Trends in classifying vaccine hesitancy reasons reported in the WHO/UNICEF Joint Reporting Form, 2014-2017: Use and comparability of the Vaccine Hesitancy Matrix.

Since 2014, the World Health Organization (WHO) member states have been annually reporting vaccine hesitancy reasons, using the WHO/UNICEF Joint Reporting Form (JRF). The Vaccine Hesitancy Matrix (VHM), developed by a WHO strategic advisory group of experts, can serve as an important tool to categorize vaccine hesitancy reasons reported in the JRF. We aimed to describe the reasons for vaccine hesitancy reported globally from 2014 to 2017 to ascertain trends over time and understand the comparability of using the VHM to classify hesitancy reasons from 2014 to 2016 based on previously published literature. We conducted a quantitative content analysis to code and categorize vaccine hesitancy reasons reported in the JRF from 2014 to 2017. Vaccine hesitancy trends were consistent from 2014 to 2017, where vaccine hesitancy reasons were mainly related to "individual and group level influences" (59%) followed by "contextual influences" (25%), and "vaccine- or vaccination-specific issues" (16%). Comparability of our approach to categorize vaccine hesitancy to the previously published JRF data showed that results were mostly but not entirely consistent. Major differences in categorizing vaccine hesitancy were noted between two specific reasons - "experience with past vaccination" (under "individual and group influences") and "risk/benefit- scientific evidence" (under "vaccine and vaccination-specific issues"); this was usually due to lack of clear definitions in some sub-categories and generic responses reported in the JRF. The JRF hesitancy module may benefit from modifications to improve the data quality. Understanding global vaccine hesitancy is crucial and JRF can serve as an important tool, especially with the potential introduction of a COVID-19 vaccine.