A new U-S study says a vaccine against the virus that causes cervical cancer is still effective after 41/2 years.

The study's author says, in fact, that one shot might be enough protection for a lifetime.

The study found no increased viral load in any of the 800 women who were tested 41/2 years after they were inoculated.

Previous studies have show the vaccine to be 100 percent effective in killing off papillomavirus types that cause more than 80 percent of cervical cancer cases.

Cervical cancer kills about a half million women a year worldwide and is second only to breast cancer when it comes to cancer deaths in females.

In Canada, about 400 women died of the disease each year.

The results of the study have been published in the online issue of the British medical journal The Lancet.