Dose-Response Relationship of a Web-Based Tailored Intervention Promoting Human Papillomavirus Vaccination: Process Evaluation of a Randomized Controlled Trial

"[T]his web-based, tailored intervention fits well with the mothers' needs and has the potential to increase HPV vaccination uptake."

In the Netherlands, human papillomavirus (HPV) vaccination uptake remains low (45.5% in 2017). To improve informed decision making (IDM) and HPV vaccination acceptability, a group of researchers systematically developed an interactive, web-based tailored intervention to which mothers of Dutch girls were invited to participate. They already reported results of the randomised controlled trial (RCT), which showed positive intervention effects on IDM, decisional conflict, and nearly all determinants of HPV vaccination uptake (for more details, see the first item under Related Summaries, below). The aim of the present study, a process evaluation, was to provide insight into the intervention's working mechanisms by evaluating: (i) programme use, (ii) programme acceptability, and (iii) the relationship of programme use with programme acceptability and intervention effects (i.e., dose-response relationship).

In brief (see also Related Summaries, below), the web-based intervention provided mothers with tailored feedback about topics on HPV vaccination, delivered by 2 virtual assistants. The website consisted of 4 menu options: (i) 2-sided, tailored information about HPV vaccination, (ii) a decisional balance in which mothers could weigh their perceived pros and cons, (iii) practical information, and (iv) frequently asked questions. Within menus i-iii, mothers could visit several components. In addition, mothers were given the opportunity to visit an "in-depth" information page within some of the components (e.g., educational movies).

For the purpose of the process evaluation, only participants from the experimental condition (i.e., those invited to use the web-based intervention; N=3,995) were included in the analyses. They were invited to visit the website of the web-based intervention between baseline (January 2015, just before access to the intervention) and follow up (March 2015, prior to the first HPV vaccination, in line with the national HPV vaccination round of 2015). Indicators for programme use were time of website use (i.e., duration of intervention exposure) and completeness (i.e., proportion of all available web pages visited by the mother while she was logged on to the website, ranging from 0% to 100%). HPV vaccination uptake registered by Praeventis, which is the national electronic vaccination register, was used as the primary outcome. Secondary outcomes were IDM, decisional conflict, and social-psychological determinants of HPV vaccination uptake.

On average, these invited mothers had a positive intention toward their daughters' HPV vaccination at baseline. Compared with the national HPV vaccination uptake at the time (i.e., 2015), uptake was higher in the study sample (73.17%, vs. 60.98%).

Among the 3,995 invited mothers, 2,509 (62.80%) logged on to the website, 2,239 of whom (89.24%) visited at least one page of the intervention components. On average, mothers spent 21.39 minutes on the website and completed 50.04% of the website components. Mothers visited the page "Ways to Protect Against Cervical Cancer" the most frequently, whereas they visited "Value Clarification" the least. "General Information" had the highest completion rate. Only a small percentage of the mothers visited in-depth information (comprising educational movies or extra information).

The overall acceptability of the intervention was rated 7.64 on a 10-point scale. Acceptability was significantly and positively associated with completeness; this did not account for time of website use. The virtual assistants were rated 7.41 on a 10-point scale. The mean scores on all other programme acceptability measures were moderate to high. Intention-to-treat analysis showed a significant positive effect of completeness on all outcome measures, including on HPV vaccination uptake. Time of website use had a significant positive effect on all outcomes, except for uptake, risk perception when not vaccinated, subjective norms, and habit.

In short, despite the fact that effect sizes were small overall, the more time mothers spent on the intervention, the more likely they were to make an informed decision, experience less decisional conflict, have a higher intention to vaccinate their daughter, have a more positive attitude, have more positive beliefs, have a lower risk perception of HPV vaccination, anticipate more feelings of regret about rejecting the HPV vaccine, report a higher relative effectiveness of the HPV vaccine, have higher self-efficacy expectations, and have more knowledge at follow-up.

Researchers' reflections on the findings include:

• Programme use: Almost two-thirds (62.80%) of the mothers who were invited to use the intervention logged in. This reach is adequate, but interest be sparked via other channels (e.g., the internet, social media). In addition, word-of-mouth recommendations could be encouraged by providing "tell-a-friend" services at the web-based intervention. Of the mothers who logged in to the intervention, a small portion of the mothers (10.76%) did not view any of the intervention's content; this is likely due to technical difficulties because at follow-up, some mothers (320, 12.75%) indicated they were not able to see or hear the virtual assistants.
• Use of intervention components - Mothers were most interested in the effectiveness of (alternative) methods to protect against cervical cancer (88.03% visited) and the risks of their daughter getting infected with HPV and developing cervical cancer (86.87% visited). These appear to be essential components of communication about HPV vaccination.
• Programme acceptability - The researchers attribute the intervention's high acceptability to the systematic and user-centred process by which it was developed - that is, the intended group was extensively involved. Not only did the researchers fine-tune the content of the intervention to the mothers' preferences and requirements but this also was considered in the design of the website.
• Effects of programme use on intervention outcomes - The researchers believe that the positive effects can be attributed to the extensive tailoring throughout the intervention. Support for this notion comes from the study results indicating that mothers perceived the intervention to be well-tailored (5.22 on a 7-point scale). Not only did the researchers tailor the content of the intervention to the mothers' personal interest, but it was also used to guide the mothers' personal route through the intervention. The latter is likely to have improved the usability of the intervention.

Recommendations based on these reflections include:

• Future interventions promoting HPV vaccination acceptance should: (i) incorporate a process evaluation alongside the effect evaluation, (ii) include strategies to arouse interest so as to expand reach, and (iii) include time on task.
• It could be useful to investigate the influence of different media types (e.g., graphic vs. nongraphic presentations) on decision-making about HPV vaccination. Cox and colleagues (2010) found that parents who viewed a graphic presentation of HPV-related risk information had a higher HPV vaccination intention compared to parents who viewed a nongraphic presentation.
• Future research could examine differences in use and acceptability in specific subgroups of participants - for example, by conducting moderation analyses with socio-demographics (e.g., educational level).
• Similar intervention models could be developed for: (a) groups other than mothers (e.g., daughters or sons in case they will become a next group for HPV vaccination) and (b) other vaccinations (e.g., maternal pertussis vaccination).

In conclusion: "Mothers who had completed more of the intervention were more likely to have their daughter vaccinated against HPV, and had higher levels of IDM and more positive scores on determinants of HPV vaccination acceptance. In particular, the effect on HPV vaccination uptake is an important finding, which was not found when simply contrasting the experimental to the control condition....This stresses the importance of conducting a process analysis alongside such an effect evaluation. These results are very promising, considering the currently low HPV vaccination uptake rates in the Netherlands." In fact, because of the intervention's adequate (dose-response) effects and acceptability, the intervention was incorporated into the national HPV vaccination communication alongside existing communication materials.