Alnylam (Nasdaq: ALNY) has presented the first proof of concept that RNAi works in humans, but I'd like to see proof that it actually cures a disease before I consider it a viable therapeutic.

The drug, ALN-RSV01, is used to treat infections from RSV, the respiratory syncytial virus that causes cold-like symptoms. Unfortunately, RSV symptoms can get much worse; they account for 300,000 hospitalizations per year in the U.S., mostly in patients with weak immune systems.

In a trial dubbed Gemini, healthy adults were given ALN-RSV01 for two days, purposely infected with RSV, and then given the drug for three more days. The drug is designed to inhibit the production of a protein used to form the virus, through a process called RNAi (RNA is the precursor to proteins and the "i" stands for interference).

In January, the company said the results were positive, but this was the first look at the data from the trial. The drug showed a 38% reduction in infection rate of the subjects and almost twice as many subjects remained free of infection compared to placebo.

Those are pretty good results, but I'm not sure it has an application to the real world. Since there's no way to know when a patient is going to be infected, it's a little hard to administer the drug two days before someone gets the virus. I guess it could be used as a prophylactic -- much like AstraZeneca's (NYSE: AZN) Synagis is used to treat high-risk infants -- but treating the infection once it's started is clearly where the big money is at.

The real test of RNAi will come in a phase 2 trial that will test ALN-RSV01 in naturally infected patients; it should begin in the first half of this year. Hopefully, if it's successful, Alnylam will give it a better name than ALN-RSV01.

I haven't been a huge fan of RNAi. Like everyone else, I think there's potential for it as a treatment, but investors and pharmaceutical collaborators such as Merck (NYSE: MRK), Biogen Idec (Nasdaq: BIIB), and Novartis (NYSE: NVS) have put lofty valuations on a therapy that's largely unproven. Call me conservative, but I remember how much potential there was for gene therapy -- and look at how those investments have gone.

More Foolishness about RNA -- DNA's little brother:

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Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. Biogen is a pick of the Stock Advisor newsletter. The Fool has a disclosure policy.