TORONTO - Canadian women who want to be immunized against HPV, a family of viruses that causes cervical cancer, now have a choice of two competing vaccines.
Health Canada has approved Cervarix, a product of GlaxoSmithKline Inc., which is expected to be available by the end of the month. Gardasil, a product of Merck Canada, has been on the market since 2006.
"The vaccines are different but we can't say one is clearly better than the other because we have no clinical head-to-head studies," said Dr. Barbara Romanowski, an infectious diseases specialist at the University of Alberta in Edmonton.
Cervarix is designed to protect against infection with two strains of human papillomavirus, HPV 16 and 18. It also offers some protection against HPV 31, 33 and 45.
Between them, those strains account for more than 80 per cent of cases of cervical cancer.
Gardasil is designed to prevent infection with four strains of HPV: 6, 11, 16 and 18. The latter two strains are responsible for more than 70 per cent of cases of cervical cancer, while the other two cause about 90 per cent of cases of genital warts. (There are almost 200 strains of HPV. In addition to cervical cancer, human papillomavirus can cause throat cancer, cancer of the head and neck, anal cancer, penile cancer and other cancers of the female genital tract such as vulvar and vaginal cancer.)
Romanowski, who has received research funding from GSK, said the choice of vaccine depends on a woman's age and lifestyle.
She said Cervarix offers "superb protection for cervical cancer" while Gardasil offers "very good protection for cervical cancer and genital warts."
The competing vaccines are similarly priced, with a retail price of about $400. Each vaccine requires three doses.
The National Advisory Committee on Immunization recommends that all girls and women aged nine to 26 be vaccinated against HPV.
In Canada, every province and territory offers school-based vaccination but the age group targeted varies by jurisdiction, from Grade 4 in Quebec through to Grade 8 in Ontario.
Currently, all school-based programs use Gardasil, but GSK officials said they are in discussions with several provinces and territories.
Merck officials said they have shipped about 2.2 million doses of the vaccine.
Human papillomavirus is one of the most common sexually transmitted infections so vaccination is recommended before girls become sexually active.
However, the vaccines can offer protection against cervical cancer to women who are sexually active and even those who have had abnormal Pap tests.
The vaccines are not designed to replace Pap testing but rather to reduce the number of cases of cervical cancer, cervical lesions and genital warts.
About four million Canadian women undergo Pap testing each year. There are approximately 325,000 abnormal Pap tests, which can require biopsies and surgery.