After analyzing data from the first human papillomavirus vaccination program in Australia, researchers have found that the vaccine offers significant protection against cervical abnormalities. This is according to a study published in the BMJ.
Human papillomavirus (HPV) is a virus that can affect human skin and the moist membranes that line the body, such as the cervix, anus, mouth and throat.
The virus can cause genital warts - the most common sexually transmitted infection - and cause changes to cells in the cervix that can lead to cervical cancer. According to the National Cancer Institute, cervical cancer - of which there are expected to be 12,340 new cases this year - is almost always caused by HPV infection.
At present, there are two HPV vaccines available worldwide - Gardasil and Cervarix. Studies have shown that both vaccines are effective in preventing cervical cancer in young women, as well as genital warts and high-grade anal disease in men.
But the researchers of this most recent study, including Prof. David Whiteman of the QIMR Berghofer Medical Research Institute in Australia, say there is little known about how these vaccines perform when administered within a wider population.
In April 2007, Australia became the first country to introduce a publicly funded national HPV vaccination program for girls aged 12 and 13 years.
A "catch-up" program also ran from 2007 until 2009. This offered the HPV vaccination to school girls aged 12-17 and women aged 18-26 years in general practice and community settings.
The HPV vaccination is designed to be administered in three doses over a 6-month period, although studies have suggested that two doses can offer similar protection against cervical cancer.
HPV vaccine effectiveness assessed in more than 100,000 women
Using data from population registers, the team assessed the effectiveness of the HPV vaccination against cervical abnormalities for female residents of Queensland, Australia, who had their first ever smear test between 2007 and 2011.
The researchers identified 103,353 women who were eligible for inclusion in the study and divided them into three groups.
The "high-grade" group was made up of 1,062 women whose smear test and follow-up biopsy showed precancerous abnormalities. The "other cases" group included 10,887 women who did not meet the high-grade definition but had other abnormalities, while the "control" group included 96,404 women with negative smear tests.
Women in both the high-grade cases group and the other cases group were older, less likely to live in major cities and more disadvantaged, compared with women in the control group.
Of the women in the high-grade cases group, 11% had been fully vaccinated, while 19% of women in the other cases group and 24% in the control group had been fully vaccinated.
Vaccine offers significant protection against cervical cancer
From their analysis, the researchers estimated that 4 years after the HPV vaccination program was implemented, three doses of the HPV vaccine provided 46% protection against high-grade cervical abnormalities and 34% protection against other cervical abnormalities for women who had no previous screening history.
The investigators estimated that two doses of the HPV vaccination provided 21% protection against high-grade and other cervical abnormalities. One dose of the vaccine did not provide significant protection against any cervical abnormalities.
Further analysis revealed that of the study subjects, 125 women needed to be vaccinated with three doses in order to prevent one high-grade cervical abnormality at the first smear test, while 22 women needed three vaccination doses in order to prevent one "other" cervical abnormality at the first screening.
The researchers note that the number of women who needed to be vaccinated to prevent one high-grade cervical abnormality was much lower among women who had previous screening history, compared with women who had not been screened before.
The investigators say this is likely to be because the incidence of high-grade cervical abnormalities is high among women who have had one or more prior smear tests.
Among women who had previously undergone one or more smear tests before the date of their abnormal smear test, vaccine effectiveness was found to be lower, compared with women who had no prior smear tests.
The researchers hypothesize this is because women who were already undergoing screening were sexually active and more likely to be infected with HPV before they received the vaccination.
Commenting on the findings, the study authors say:
"At present, cervical screening will remain necessary in vaccinated populations owing to the relative type specificity of current vaccines. Falling population prevalence of cervical abnormalities will reduce the sensitivity and positive predictive value of cytological testing, and screening programs will need to adapt to maintain their effectiveness.
Our data suggest that this task is now becoming more urgent given the relatively rapid impact of the vaccine on disease in the real world setting."
They add that continued observation is needed for women receiving the HPV vaccination, as the results may have implications for cervical screening recommendations.
In January this year, Medical News Today reported on the signs and symptoms of cervical cancer to look out for and the importance of regular cervical cancer screening.