Human papilloma virus (HPV) prophylactic vaccination: challenges for public health and implications for screening.

Prophylactic vaccination against high risk human papilloma virus (HPV) 16 and 18 represents an exciting means of protection against HPV related malignancy. However, this strategy alone, even if there is a level of cross protection against other oncogenic viruses, cannot completely prevent cervical cancer. In some developed countries cervical screening programmes have reduced the incidence of invasive cervical cancer by up to 80% although this decline has now reached a plateau with current cancers occurring in patients who have failed to attend for screening or where the sensitivity of the tests have proved inadequate. Cervical screening is inevitably associated with significant anxiety for the many women who require investigation and treatment following abnormal cervical cytology. However, it is vitally important to stress the need for continued cervical screening to complement vaccination in order to optimise prevention in vaccinees and prevent cervical cancer in older women where the value of vaccination is currently unclear. It is likely that vaccination will ultimately change the natural history of HPV disease by reducing the influence of the highly oncogenic types HPV 16 and 18. In the long term this is likely to lead to an increase in recommended screening intervals. HPV vaccination may also reduce the positive predictive value of cervical cytology by reducing the number of truly positive abnormal smears. Careful consideration is required to ensure vaccination occurs at an age when the vaccine is most effective immunologically and when uptake is likely to be high. Antibody titres following vaccination in girls 12-16 years have been shown to be significantly higher than in older women, favouring vaccination in early adolescence prior contact with the virus. Highest prevalence rates for HPV infection are seen following the onset of sexual activity and therefore vaccination would need to be given prior to sexual debut. Since 20% of adolescents are sexually active at the age of 14 years, vaccination has been suggested at 10-12 years. However, parental concerns over the sexual implications of HPV vaccination may reduce uptake of vaccination thereby reducing the efficacy of an HPV vaccination programme. Concerns have already been raised over the acceptability of a vaccine preventing a sexually transmitted infection in young adolescents, particularly amongst parents or communities who consider their children to be at low risk of infection. This may be a particularly sensitive issue for ethnic minority groups. This paper considers the factors which will influence the efficacy of a public HPV vaccination programme and its impact on cervical screening.