The vaccine targeting the four most frequent cancer-causing types of human papilloma virus (HPV) also reduces the risk of developing pre-cancerous cervical lesions caused by ten other types of HPV, according to findings presented today at the 47th Interscience Conference on Antimicrobial Agents and Chemotherapy.
The vaccine being studied, called Gardasil, has been shown to provide 100% protection against the development of pre-cancerous cervical and vulval lesions caused by HPV types 6, 11, 16 and 18 in women not previously infected with HPV.
Gardasil is licensed in Europe for children and adolescents aged 9 to 15 and women aged 16 to 26 for prevention of cervical cancer and other cellular changes associated with HPV infection, including genital warts.
The analysis presented today looked at the incidence of pre-cancerous lesions caused by ten other types of HPV (31, 33, 35, 39, 45, 51, 52, 56, 58, 59) in women who participated in the FUTURE I and II studies.
Epidemiological surveys suggest that these cancer-causing form, or `oncotypes`, account for around 16% of cases of cervical cancer in Europe and up to 22% of cases in other parts of the world.
The study analysed women who were not infected with either the HPV types covered by the vaccine or the ten other oncotypes upon entry to the study. Women received three doses of the vaccine at day 1, month 2 and month 6, and then underwent cervicovaginal DNA sampling and PAP smears at six to twelve month intervals for up to four years.
The analysis reported on cases of persistent infection, defined as two positive diagnoses of the same HPV type at least six months apart.
Out of 1036 women analysed, 41 cases of infection with HPV 31 or 45 occurred in the vaccine group, compared with 73 in the placebo group, a protective efficacy of 45% for the vaccine against infection with these oncotypes (95% confidence interval 18 – 63%).
When protection against a wider range of oncotypes was assessed (31, 33, 45, 52 and 58) protective efficacy fell to 28% (95% CI 7% – 44%).
The analysis also examined the protective effect against development of pre-cancerous lesions (cervical intraepithelial neoplasia grade 2 or 3) or malignancy confined to the surface cells of the cervix (AIS).
The protective efficacy against these changes was 62% for lesions caused by HPV 31 or 45 (95% CI 10 – 85), and 43% for HPV types 31, 33, 45, 52 and 58 (95% CI 7 – 66%).
Not all of these lesions would progress to cervical cancer, and the confidence intervals of the efficacy estimates are wide, but the findings nevertheless indicate that the Gardasil vaccine may protect against a wider range of cancer-causing HPV types than those included in the vaccine.
However the study cannot say anything about the potential protective effect against cancers caused by these HPV types in women already exposed to HPV at the time of vaccination, nor in women who are HIV-positive.
Another HPV vaccine also targeting types 16 and 18, Cervarix, does not clear established HPV infection in women, a large study reported recently, and the previously published analysis of the FUTURE I and II studies showed a protective efficacy of 20% in preventing cervical lesions caused by any sort of HPV (including 16 and 18) in women already exposed to HPV.
Brown D et al. HPV type 6/11/16/18 vaccine: first analysis of cross-protection against persistent infection, cervical intraepithelial neoplasia (CIN), and adenocarcinoma in situ (AIS) caused by oncogenic HPV types in addition to 16/18. 47th Interscience Conference on Antimicrobial Agents and Chemotherapy, Chicago, abstract G-1720b, 2007.