by 3.8 days (28% reduction), and 8.8-day colds by 1.3 days (15% reduction). Carrageenan had no meaningful effect on shorter colds. In the placebo group, 21 patients had colds that lasted over 20 days, compared with 6 patients in the carrageenan group. This corresponds to a 71% (P = 0.003) reduction in the risk of longer colds. Finally, in the placebo group, 37 patients had recurring cold symptoms after first being cured, compared with 16 in the carrageenan group. This corresponds to a 56% (P = 0.002) reduction in the risk of recurring symptoms. Given that carrageenan has an effect on diverse virus groups, and its demonstrated effects on two old coronaviruses, it seems plausible that nasal carrageenan may also have an effect on the new coronavirus SARS-CoV-2. Further research on nasal iota-carrageenan is warranted.