The objective of a study was to measure the effectiveness of the quadrivalent human papillomavirus ( HPV ) vaccine against cervical abnormalities four years after implementation of a nationally funded vaccination programme in Queensland, Australia.
Participants were women eligible for free vaccination ( aged 12-26 years in 2007 ) and attending for their first cervical smear test during the period 2007-2011.
High grade cases were women with histologically confirmed high grade cervical abnormalities ( n=1062 ) and other cases were women with any other abnormality at cytology or histology ( n=10 887 ).
Controls were women with normal cytology ( n=96 404 ).
The main outcome measures were exposure odds ratio ( ratio of odds of antecedent vaccination [ one, two, or three vaccine doses compared with no doses ] among cases compared with controls ), vaccine effectiveness ( [1−adjusted odds ratio ] ×100 ), and number needed to vaccinate to prevent one cervical abnormality at first screening round.
Researchers stratified by four age groups adjusted for follow-up time, year of birth, and measures of socioeconomic status and remoteness.
The primary analysis concerned women whose first ever smear test defined their status as a case or a control.
The adjusted odds ratio for exposure to three doses of HPV vaccine compared with no vaccine was 0.54 for high grade cases and 0.66 for other cases compared with controls with normal cytology, equating to vaccine effectiveness of 46% and 34%, respectively.
The adjusted numbers needed to vaccinate were 125 and 22, respectively. The adjusted exposure odds ratios for two vaccine doses were 0.79 for high grade cases and 0.79 for other cases, equating to vaccine effectiveness of 21%.
In conclusion, the quadrivalent HPV vaccine conferred statistically significant protection against cervical abnormalities in young women who had not started screening before the implementation of the vaccination programme in Queensland, Australia. ( Xagena )
Crowe E et al, BMJ 2014;348:g1458