Web sites holding a favorable view toward the vaccination practice provide more vaccination-specific information themes compared to the neutral vaccination-related online sources. The anti-vaccination subset, however, has proved to include vaccination-specific information and services features as much as the other two subsets without significant differences. Comparing the scores on the aggregated Vaccination Specific Content Index of the three groups based on the webpage’s general tone, a statistically significant difference (
p < .05) was observed [F(2.1090) = 3.59,
p = 0.028]. Post hoc comparison using the Tukey HSD test showed that the mean Vaccination Specific Content Index score for pro-vaccination webpages (M = 5.95, SD = 2.06,
p = 0.02) was significantly higher than the webpages that were neutral (or undefined) toward the vaccination practice (M = 5.37, SD = 2.60). Remarkably, the maximum score achievable and reported of fulfilling all the 9 vaccination-specific categories was attained by the anti-vaccination subset of webpages (e.g.,
http://www.prisonplanet.com/myth-busted-vaccinations-are-not-immunizations.html). In detail, neutral webpages conveyed less
disease information (40 %) than both pro- and anti-vaccination subsets (58 and 52 %, respectively),
p = 0.001.
Treatment information was delivered more by the pro-vaccination subset (83 %), compared to both anti-vaccination and neutral (or undefined) webpages (64 and 63 %, respectively),
p < 0.001.
Benefits, and risks of vaccination were present in both pro-, and anti-vaccination webpages (79 and 83 %, respectively), but not as much for the subset being neutral (or undefined) in regard to vaccination (56 %),
p < 0.001. As expected,
benefits of vaccination were persistently treated by pro-vaccination webpages (75.3 % of the total sample’s subset). About 30 % of neutral, and 10 % of anti-vaccination webpages delivered the benefits derived by immunizations,
p < 0.001. Conversely,
severe risks of vaccination were insistently promoted by anti-vaccination webpages (78 % of the total subset of the sample), followed by the neutral (or undefined) subset (50 %). One fifth of pro-vaccination webpages advanced the sub-topic (or theme) of the serious complications potentially caused by several immunizations,
p < 0.001. The provision of
terms’ definitions and Q&A formats was significantly less frequent in anti-vaccination webpages (only 16 %), as compared to both pro-vaccination (29 %) and neutral subsets (35 %),
p < 0.001. The inclusion of external
links to other vaccination-related web sources was, as estimated, a central component for all the subsets of webpages investigated (around 85 % to 90 % each subset). In particular, a positive relationship was observed between a favorable tone toward the vaccination practice and the provision of external links to
other pro-vaccination sources (77 %),
p < 0.001. About half of neutral (or undefined), and one quarter of anti-vaccination webpages reviewed were externally linked with further pro-vaccination websites. On the other hand, external
links to supplementary
anti-vaccination websites were positively correlated with the negative tone of the webpage (83 %),
p < 0.001. About 60 % of neutral (or undefined), and only 4 % of pro-vaccination webpages offered links to external anti-vaccination websites.