Treatment of the non-placebo group involved using a nasal spray containing carrageenan (a sulphated polysaccharide found in red seaweed/algae) three times per day for 7 days. Cold symptoms were found to resolve 2.1 days faster and viral loads in the nasal washings were significantly decreased compared to placebo group. At day 21 of observation, one sixth of patients given the placebo were still ill, while only one twentieth were in the treatment group.
Personally, I would like to see larger studies conducted by other independent groups to verify the findings.
So how does this nasal spray work?
The problem with the common cold is that there are SO many viruses that manifest the same disease including rhinovirus, coronavirus, parainfluenza, influenza, respiratory syncytial virus, adenovirus, enterovirus, and metapneumovirus. As such, an effective treatment should be able to disable all these virus types and not just one.
The way carrageenan works is by sticking to the virus regardless of type and preventing it from attaching to the nasal lining. As such, the virus is unable to enter into the body and cause problems. It essentially blocks the virus like the wall of a castle.
The caveat is that in order for this nasal spray to work, you have to start using the medication as soon as cold symptoms appear (within 2 days). Remember... it works by blocking the virus from entering the body. If you wait too long, the virus has already entered the body making any type of blocking medication ineffective.
Where can you buy it?
It is available over-the-counter in most European countries and Canada. But NOT available in the United States.
The nasal spray is made by Marinomed in Europe using their Mavirex technology and also licensed for marketing/distribution by Boehringer. Carragelose is the brand name of the carrageenan ingredient. Depending on the country, the actual name of the nasal spray is sold under is different.
For example, in England, the nasal spray is called "Cold and Flu Defence Nasal Spray".
To make sure you have the right nasal spray, look under ingredients and make sure carragelose is listed.
On another note... Afrin nasal spray has also been shown to have some anti-viral activity in unpublished reports. Just be aware to not use it more than 3 days or else you may get addicted to it.
Efficacy of a Carrageenan nasal spray in patients with common cold: a randomized controlled trial. Respiratory Research 2013, 14:124 doi:10.1186/1465-9921-14-124
Efficacy and safety of an antiviral Iota-Carrageenan nasal spray: a randomized, double-blind, placebo-controlled exploratory study in volunteers with early symptoms of the common cold. Respir Res 2010. doi:10.1186/1465-9921-11-108
Lessons learned from a double-blind randomised placebo-controlled study with a iota-carrageenan nasal spray as medical device in children with acute symptoms of common cold. BMC Complement Altern Med 2012. doi:10.1186/1472-6882-12-147