Parents' Uptake of Human Papillomavirus Vaccines for Their Children: A Systematic Review and Meta-Analysis of Observational Studies

"[L]imited evidence documents factors associated with parents' uptake of HPV vaccines for their children, particularly outside North America."

In addition to structural and health system issues that contribute to low coverage of human papillomavirus (HPV) vaccines globally, the broader context of vaccine hesitancy suggests that parents' knowledge, attitudes, and beliefs about HPV and vaccines may have a substantial influence on uptake. This systematic review and meta-analysis focuses on parents' uptake of HPV vaccines for their children (18 years or younger), more than 10 years after initial licensure of an HPV vaccine. It assesses correlates of parents' HPV vaccine uptake for their children, rather than proxies such as HPV vaccine acceptability or intention to vaccinate.

The researchers conducted a comprehensive search across multiple electronic databases to locate studies meeting the inclusion criteria; the last search date was November 2017. They included randomised controlled trials (RCTs), cluster RCTs, non-RCTs, longitudinal studies, cohort studies, and cross-sectional studies, and there were no language, geographical, or time restrictions.

Seventy-nine studies on 840,838 parents across 15 countries were included. The pooled proportion of parents' uptake of HPV vaccines for their children was 41.5% (range: 0.7%-92.8%), twofold higher for girls (46.5%) than for boys (20.3%). The disparities in uptake by sex of child are consistent with the later approval and recommendation of HPV vaccination for boys than girls in the United States (US), where the majority (69.6%) of studies were conducted, and the lack of coverage of HPV vaccination for boys in many other national insurance programmes.

In the meta-analysis of 62 studies, and in line with previous descriptive reviews largely focused on uptake for girls, physician recommendation had the single greatest effect on parents' uptake of HPV vaccines for their children, supported by evidence from over 20 studies. Results also indicate a substantial negative effect of parents' concerns about HPV vaccine safety on HPV vaccine uptake for their children, as well as positive effects of belief in vaccines in general and perceived HPV vaccine benefits; each of these factors is supported by findings from 10 or more studies. Routine child preventive check-up was identified across 8 studies as being positively associated with parents' HPV vaccine uptake for their children. Health-insurance-covered HPV vaccination and lower out-of-pocket cost also had significant effects on uptake.

Some highlights and action points to emerge from the researchers' reflection on the findings:

• The findings highlight the importance of physicians making recommendations - especially for boys, particularly in the context of the enduring perception that HPV is a woman's concern.
• Parental attitudes and beliefs about vaccines in general, and HPV vaccines in particular, may be strategic targets for both physician engagement with parents and for public health education campaigns in accelerating HPV vaccine uptake. In the context of even greater scrutiny that may be applied to an adolescent vaccine for a sexually transmitted infection (STI), careful and respectful healthcare provider engagement with parents is recommended. The positive impact of parents' trust in healthcare providers on their uptake of HPV vaccines for their children provides evidence to support the importance of the process of physician engagement in effectively communicating with parents.
• Findings from this review suggest a substantive focus on addressing parents' HPV vaccine safety concerns and supporting their positive beliefs in the health benefits of vaccines in general, as well as explaining the particular benefits of HPV vaccines for their children, including boys and girls.

The researchers outline limitations and areas for future research. For example, they urge expansion of investigations in low- and middle-income countries (LMICs), which have the highest morbidity due to HPV-related cancers and the lowest access to and uptake of HPV vaccines. In addition, "Further research including intervention studies and longitudinal designs, with results disaggregated by sex of children and parents, and by HPV vaccine initiation versus series (now two-dose) completion, is needed....Evidence-informed strategies that contribute to accelerating HPV vaccine uptake are critical to realising the full public health potential of HPV vaccines on cancer prevention."