Five may be more than four, but I'm not sure it's going to help GlaxoSmithKline (NYSE:GSK) muscle its way into the human papillomavirus (HPV) vaccine space. Today the company published an article in The Lancet showing that its vaccine, Cervarix, protects against five different strains of HPV.

Merck's (NYSE:MRK) Gardasil protects against only four strains of HPV, but I'm not sure the data is going to be enough to overcome Merck's lead. Vaccines like those made by Novartis (NYSE:NVS), Wyeth (NYSE:WYE), sanofi-aventis (NYSE:SNY), and others are hard to unseat. Doctors get used to using certain vaccines and then sales just perpetuate themselves.

The four strains versus five strains isn't cut and dried, either. The two strains that both vaccines protect against cover 70% of the cervical cancer cases. Gardasil's two-additional-strain-protection covers 90% of genital warts, while Cervarix's three additional strains add 11%-16% of additional protection from cervical cancer.

Even if Glaxo is able to grab some of Merck's U.S. market share -- if Cervarix is approved by the Food and Drug Administration later this year -- there isn't as much to be had. The low-hanging fruit is all but gone in the U.S., since Merck has already grabbed many of the females aged 9 to 26.

 

2006

2007

2008

U.S. sales of Gardasil (in millions)

$235

$1,194

$1,041

Year-over-year increase (decrease)

N/A

408%

(13%)

Source: company releases.

In the first quarter of this year, U.S. Gardasil sales continued to tumble, with sales down 39% year over year. There's some potential for a bump in sales if the FDA approves Gardasil for use in males, but, from an economic standpoint, that use might not be worth it.

There will, of course, be a new group of young women to vaccinate every year, so sales aren't going to go to zero, but Glaxo has clearly missed the boat.

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Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. The Fool has a disclosure policy.