Writing in The Lancet Infectious Diseases , lead author Craig Coleman from the University of Connecticut School of Pharmacy, reports the results of combining 14 different studies.
In one of the studies, echinacea taken in combination with vitamin C reduced cold incidence by 86 per cent, and when the herbal was used alone the incidence of cold was reduced by 65 per cent.
A much-publicised study in the New England Journal of Medicine in July 2005 concluded that the herb did not have a significant effect on infection with a rhinovirus, but the methodology has been strongly questioned by herbal experts.
In particular, the study did not use a commercially available product, and dosage was lower than the standard dose in the US - 1g per day compared to 3g. Data from Euromonitor International indicates that such studies have taken a toll on sales.
The market researcher saw a peak in UK retail sales of echinacea in 2003 at €6.1m, falling to €4.9m in 2005.
Its projections are at odds with the retailers', expecting a compound annual growth rare of -2.8 per cent through to 2010.
Euromonitor's view on Western Europe as a whole is more positive, with 2005 sales at €163.7, in 2005 (down from €166 in 2004) and projected CAGR of 0.9 per cent through to 2010.
But even though this is positive growth, it is still up against projected CAGR of 4.4 per cent for the entire dietary supplements category.
The researchers note that over 200 viruses are capable of causing the common cold, and that they only monitored the focussed on studies looking at rhinovirus.
In addition to cutting the incidence of the common cold, recovery from the cold was also speeded up, they said, by cutting the duration of colds by 1.5 days.
Coleman and co-workers called for more research to verify the safety of the numerous different formulations that are commercially available.
Commenting independently on the research Professor Ron Cutler from the University of East London told the BBC: "The true benefits, and more importantly, how the agents work remains unclear and further better-controlled actual clinical trials still have to be carried out."
"There has also been the suggestion in the past that continuous treatment with echinacea is not recommended - the benefits may only be effective for one or two weeks and after taking the agent for this time people should stop and give the immune system a week without the agent."
Professor Ronald Eccles, director of the Common Cold Centre at the University of Cardiff, is also quoted by the BBC as saying the study was "a significant step in our battle against the common cold."
"Harnessing the power of our own immune system to fight common infections with herbal medicines such as echinacea is now given more validity with this interesting scientific evaluation of past clinical trials," he added.
******************* Reader comments: "The supplemental data package to the NEJM study, it is shown that the echinacea used in the study was devoid of phenolics.
This does not represent what is being sold on the market.
The NEJM study was an embarrasment to science and it would appear that it was either designed to fail or the authors failed to adequately research the phytochemistry and pharmacology of the product prior to study design.
If they had, they would have realized commercial products contain phenolics and dosages used by herbal practitioners are much higher than those used in the study."
- James Neal-Kababick, Flora Research Laboratories, Oregon