Readability comparison of pro- and anti-HPV-vaccination online messages in Japan

In Japan, the HPV vaccination rate has sharply fallen to nearly 0% due to a series of sensational media reports of adverse events. Online anti-HPV-vaccination activists often warn readers of the vaccine's dangers. We aimed to examine distribution and readability of pro-and anti-vaccination online messages with relation to these authors' professional expertise.

We conducted online searches via two major search engines. Identified sites were classified as "anti," "pro," or "neutral" depending on their claims, and "health professional" or "non-health professional" depending on their authors' expertise. Readability was determined using a validated measure of Japanese readability. Statistical analysis was conducted using two-way analysis of variance and Tukey's test.

Of the total 270 sites analyzed, up to 137 (50.7%) were deemed anti- and 101 (37.4%) pro-HPV-vaccination. Of the pro-vaccination sites 71% were written by health professionals. Anti-vaccination messages were found to be considerably easier to read than pro-vaccination ones; both among those by health professionals and non-health professionals.

Our findings substantiate concern that the anti messages may serve to prolong the HPV vaccination crisis.

We recommend that health professionals use readability assessment tools and improve the text for easier reading if necessary.