A prestigious medical journal has raised questions regarding a new vaccine sold by Merck .
The New England Journal of Medicine said in an editorial Wednesday that Merck's Gardasil, a treatment for human papillomavirus or HPV, appears to be safe and effective but "a cautious approach may be warranted" due to unanswered questions about the drug's long-term effectiveness and potential for adverse effects that could emerge over time.
The medical journal also noted that it's difficult to show that early treatment of HPV prevents cancer, given the long period phase between exposure to HPV and development of disease.
"Correlation with the ultimate outcome -- cancer prevention-- will require the long-term observation of a large number of treated women," the journal said.
HPV is the leading cause of cervical cancer in women.
The editorial accompanied three studies published on Wednesday, which showed that Gardasil protects against cervical cancer caused by HPV for at least three years and also prevents potentially cancerous lesions.
Merck recently reported first-quarter Gardasil sales of $365 million. Prudential Equity Group projects Merck to post Gardasil sales of $1.6 billion and $2.2 billion in 2007 and 2008, respectively.
The company co-markets the vaccine, which was approved in the United States in June 2006, with Sanofi-Aventis in parts of Europe.
GlaxoSmithKline is expected to launch its delayed HPV vaccine Cervarix in the first half of 2008.