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

OBJECTIVE: 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.

METHODS: 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.

RESULTS: 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.

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

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