Rationale and Background:
HPV vaccination programmes have been shown to reduce not only HPV infection but also the incidence of cervical cancer. However, uncertainty remains on the real-world effectiveness of different brands, and dose schedules.
Research Questions and Objectives:
To generate evidence from real-world data on the effectiveness of HPV vaccination in preventing severe disease outcomes in women, including invasive cervical cancer and CIN2+, for the different licensed HPV vaccines in Europe. This study will include data sources from UK, Spain and Germany.
More specifically the study objectives are:
Main objectives:
• To assess the effectiveness of HPV vaccination in prevention of invasive cervical cancer stratified by licenced vaccine brand
• To assess the effectiveness of HPV vaccination in prevention of CIN2+, stratified by licenced vaccine brand
• To assess the effectiveness of HPV vaccination in prevention of conization, stratified by licenced vaccine brand
Secondary objectives:
• To assess the effectiveness of HPV vaccination overall for the three outcomes (i.e. invasive cervical cancer, CIN2+ and conization)
• To assess the effectiveness of HPV vaccination in prevention of invasive cervical cancer, CIN2+ and conization in subgroups defined by number of doses, within each brand.
Results in both main and explanatory analyses will be further stratified by age group.
Research Methods
The target trial emulation approach will be used for this non-interventional study. The summary of the Target Trial is as follows:
• Study primary objective: to investigate the effectiveness of HPV vaccines to prevent cervix cancer.
• Estimand:
• Population: Women eligible for vaccination according to eligibility criteria in each country. More generally, females 9 years old or older any date after the launch of the vaccination programme in the corresponding country.
• Treatments:
• Placebo (unvaccinated).
• Vaccinated with Gardasil/Silgard.
• Vaccinated with Cervarix
• Vaccinated with Gardasil-9.
Patients are randomised to one of the above groups in a 1:1:1:1 ratio.
• Variable/outcome: incidence of invasive cervical cancer within 5, 10 and 15 years of vaccination.
• Summary measure: incidence rate. Comparison of interest is incidence rate ratio between every vaccinated group and the unvaccinated group.
• Intercurrent events:
• For the unvaccinated: vaccination, dealt with a hypothetical strategy. To implement this, data from women in the unvaccinated group that at some point get vaccinated will be included in the analysis up to the time of vaccination. (This means in the analysis these women will be censored at the time of vaccination.)
• For the vaccinated, any group: treatment discontinuation (i.e. not receiving all scheduled doses), dealt with a treatment policy strategy. To implement this strategy, all available data from these women will be included in the analysis regardless of treatment discontinuation.
f. Statistical methods: The incidence rate ratio between each vaccinated group and the unvaccinated group will be estimated.
Study Design:
New user matched cohort study
Population:
All females aged 9 years or older on any date after the launch of the vaccination programme in any of the contributing datasets and with at least 365 days of prior data availability at the beginning of vaccination programme launch date in their country of residence will be eligible. The analysis will be further restricted to matched cohorts of vaccinated and unvaccinated participants with similar baseline characteristics (see ‘Data Analysis’).
Data Sources:
– Primary care records from the UK (Clinical Practice Research Datalink (CPRD) GOLD) and Catalonia, Spain (Information System for Research in Primary Care (SIDIAP)); outpatient primary care and specialist data from Germany (IQVIA Disease Analyzer (DA) Germany)
Study Period:
HPV national vaccination programs have different start dates. For CPRD, the study period will begin on 1/1/2008. For SIDIAP and IQVIA DA Germany, the study period will begin on 1/1/2007.
For all databases, the end year of the study period is the most recent data available, sometime in 2023.
Eligibility criteria
Eligibility for vaccination in each country. More generally, females >9yo any date after the launch of the vaccination programme in the corresponding country.
Exposure
Assignment procedures: Vaccination status (brand and number of doses) is assigned as seen in the data at 15 years old. Unvaccinated will be assigned as not being vaccinated at 15 years old and censored when (and if) they get vaccinated later on.
Brand: For those vaccinated, brand will be primarily assigned as brand of all the doses administered before 15. Women with heterologous brand (not the same brand for each dose) schedules will be excluded. If this information is not available, it will be inferred, when possible, using each country’s vaccination schedules.
Schedules: Unvaccinated, vaccinated with 1 dose, vaccinated with 2 doses , and vaccinated with 3 doses.
Outcome
The main outcome of interest is invasive cervical cancer. Two secondary outcomes are also considered: CIN2+ and Conization. These outcomes will be phenotyped and diagnostics will be carried out.
Follow-up
Follow up will start at the moment of the administration of first dose before 15 years old. For unvaccinated, the follow up will start at the same date as their vaccinated matched counterpart. Follow-up will extend until another vaccine dose or outcome event, end of available follow-up, or death of any individual of the matched pair, whichever comes first.
Other variables
Year of birth, calendar year, age at vaccination, cytology results from smear test prior to the first dose of vaccine if available. For LASSO regression, all recorded features recorded in the database, including socio-demographics, geographic location, healthcare resource use, comorbidity, medicine/s use, previous smear testing, and previous vaccination/s.
Data Analysis
All analyses will be conducted separately for each database, and carried out in a federated manner, with effectiveness estimates meta-analysed and the I2 heterogeneity coefficient reported.
We will conduct a propensity score (PS) matched cohort design, where target and comparator cohort participants will be matched 1:5. Matching will be done based on PS, year of birth, year of first dose (for analyses not involving dose number) and geographic region using nearest neighbour matching, with calliper width 0.2 standard deviations as is standard for propensity score matching. Large-scale PS will be estimated using lasso regression to estimate the probability of being in the target cohorts, potentially including any of the covariates mentioned above.
The following matched cohorts will be compared:
Main comparisons:
Vaccinated vs unvaccinated per brand:
• Vaccinated with Gardasil/Silgard (target) (1 or more dose) vs unvaccinated (comparator)
• Vaccinated with Cervarix (target) (1 or more dose) vs unvaccinated (comparator)
• Vaccinated with Gardasil-9 (target) (1 or more dose) vs unvaccinated (comparator)
Secondary comparisons:
Vaccinated (target) (1 or more dose) (any brand) vs unvaccinated (comparator) overall.
Dose comparisons:
• Vaccinated with 2 or more doses (target) vs 1 dose (comparator) of the same brand.
• Vaccinated with 3 or more doses (target) vs 2 doses (comparator) of the same brand.
Vaccine effectiveness analyses
Incidence rates and incidence rate ratios (IRR) will be calculated for the matched cohorts and outcomes at 5, 10 and 15 years (if enough follow-up is available). Cox proportional hazard models will be used to calculate hazard ratios (HR) for time-to-event analyses.