World Health Organization is losing online credibility towards health-sensitive topics: Infodemiological analysis of Facebook users' reactions.

Background: The scientific infodemic constitutes one of the greatest threats to public health and safety today. The credibility of the main dissemination agencies is an essential tool for adhering to measures to preserve public health. Methods: The study is a longitudinal retrospective conducted on a web platform to investigate netizens' infodemic attitude towards World Health Organization. Reactions such as "like," "love," "affection," "surprise," "sadness," "anger," and "derision" were collected under World Health Organization (WHO) Facebook posts on climate change (from 2019 to 2022) and vaccines (from 2021 to 2022). Descriptive statistics, linear regression, and correlation methods were implemented to identify possible trends and relationships with the COVID-19 vaccination campaign. Results: These findings showed a worrying increase in derision reactions about climate change-related posts (up to 22% in November 2022, with a quadratically growing trend over time since December 2020). Furthermore, infodemic reactions such as anger and especially derision made up the majority of emotional reactions to vaccine-related posts since 2021 and up to 44% of total reactions in November 2022 (median since July 2021=9%, IQR: 4%-14%). Finally, there is evidence of a correlation between the start of the COVID-19 vaccination campaign and public distrust towards the WHO, even for issues unrelated to vaccines such as climate change. Conclusion: Based on what is known in the literature, these preliminary findings signal that the WHO is losing online public credibility towards extremely relevant issues for global health. Infodemiological interventions in accordance with the recent literature are urgently required.