Human papillomavirus (HPV) is detected in 99.7% of cervical cancers. Current vaccines target types 16 and 18. Prior to vaccination implementation, a prospective cohort study was conducted to determine baseline HPV prevalence in unvaccinated women in Wales; after HPV16 and HPV18, HPV 51 was found to be most prevalent. This study aimed to re-assess the unexpected high prevalence of HPV 51 and consider its potential for type-replacement. Two hundred HPV 51 positive samples underwent re-analysis by repeating the original methodology using HPV 51 GP5+/6+ PCR-enzyme immunoassay, and additionally a novel assay of HPV 51 E7 PCR. Data were correlated with age, social deprivation and cytology. Direct repeat of HPV 51 PCR-EIA identified 146/195 (75.0%) samples as HPV 51 positive; E7 PCR identified 166/195 (85.1%) samples as HPV 51 positive. HPV 51 prevalence increased with cytological grade. The prevalence of HPV 51 in the pre-vaccinated population was truly high. E7 DNA assays may offer increased specificity for HPV genotyping. Cross-protection of current vaccines against less-prevalent HPV types warrants further study. This study highlights the need for longitudinal investigation into the prevalence of non-vaccine HPV types, especially those phylogenetically different to vaccine types for potential type-replacement. Ongoing surveillance will inform future vaccines.

Background Human papilloma virus (HPV) infection is known to be a necessary cause of cervical cancer and is found in 99.7% of invasive cervical carcinomas. Current HPV vaccines protect against infection from strains 16 and 18. Baseline prevalence studies are important for the measurement of prophylactic vaccine impact and type-replacement monitoring. Between 2009-2010 the HPV research group in collaboration with Cervical Screening Wales conducted the ‘Base HPV 2009 study’ to determine baseline prevalence in unvaccinated women aged 20-22 in Wales. Preliminary analysis of results showed that in single HPV infection, 16 was the most prevalent high-risk strain followed by 18 and 51. This high prevalence of HPV 51 has not been observed in previous studies from Wales and is not a common finding elsewhere. This study aims to determine whether the high prevalence of HPV 51 observed in the Base HPV 2009 study is a true finding and if HPV 51 should be considered a candidate for type-replacement post-vaccination. Methods The first 100 single and 100 multiple HPV 51 positive liquid-based cytology (LBC) samples from the Base HPV 2009 study were selected for re-analysis. Each sample underwent DNA extraction and was tested using two methods: 1) Repeat of original methodology using GP5+/6+ HPV 51 PCR-ELISA. 2) HPV 51 E7 PCR. Data were then correlated with age, social deprivation score and cytology. 5 samples were excluded from analysis. Results Direct repeat of HPV 51 PCR-EIA identified 146 of 195 (75.0%) samples as HPV 51 positive. E7 PCR identified 166 of 195 (85.1%) samples as HPV 51 positive. When classified by cytological grade, the prevalence of confirmed HPV 51 increased with grade. Conclusions This study confirms that the prevalence of HPV 51 observed in the Base HPV 2009 study population is truly high and warrants further consideration. There is limited evidence on the cross-protection for 51 offered by the current HPV vaccine and it represents a potential candidate for type-replacement following vaccination. This study highlights the need for further longitudinal investigation into the regional and global prevalence of HPV 51. The data would recommend HPV 51 to be considered in future multivalent vaccines.