Readability and Reliability of Online Information on Childhood Vaccination: A Cross-Typology Analysis

Childhood vaccination remains a cornerstone of public health, but parental decisions are increasingly influenced by online information. While the internet offers widespread access to vaccine-related content, its readability, quality, and reliability are often questionable. This study evaluated 147 publicly available English-language websites providing information on childhood vaccination, categorized into five types: government, professional organizations, commercial, health portals, and scientific journals. Readability was assessed using four standard indices (Flesch-Kincaid Grade Level [FKGL], Gunning FOG Index, Simple Measure of Gobbledygook [SMOG], and Automated Readability Index [ARI]), while quality and reliability were evaluated using the DISCERN tool, JAMA benchmarks, and HONcode certification. Most websites exceeded the recommended sixth-grade reading level, potentially limiting accessibility. Government and professional organization sites scored highest in quality and reliability but were not always the most readable. Commercial sites consistently scored lowest across all domains. Only 18% of the websites had valid HONcode certification, indicating limited ethical oversight. A moderate negative correlation (ρ = -0.38) was found between readability and quality, suggesting that more complex texts tend to be of higher quality but less accessible. These findings highlight a critical challenge in digital health communication: the need to balance clarity with credibility. Enhancing both the comprehensibility and trustworthiness of online vaccination content is essential to support informed decision-making and strengthen public vaccine confidence.