Enrolment of young women attending cervical cancer screening to survey effectiveness of HPV vaccination
In his letter, W. Tjalma expresses concerns regarding cervical screening in Belgium before the age of 25 . Having authored the European Guidelines for Quality Assurance in Cervical Cancer Screening and/or acted as advisor for the development of Belgian recommendations for cervical cancer prevention, we confirm that screening of women before the age of 25 years is generally not cost-effective and potentially harmful . Although not recommended, the reality is that a relatively large proportion of younger women in Belgium do have Pap smears taken . In the period 2002–2006, the proportion of women with a Pap smear within the previous 3 years, was 17% and 51%, in age groups 15–19 and 20–24, respectively .
In 2010–2014, we conducted the SEHIB study (Surveillance of the Effects of HPV Immunisation in Belgium), which recruited women aged 18–64 years participating in cervical cancer screening. Women were enrolled consecutively to avoid selection bias. SEHIB aimed at estimating the burden of type-specific HPV infection and cervical lesions in the entire screening population as well as early HPV vaccination effects in women younger than thirty . The study protocol was approved by ethical committees of four universities and by an international board of experts in HPV vaccination surveillance and was in agreement with WHO and European recommendations  and . SEHIB demonstrated lower rates of HPV16 and HPV18 infection as well as cervical precancerous lesions associated with these types in vaccinated than in non-vaccinated women aged 25 and younger . The observed protective effects of HPV vaccination for the aimed outcomes were similar to those of the intention-to-treat analyses of randomized trials and within ranges reported in other surveillance studies .
During the SEHIB study, young women were never encouraged to have a Pap smear taken for the only reason of enrollment in SEHIB. We do share Tjalma’s concerns related to screening at too young age. However, we consider his contention that SEHIB induced over-screening in women <25 years as well as his criticism on study methods and findings as not justified. Nonetheless, we are aware that future vaccine impact monitoring may be improved by linking population-based cervical cancer screening and HPV vaccination registries, completed with targeted HPV genotyping . To contribute in this task, a Belgian HPV Reference Centre was recently set up. Impact of HPV vaccination on cancer incidence is planned but was not an aimed early effect of the SEHIB study.
Conflict of interest
MA received support from the 7th Framework Program of DG Research of the European Commission through the CoheaHr Project [Grant number 603019].
An unrestricted grant was provided by Sanofi-Pasteur-MSD to the University of Ghent who coordinated the SEHIB study. The grant was given in the framework of the EMA (European Medicine Agency) request to set up post-marketing surveillance of HPV vaccination effects in non-Nordic member states of the European Union.