Table 1.

Social media platforms and their characteristics.

Social Media Platform	Start Year	Number of Monthly Active Users Worldwide in 2021 [117]	Characteristics	Dis/Misinformation Spread
Facebook	2004	2500 thousands of millions	Platform that allows users to upload, share and like various images, videos, live videos, stories, and specific pages.	It has deleted more than 20 million posts on its main social network and photo-sharing app Instagram for violating COVID-19 misinformation rules since the start of the pandemic. Facebook seeks to address criticism that its platforms have been used to spread fear about vaccines and misleading information about coronavirus. The company implemented new policies against COVID-19 misinformation, including a ban on repeat offenders spreading falsehoods and directing users to a central COVID-19 clearinghouse [118]. However, US President Joe Biden warned in July 2021 that the spread of misinformation about COVID-19 on social media is “killing people”, when questioned about the alleged role of “platforms like Facebook” in spreading falsehoods about vaccines and the pandemic [119].
YouTube	2005	2291 thousands of millions	Video sharing platform that allows users to upload, bookmark, and share videos.	YouTube said it removed 130,000 videos from its platform in 2020 and 2021 when it implemented a ban on content that spreads misinformation about COVID vaccines. Policy includes termination of antivaccine influencer accounts [119].
WhatsApp	2009	2000 thousands of millions	Instant messaging application for smartphones, in which messages are sent and received via the Internet, as well as images, videos, audio, audio recordings (voice notes), and calls and video calls with several participants at the same time, among other functions.	The ease of dissemination of messages from this social network and the relative anonymity that it provides to the first replicator of a chain message allows the sending of false and incomplete messages. In a study carried out in Zimbabwe countering misinformation through WhatsApp, it was found that potentially harmful behavior that does not comply with blocking guidelines decreased by 30 percentage points. The results show that social media posts from trusted sources can have substantially large effects not only on people’s knowledge but ultimately on related behavior [120]. Brazilian researchers questioned the role in the spread of the COVID-19 outbreak in their country and the disinformation through WhatsApp of President Bolsonaro’s narrative to minimize the impact of the disease in Brazil [121]
Instagram	2010	1000 thousand of millions	Image-sharing platform that allows users to upload, share, and like images and short videos.	An analysis of pages with hashtags frequently used by antivaccine conspirators found that general mistrust of vaccines was the most common, including the idea that the government and/or the media have fabricated or concealed information related to COVID-19. Conspiracy theories were the second most prevalent topic among the publications. In general, COVID-19 was frequently presented in association with beliefs that question authority [122]. A March 2021 report found that Instagram recommendations in the UK pushed users toward COVID disinformation, antivaccine content, and antisemitic material during the peak of the pandemic. Misinformation was most frequently displayed to new users who followed a combination of accounts on the platform that included leading personalities in the fight against vaccination or wellness influencers who disdained the efficacy of vaccines [123].
Twitter	2006	3295 thousands of millions	Platform that allows you to share short messages that can be accompanied by images.	Twitter introduced a feature in August 2021 that allows users to report misinformation they find on the platform, flagging it to the company as “misleading.” An exploratory study of my information found that false claims spread faster than partially false ones. Compared to a background corpus of COVID-19 tweets, misinformation tweets are more often concerned with discrediting other information on social media [124]. In August 2021, Twitter suspended 229 accounts and removed 5579 accounts that violated the antimisinformation policy of COVID-19 [125].