New York Times 21 August 2008
Two vaccines against cervical cancer are being widely used without sufficient evidence about whether they are worth their high cost or even whether they will effectively stop women from getting the disease, two articles in this week’s New England Journal of Medicineconclude. Both vaccines target the human papillomavirus, a common sexually transmitted virus that usually causes no symptoms and is cleared by the immune system, but which can in very rare cases become chronic and cause cervical cancer.
The two vaccines, Gardasil by Merck Sharp & Dohme and Cervarix by GlaxoSmithKline, target two strains of the virus that together cause an estimated 70 percent of cervical cancers. Gardasil also prevents infection with two other strains that cause some proportion of genital warts. Both vaccines have become quick best sellers since they were licensed two years ago in the United States and Europe, given to tens of millions of girls and women. “Despite great expectations and promising results of clinical trials, we still lack sufficient evidence of an effective vaccine against cervical cancer,” Dr. Charlotte J. Haug, editor of The Journal of the Norwegian Medical Association, wrote in an editorial in Thursday’s issue of The New England Journal. “With so many essential questions still unanswered, there is good reason to be cautious.”
In her article, Dr. Haug points out the vaccines have been studied for a relatively short period — both were licensed in 2006 and have been studied in clinical trails for at most six and a half years. Researchers have not yet demonstrated how long the immunity will last, or whether eliminating some strains of cancer-causing virus will decrease the body’s natural immunity to other strains. More to the point, because cervical cancer develops only after years of chronic infection with HPV, Dr. Haug said there was not yet absolute proof that protection against these two strains of the virus would ultimately reduce rates of cervical cancer — although in theory it should do so.
Dr. Richard Haupt, medical director of Merck, called these concerns “very theoretical,” noting that continuing research and monitoring suggested that immunity would be longlasting and that the vaccine would not lead to problems with other strains.