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• Decline in genital warts in Melbourne: How much is really due to the implementation of the Australian national quadrivalent human papillomavirus vaccination programme?
  Marie-Claude Boily
  Published on: 13 May 2016

• Published on: 13 May 2016

  Decline in genital warts in Melbourne: How much is really due to the implementation of the Australian national quadrivalent human papillomavirus vaccination programme?

  • Marie-Claude Boily, Senior lecturer
  • Other Contributors:
    • Marc Brisson, Catherine M Lowndes

  We read the article by Fairley et al(1) with great interest. The authors concluded that the decline in genital warts among women in the age groups (<28 years) targeted for vaccination provides strong evidence for the population-level effectiveness of the vaccine. They also report that this conclusion was strengthened by the fact that no significant decline in genital warts post vaccination has been noted among other ri...

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  We read the article by Fairley et al(1) with great interest. The authors concluded that the decline in genital warts among women in the age groups (<28 years) targeted for vaccination provides strong evidence for the population-level effectiveness of the vaccine. They also report that this conclusion was strengthened by the fact that no significant decline in genital warts post vaccination has been noted among other risk groups (e.g. men who have sex with men (MSM) who have not been targeted for vaccination, and women >=28 years) other than men who have sex with women (MSW). In addition to the authors' discussion about their study limitations, we would like to highlight a few issues that suggest that the data should be interpreted carefully.

  Using trends from sexual health clinics to assess changes following the introduction of a vaccination program may be misleading because this type of data is amenable to different sources of biases especially that the impact is measured only one year after the start of the vaccination programme.

  Although the authors mention that there have been "no changes in clinic policy either relating to the selection of clients attending the centre or clinical management and diagnosis", this does not guarantee that the clientele has not changed. For example, using the data from table 1(1) to derive the denominator in each risk population, one realizes that the annual number of clients attending the clinic started increasing after 2006, after a period mostly stable or declining, especially among MSM and women age <28 years (~ 19% increase between 2006-2008). This shows that a change in the number of attendances has occurred around the time that the HPV vaccine was licensed in 2006.

  In table 2(1), the authors interpret the fact that (in addition to women age <28) the only statistically significant change, 5.0% decline in the quarterly fraction of patients presenting with genital warts, was among MSW as further evidence of the role of the vaccination program since MSW may have benefited from the indirect impact of female vaccination. However, since the number of MSM in the sample is three times less than the number of MSW, it is also possible that the non-significant 5.9% decline reported among MSM is simply due to a lack of statistical power. If this was the case, this would beg the question as to why the fraction of cases would have declined among MSM.

  This information combined suggests that it is possible that the client population presenting to the clinic may also have changed following the licensing of the HPV vaccine, and especially after the beginning of the vaccination programme. Indeed, the publicity around the licensing of the new vaccine and the information and ad campaigns accompanying the launch of the vaccination program may have changed the health seeking behaviour of patients with HPV-related disease. The vaccination program may have increased awareness and/or change the risk perception and anxiety related to the disease. However, the direction of the potential bias is difficult to predict as it may differentially affect those with or without symptoms, vaccinated or not and could even be transient. Thus, it would have been informative from Fairley et al's(1) to also present trends in gonorrhoea prevalence, which is the usual marker of change in sexual behaviour, rather than new HSV-2 cases(2), as well as trends in the number of partners or other risk behaviour for each risk groups presented, which seemed to have been available.

  Nevertheless, these are encouraging preliminary results, which should be interpreted carefully due to their limitations, especially after such a short time following the start of the programme (one year). It is important to continue the monitoring and evaluation of the programme over many years and to confirm these types of results with additional data source. Although, ideally, one would want data from representative random samples of the general population, this will only be possible in rare instances where cross-sectional studies of the general population are repeatedly carried out at regular interval (e.g. NHANES(3)) as this is difficult and expensive.

  Instead it may be easier to collect more frequently data from convenience samples of different risk populations, or to use population- level consultation data (i.e. medical billings), which however are also not immune from biases. In order to help the interpretation of time trends of the primary disease outcomes of interest it would therefore be highly desirable to complement this information with data on HPV vaccination status and socio-demographics characteristics and even if challenging, if at all feasible, basic sexual behaviour data.

  Given the current attention given to the systematic evaluation of intervention programme to help decision making, it is important to carefully think about the formal evaluation of HPV vaccination programme.

  References

  (1) Fairley CK, Hocking JS, Gurrin LC, Chen MY, Donovan B, Bradshaw BC. Rapid decline in presentations of genital warts after the implementation of a national quadrivalent human papillomavirus vaccination programme for young women. Sex Transm Infect 2009;85:499-502 Published Online First: 16 October 2009

  (2) Page KR, Moore RD, Wilgus B, et al. Neisseria gonorrhea and Chlamydia trachomatis Among Human Immunodeficiency Virus-Infected Women Sex Transm Dis. 2008, 35(10): 859-861.

  (3) Dunne EF, Unger ER, Sternberg M et al Prevalence of HPV infection among females in the United States JAMA 2007, 297(8): 813-819.

  Conflict of Interest:

  None declared

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  Conflict of Interest:
  None declared.

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