Abnormal Pap tests after the HPV vaccine

Worldwide, cervical cancer affects 500 000 women and causes 275 000 deaths annually. Persistent infection with one of 13 oncogenic types of human papillomavirus (HPV) is now known to be the cause of both squamous and adenocervical carcinomas of the cervix. The Pap test involves the examination of exfoliated cells from the cervix and has been shown to be an effective way of detecting the precursors of squamous cell carcinoma. In Australia, commencing in 2007, a free quadrivalent HPV vaccine was offered to all females aged 12-26 years.

This article looks at why a substantial number of young women who have been vaccinated with the HPV vaccine will still have Pap test abnormalities.

Prophylactic efficacy of the two HPV vaccines against specific HPV types is almost 100%. This knowledge has created an expectation of the demise of both cervical cancer and Pap test abnormalities. Efficacy of the vaccine is dependent upon the recipient not having been infected with that HPV type. It is likely that most of the women aged 18-26 years who have had the HPV vaccine were already sexually active and therefore exposed to one or more HPV types. We can still expect to see a substantial number of young vaccinated women with Pap test abnormalities, due to both HPV exposure before vaccination and to the many HPV types not covered by the vaccine. A noticeable reduction in cancers and Pap test abnormalities will not be seen for some years.