2012 Antigen Review for the New Zealand National Immunisation Schedule: Human papillomavirus

Abstract

This report summarises new research into human papillomavirus (HPV) vaccines and vaccination published during the past four years. Most HPV infections are cleared within 18 months. However, clearing an infection does not necessarily lead to immunity and reinfection is possible. HPV types 6 and 11 account for around 90% of all genital warts cases and can also cause recurrent respiratory papillomatosis. The casual link between human papillomaviruses and cervical cancer was made in the 1980s. Since then it has been shown that virtually all cervical cancers could be attributed to the sexual transmission of around 12 oncogenic types, in particular HPV types 16 and 18. In countries without effective cervical screening programmes cervical cancer is a leading cause of cancer death. It is now also recognised that these high risk HPV types are associated with anal cancer, vulvar cancer, vaginal cancer, penile cancer and HPV-positive oropharyngeal cancer. In 2009 there were 107 cases of cervical cancer, accounting for 1.5% of female cancer registrations and 1.1% of female cancer deaths in New Zealand (NZ); it is the third most common cancer by incidence and fifth most common cancer mortality among NZ women. A further 185 cases of other cancers, including those affecting males, which were likely associated with the HPV-16 and -18 were also registered. Overall, an estimated 292 cases of cancer in 2009 were potentially preventable by vaccination against HPV-16 and -18. The relatively low rate of cervical cancer registrations compared with other cancers is largely attributable to the cervical screening programme. Ethnic disparities in cancer registrations and mortality still existed in 2009 however, disparity in mortality had reduced. Since 2007 two vaccines have been available to prevent infection by some HPV types. Both vaccines protect against HPV-16 and -18 while a quadrivalent vaccine (HPV4) also protects against HPV-6 and -11. Vaccination against human papillomavirus has the potential to reduce both the incidence of associated cancers and with respect to the HPV4 vaccine, HPV associated genital warts. Both vaccines are highly immunogenic in virtually all vaccinees and highly efficacious against persistent infection and cervical disease in recipients previously uninfected. However, the vaccines are not able to prevent disease caused by existing infection. For this reason it is recommended that vaccination occurs prior to the onset of sexual activity. New Zealand introduced an HPV immunisation programme in September 2008 providing a funded vaccine to girls and young women born in 1990 and 1991. The programme was extended in 2009 to girls and women born from 1992. The routine programme is offered primarily through a school-based programme to girls in year eight (aged 12 – 13 years). Decreases in new cases of genital warts in women under 20 years of age were already being observed by Auckland Sexual Health Service by 2010. The impact of HPV4 vaccine on new cases of genital warts has been observed in many countries who have introduced the vaccine including NZ. Generally reductions are most profound in the population targeted by vaccination programmes and to a significant but lesser extent the population forming their sexual partners. Sexual health clinics in Melbourne, Australia have observed a near elimination of new cases of genital warts in their female population under 25 years of age and note that the reproduction number may have fallen below one. This means that genital warts could well be eradicated among this population. In contrast there have been no changes in the incidence of new cases of genital warts observed in older women or men who have sex with men — those populations not targeted for vaccination and their sexual partners. The reduction in prevalence in infections caused by the vaccine-types of HPV provides further support for the role of herd immunity provided by HPV vaccination. The safety of HPV vaccines was evaluated in very large randomised placebo controlled trials, and reactogenicity and safety are well established. The past four years has focused on close monitoring of post licensure surveillance for events too rare to be detected in the pivotal studies. Extensive data from very large populations that includes data for millions of vaccinees word wide support the excellent safety profiles of these vaccines. Post marketing surveillance systems globally continue to monitor the safety of HPV vaccination programmes. Both HPV vaccines are highly immunogenic. To date anamnestic responses have been demonstrated in vaccine recipients out to 8.5 years. There is no evidence of waning immunity. HPV2 vaccine induces a more robust immune response than HPV4 against types 16 and 18. The clinical importance of this is not known; however there appears to be superior cross protection against non-vaccine oncogenic types offered by the bivalent vaccine. The value of this additional protection against cancer causing HPV types needs to be weighed against the impact on genital warts offered by HPV4. Vaccination of women who have had procedures for pre-existing cervical diseases there has been shown to be beneficial through a reduction in subsequent procedures. Very few women are co-infected with multiple vaccine types at any one time. As the only women who can derive no protection from vaccination are those already infected with all vaccine types there are no benefits to screening prior to vaccination. Vaccination of older women is efficacious. The vaccination of males, including those with HIV infection, has been demonstrated to be efficacious against HPV-associated cancers and genital warts. Currently men who have sex with men are deriving no benefit from vaccination programmes that target only females. Modelling the impact of HPV vaccination against cervical cancer supports vaccinating at an early age prior to sexual debut and vaccinating males, particularly if coverage of females is relatively low. Of particular relevance to NZ is the very early age of sexual debut reported. Data from the NZ Youth 2007 survey indicates over 20% of NZ adolescents have had sexual intercourse before the age of 13 years. This had increased to nearly 40% by the age of 15 years and over 50% by age 17 years. Rates are higher for Māori. Most HPV infections occur within the first two years of onset of sexual activity with more than 40% becoming infected during this period. As the first sexual relationship carries a substantial risk of exposure to HPV an important point to consider for the NZ schedule is timing, and consideration should be given to brining the age for vaccination forward to include more girls prior to onset of first sexual activity. There are no further vaccine options other than HPV2 and HPV4 available at this time. A nine-valent vaccine has completed phase three studies and results are anticipated. The co-administration of HPV vaccine with other vaccines has been shown to be safe and immunogenic. The non-inferiority of a two-dose schedule in the younger age group noted to date is worthy of consideration and the flexibility of schedules may make programme delivery easier.