Women who are diagnosed with pre-cancerous cervical conditions after receiving the HPV vaccine can still benefit from a considerably reduced risk of reoccurring disease, a study published today on bmj.com shows.
A team of international researchers studied data involving 1350 women from 24 developed and developing countries across the world. All of the women were between the ages of 15 and 26 between 2001 and 2003. They had had either human papillomavirus (HPV) quadrivalent vaccine or placebo during one of two randomised controlled trials and were then diagnosed with HPV-related vaginal or vulval diseases (including genital warts) or had cervical surgery. A total of more than 17,000 women took part in the two trials and were followed for approximately four years, but this new study looks only at those women who then developed HPV-related disease.
Previous studies have shown that HPV vaccination does not reduce progression to cervical pre-cancers in women with ongoing infections at the time of vaccination. However, no studies to date have looked at the impact of HPV vaccination in preventing subsequent disease after treatment for such pre-cancers. This new study aimed to see if the vaccine decreased the risk of developing subsequent disease after the first definitive treatment.
Among women who needed cervical surgery after the trials, the risk of getting any subsequent HPV related disease was 6.6 cases per 100 woman per year among the 587 women who had had HPV vaccine. For the 763 women who had had placebo the risk was 12.2 cases per 100 woman per year. So vaccinated women had 46.2% less risk (the reduced risk ranged between 22.5% to 63.2% using a measure called the 95% confidence interval). In addition, vaccination was associated with a significant reduction in risk of any subsequent high grade disease of the cervix by 64.9% (20.1% to 86.3%).
For the women who were diagnosed with vaginal or vulvar disease the reduction in risk of any HPV disease after diagnosis and treatment among those who had had HPV vaccine was 35.2% (13.8% to 51.8%).
In conclusion, the authors reinforce that vaccination does not reduce progression to disease in women who are infected with HPV at the time of vaccination, but vaccinated women who developed disease after taking part in these randomised controlled trials had less frequent subsequent disease, so vaccination offered substantial benefit. The authors suggest that only long-term surveillance of the vaccinated population can "determine the population effectiveness of vaccination" and state that there are several programmes currently in place to monitor the safety and impact of HPV vaccines on subsequent diseases.
In an accompanying editorial, Dr Jane Kim from the Harvard School of Public Health says that clear communication of the beneficial yet complex properties of HPV vaccines is crucial to ensure that effective and successful decisions can be made on HPV vaccination worldwide.