An infodemic is an enormous flow of inaccurate information that may spread through social media, potentially causing confusion and damaging peoples’ behavior and health, during an epidemic. It may intensify outbreaks and hinder the discovery of trustworthy sources and reliable guidance for populations. Our aim was to characterize the individual engagement performance of social media posts published before and during the Covid-19 pandemic (before and after vaccination) on Facebook’s pages of selected national health organizations to identify typologies of agencies. Publicly available data on 39525 posts from 17 health agencies Facebook pages between 01/01/2019 and 31/05/2022 was studied with univariate, bivariate, and multivariate exploratory data analysis (such as principal components and hierarchical cluster analysis) and text mining methodologies. Results showed that globally Covid-19 led to a relevant increase in the number of posts published on the health agencies’ Facebook pages under study, and to a significant increase in their audiences’ interactions. However, engagement during the pandemic period after starting the vaccination decreased, when compared with the previous pandemic period. Furthermore, 3 typologies of agencies were identified: agencies with high performance in total interactions; agencies with either higher or lower relative engagement; agencies with opposing performance before and after vaccination started during the pandemic period. Hence, audiences sought more information on Facebook with the Covid-19 pandemic. Different performances from health agencies’ pages may be linked to different infodemic strategies. Our study provides valuable insights to health agencies, as infodemic management should not be confined to times of crisis but should be an ongoing investment and may contribute to more effective health promotion strategies.