The number of new cases of genital warts in women and heterosexual men under 21 has fallen dramatically in Melbourne in the wake of the Australian HPV vaccination programme using a quadrivalent vaccine.

In April 2007, Australia introduced a vaccination programme for girls and young women aged 12-27 years using a vaccine against HPV genotypes 6, 11, 16 and 18. The HPV types 6 and 11 are known to cause anogenital warts and are not known to be carcinogenic whereas genotypes 16 and 18 cause 70% of the cases of cervical cancer in women and are also known to be acquired sexually.

The researchers looked at the number of cases of genital warts diagnosed from the beginning of July 2004 to the end of June 2011 at the Melbourne Sexual Health Centre (MSHC). The patient management system used at MSHC routinely collects clinical and epidemiological data on the attendees of this open-access, walk-in triage sexual health clinic that serves a population of about 4 million.

Of the 52,454 new patients seen at MSHC during the study period 5,021, 9.6% (95% CI: 9.3%-9.8%) were diagnosed with genital warts.

From July 2004 to June 2007, the proportions of patients with genital warts either increased or did not change in all groups.

The largest decline in genital warts was between 2007/2008 and 2010/2011 and occurred in women under the age of 21 (from 18.6% to 1.9%) and in heterosexual men in the same age group (from 22.9% to 2.9%). From July 2010 to the end of June 2011, only four cases of genital warts were diagnosed in heterosexual women under 21 years compared with between 46 and 66 cases per year before July 2007.

After July 2007, diagnosis of genital warts also decreased significantly, but by a smaller extent, in women and heterosexual men aged 22-29 years. However, there were no significant changes in women and heterosexual men aged 30 years or more, men who have sex with men or non-residents.

The authors comment that their results support their earlier study which looked at MSHC data up to the end of 2008 and also the findings of the Australia-wide surveillance programme. Furthermore, their analyses were adjusted for the number of sexual partners in the previous year.

Although the observations strongly suggest a relationship with the vaccination programme, there may have been confounders that also contributed to the reduction in genital warts such as changes in condom use.

It is possible for women who were not vaccinated and not diagnosed at the time of the study to develop genital warts up to 45 months after acquisition of the HPV type 6 DNA.

The Department of Health (DH) in England commenced a vaccination programme in September 2008 for girls aged 12 to 13 years to protect them from acquiring carcinogenic HPV types 16 and 18 before they become sexually active. The DH has announced recently that the quadrivalent vaccine will be used in the programme from September 2012. Unfortunately, the effect on cervical cancer may not be evident until at least 10 to 20 years later. The effect on reduction of genital warts, however, may be sooner as this paper suggests.

Dr Richard Ma