It's been a bad couple of days for Rule Breakers pick Vertex Pharmaceuticals (NASDAQ:VRTX) by the looks of the 23% fall in its share price since Thursday.

Friday marked the start of the American Association for the Study of Liver Disease (AASLD) conference, and many of the potential competitors for Vertex's hepatitis C virus (HCV) drug telaprevir are presenting new data at the conference.

Most media outlets attributed the fall in shares of Vertex on Friday to positive data from privately held Romark Laboratories, with its HCV drug candidate in phase 2 testing.

Romark announced that its thiazolide drug reduced the HCV virus below a detectable level in 79% of genotype 4 patients 12 weeks after treatment ended. This compares favorably to Vertex's telaprevir 60% range of subjects with undetectable virus levels after a similar length of treatment, but followed for 24 weeks after treatment ended.

The Romark data is interesting and definitely worthy of further follow-up. However, since it was tested in genotype 4 HCV patients, whereas the telaprevir results are in the much tougher to treat genotype 1 subtype of hepatitis C patients, it's not exactly an apples-to-apples comparison.

What subtype of HCV that a drug is tested in matters, because patients with the different subtypes have different responses to treatment. For example, the standard of care for current hepatitis C treatment is Roche's interferon Pegasys. In one study with Pegasys testing two different doses, 82% and 63% of genotype 4 patients were cured of their hepatitis C, whereas only 51% and 40% of genotype 1 patients were cured, so clearly genotype 4 patients responded to treatment better than genotype 1 patients.

Drugs that are effective in treating genotype 1 are usually effective in the other genotypes as well. Since about 70% (2.8 million) of patients in the U.S. have genotype 1 HCV, compared to only 2% (80,000) of patients with genotype 4, most drugmakers target the larger genotype 1 subgroup first.

As I mentioned last week, there will be competitors to telaprevir on the market after it gets approved. The data that Vertex presented during the AASLD conference only confirms what Rule Breakers analyst Charly Travers thought about the drug when he first recommended Vertex for the newsletter back in February 2005 (shares are still up more than 100% since then).

Shares of Vertex will gyrate up and down whenever competitors release new data, such as occurred with Schering-Plough's (NYSE:SGP) boceprevir a few weeks ago. As analysts waffle over the odds of these other drugs getting approved, there will be volatility in shares of Vertex, but it doesn't reduce the very strong likelihood that Vertex's telaprevir will be the first new anti-HCV treatment on the market in years.

Fool contributor Brian Lawler does not own shares of any company mentioned in this article. The Fool's disclosure policy is a blockbuster.