Table 2. Summary of findings .

Review (disease and/or condition)	Summary of findings
Abbott et al. (SARS-CoV-2)19	• Overlap of published studies related to SARS-CoV-2 between 10 and 15 June 2020 (for example, 16 reviews addressed cerebrovascular-related comorbidities and COVID-19, as well as 13 reviews evaluating the broad topic related to chloroquine and hydroxychloroquine). • Despite the rapid pace to gather evidence during the pandemic, published studies were lacking in providing crucial methodological and reporting components (for instance, less than half of included studies critically appraised primary studies, only a fifth of included reviews had an information specialist involved in the study, and only a third registered a protocol). • Lack of transparent searching strategies and a lack of assessment and consideration of potential limitations and biases within the included primary studies limits the validity of any review and the generalizability of its findings. • The lack of prior registration of a review protocol was directly associated with poor quality of evidence. • Even though some reviews had been considered of low methodological quality, social media and academic circles highlighted these studies.
Alvarez-Galvez et al. (SARS, H1N1 and H7N9 influenza viruses, Ebola virus, Zika virus, Dengue virus, generic diseases, poliomyelitis)21	• The authors identified five determinants of infodemics: (i) information sources; (ii) online communities' structure and consensus; (iii) communication channels; (iv) message content; and (v) health emergency context. • Health misinformation can propagate through influencers, opinion leaders, or well-positioned individuals that may act as distractors or judges in specific social networks and certain philosophies and ideologies have higher impact on low health-literate individuals. • Misinformation is frequently derived from poor quality scientific knowledge. • Traditional media can contribute to the wrong interpretation of existing scientific evidence. • Opinion polarization and echo chamber effects can increase misinformation due to the homophily between social media users. For instance, considering Facebook and Twitter, people tend to spread both reliable and untrusting information to their networks. • Misleading health contents propagate and reverberate among closed online communities which ultimately reject expert recommendations and research evidence. • Although social media platforms offer opportunities for specialists to convey accurate information, they also offer other non-specialists opportunities to counter this with the spread of misinformation and exacerbating outrage. • Mass media can propagate poor-quality information during public health emergencies: it seems to be an ideal channel to spread anecdotal evidence, rumours, fake news and general misinformation on treatments and existing knowledge about health topics. • Included studies demonstrated that the number of high-quality platforms with health-related content is limited and these have several issues (e.g. language restriction and failure to publicize). • Alarmist, misleading, shorter messages and anecdotal evidence seem to have a stronger impact on the spread of misinformation.
Aruhomukama & Bulafu (SARS-CoV-2)29	• Forty per cent of included studies showed that nearly all of the respondents had heard about COVID-19, while only one included study stated that participants had inadequate knowledge of COVID-19. • Participants reported that social media and local television and radio stations were their major source of information with regards to COVID-19. • In two studies, participants confirmed that their family members and places of worship (churches and mosques) were the main information resource. • Authors also suggest the SARS-CoV-2 pandemic has not dramatically affected Africa due to high levels of knowledge, positive attitudes and perceptions and good practices for infection control. • Authors also suggest the need for health agencies to trail misinformation related to COVID-19 in real time, and to involve individuals, communities and societies at large to demystify misinformation.
Bhatt et al. (neurological, gastrointestinal, cardiovascular and urological diseases)30	• Based on included studies, there was a significant improvement in knowledge, awareness, compliance, and positive behaviour towards clinical practice guidelines with the use of social media dissemination compared to standard methods. • Included studies found that social media has a crucial role in rapid and global information exchange among medical providers, organizations and stakeholders in the medical field, and its power can be harnessed in the dissemination of evidence-based clinical practice guidelines that guide physicians in practice. • Methods for data dissemination varied from systematic tweets on clinical practice guidelines at regular intervals using a social media model, audio podcasts and videos on YouTube. Studies also found that the mixture of written text and visual images on social media with links to medical guidelines, multimedia marketing, and production company-led paid social media advertising campaigns also has great effect in improving knowledge. • The review did not find any standardized method of analysing the impact of social media on clinical practice guidelines dissemination as the methods of dissemination were highly variable.
Eckert et al. (disaster communication)23	• Each social media platform used for information streaming is beneficial during crisis communication for government agencies, implementing partners, first responders, and the public to create two-way conversations to exchange information, create situational awareness and facilitate delivery of care. • Social media mostly focused on spreading verified information and eliminating rumours via crowd-sourced peer rumour control, sometimes combined with quick and effective myth-busting messages by government officials. • Social media must be combined with other channels, especially with messages on traditional news media as they still have high credibility and were most often referenced on Twitter and social media. • Social media should be used by agencies, first responders and the public to monitor public reactions during a crisis, to address the public, create situational awareness, for citizen's peer-to-peer communication and aid, and to solicit responses from the ground (specifically of those individuals who are directly affected by a disaster). • Social media can also be effective during the preparation phase as it can train potentially vulnerable populations who would need to be evacuated. • Social media should be used to send and receive early warning messages during all phases of the disaster, to share information on the situation on the ground during onset and containment phases, and to inform friends, families and communities about aid, food, and evacuees during the containment phase. Twitter was suggested as a tool to map in real time the spread of floods and assess damage during a disaster.
Gabarron et al. (SARS-CoV-2)20	• Six of 22 studies that reported the proportion of misinformation related to SARS-CoV-2 showed that misinformation was presented on 0.2% (413/212 846) to 28.8% (194/673) of posts. • Eleven studies did not categorize the specific type of COVID-19-related misinformation, nine described specific misinformation myths and two categorized the misinformation as sarcasm or humour related to the disease. • Four studies examined the effect of misinformation (all reported that it led to fear and panic). One of the four reported that misallocation of resources and stress experienced by medical workers were also possible consequences of misinformation. • One study reported that approximately 46.8% (525/1122) of survey respondents were tired of COVID-19 being the main theme across all media. • Four studies mentioned increasing the health literacy of social media users. • These studies highlighted the need to educate social media users on how to determine what information is reliable and to encourage them to assume personal responsibility for not circulating false information.
Gunasekeran et al. (SARS-CoV-2 and COVID-19)31	• The exponential potential of social media for information dissemination has been strategically used for positive impact in the past. They can be applied to reinvigorate public health promotion efforts and raise awareness about diseases. • The epidemiological value of social media applications includes surveillance of information, disease syndromes and events (outbreak tracing, needs or shortages during disasters). • To draw attention to accurate information, social media seems to present a potential tool for governments to (i) rapidly assess public reaction to an outbreak, (ii) identify critical time points and topics that need to be addressed, and (iii) rapidly disseminate vital public health communication during outbreaks. • The review suggested that infoveillance (i.e. information surveillance) is the detection of events using web-based data, which can be faster than traditional surveillance methods. Earlier studies have successfully illustrated the use of microblogs and users’ geographical locations to track infectious disease outbreaks in many countries. • Although social media has the potential for positive public health utility, it can also amplify poor quality content. Public fear and anxiety are known to be heightened by sensational reporting in the media during outbreaks, a phenomenon heightened by the ease of sharing on social media. • Despite the negative impact of social media in propagating infodemics, it also provides a reservoir of user-generated content as individuals share a range of topics from emotions to symptoms. • Social media has also been applied as a tool for grassroots health promotion initiatives.
Lieneck et al. (SARS-CoV-2 and COVID-19)32	• One of the largest barriers to vaccine promotion through social media during the COVID-19 pandemic has been misinformation spread on social media. • Many sites such as Twitter and Facebook do not directly monitor these falsehoods which can be detrimental to the acceptance of the COVID-19 vaccine and putting a stop to the virus. • As vaccine hesitancy grows, social media can either be a tool to encourage greater protection via the COVID-19 vaccine or continue to fill knowledge gaps with misinformation preventing vaccination. • During the COVID-19 pandemic specifically, studies show that social media is contributing to the spread of misinformation about the vaccine, and that individuals who were hesitant about the vaccine were more likely to only use social media as their source of news. • Due to a lack of regulation of social media, a lot of vaccine scepticism can spread via such channels. This lack can particularly affect the COVID-19 vaccine acceptance rate among individuals. • As social media continues to rise in popularity, it has the potential to be an effective source of public health information that is accessible and up to date. • Social media platforms are increasing their efforts to reduce the amount of misinformation by limiting the untrue information and directing people to evidence-based websites. One potential strategy for controlling the spread of misinformation suggests the use of elaborated refutational messages, which can reduce misperceptions because they help people understand the flaws of misinformation.
Muhammed & Mathew (COVID-19, Australian Bushfire and the USA elections)33	• When a crisis occurs, affected communities often experience a lack of localized information needed for them to make emergency decisions. • Information overload and information dearth are the two concerns that interrupt the communication between the affected community and a rescue team. • Dread rumour looks more trustworthy and more likely to get viral. Dread rumour was the cause of violence against a minority group during COVID-19. • Political misinformation has been predominantly used to influence the voters. Misinformation spreads quickly among people who have similar ideologies. • Confirmation bias has a dominant role in social media misinformation related to politics. Readers are more likely to read and engage with the information that confirms their pre-existing beliefs and political affiliations and reject information that challenges it. • Health misinformation could delay proper treatment, which could further deteriorate patients’ health status and affect relevant outcomes, including mortality rate. • In the context of emergency situations (unforeseen circumstances), the credibility of social media information has often been questioned mostly by users, lawmakers, health professionals and the media. • The broadcasting power of social media and re-sharing of misinformation could weaken and slow down rescue operations. • Discourse on social media misinformation mitigation has resulted in prioritization of strategies such as early communication from the officials and use of scientific evidence. • Rumour correction models for social media platforms employ algorithms, mathematical simulations and crowdsourcing. • Studies on controlling misinformation in the public health context showed that the government could also seek the help of public health professionals to mitigate misinformation
Patel et al. (SARS-CoV-2)26	• The disinformation related to crisis communication about COVID-19 was focused on eroding trust in the government’s response and the accuracy of the official health messaging or misleading the public about accessing and receiving resources or support. • Decreased trust in governments and public health systems leads to disregard for the official health advice and impacts the population’s medical decision-making, often with serious detrimental effects. • The combination of actions to decrease trust in governments and health-related organizations are compounded in disadvantaged or vulnerable populations, such as those living in poverty, regions of conflict or in areas with poor infrastructure. The communication crisis faced during the COVID-19 pandemic can be attributed to a legacy of government mistreatment and a general lack of access to reliable information, which strengthens the impact of disinformation campaigns. • The malicious intent and execution of disinformation campaigns in Ukraine were intended to amplify and promote discord to create a political impact in Ukraine, particularly in the context of the ongoing war. • Disinformation instigated the physical interruption of access to health care.
Pian et al. (COVID-19)34	• Social media use and low level of health and/or eHealth literacy were identified as the major causes of the infodemic. • There is a pattern of spiral-like interactions between rumour-spreading and psychological issues. Integrating psychological variables with models of rumour-sharing behaviour might be beneficial. • Multidisciplinary empirical studies should be conducted to validate the effectiveness of countermeasures applied to multiple groups (such as low level of health/eHealth literacy, social media/mass media platforms, governments, and organizations). Even if the countermeasures seem logical, how effective they are when applied in different contexts (e.g. different geographical regions, user profile, social media platform, etc.) need to be investigated. • One of the major causes of the infodemic is social media use, although social media can play a positive or negative role. • The rapid publication of editorials, commentaries, viewpoints and perspectives are also mentioned by the authors of the review to be the major cause of the infodemic, due to its low level of certainty and evidence. • Negative impacts were identified and related to the infodemic, including public psychological issues, breakdown of trust, inappropriate protective measures, panic purchase and the global economy. • The authors proposed various countermeasures against the COVID-19 infodemic, which were grouped into the following categories: countermeasure strategies for a low level of health and/ or eHealth literacy, social media/mass media platforms, governments, and organizations, risk communication and health information needs and seeking.
Rocha et al. (COVID-19)35	• Infodemic can cause psychological disorders and panic, fear, depression and fatigue. • Many occurrences were false news masquerading as reliable disease prevention and control strategies, which created an overload of misinformation. • Different age groups interact differently with the fake news propagated by social media. A specific focus should be given to people older than 65 years as they usually have limited skills managing social media systems. • Social media has contributed to the spread of false news and conspiracy theories during the COVID-19 pandemic. • Infodemic is part of people’s lives around the world, causing distrust in governments, researchers and health professionals, which can directly impact people’s lives and health. • During the COVID-19 pandemic, the disposition to spread incorrect information or rumours is directly related to the development of anxiety in populations of different ages.
Suarez-Lledo & Alvarez-Galvez (vaccines, smoking, drugs, noncommunicable diseases, COVID-19, diet and eating disorders)24	• Health topics were ubiquitous on all social media platforms included in the study. However, the health misinformation proportion for each topic varied depending on platform characteristics. • The proportion of health misinformation posts was dependent on the topic: vaccines (32%; 22/69), drugs or smoking issues (22%; 16/69),a noncommunicable diseases (19%; 13/69), pandemics (10%; 7/69), eating disorders (9%; 6/69) and medical treatments (7%; 5/69). • Twitter was the most used source for work on vaccines (14%; 10/69), drugs or smoking products (14%; 10/69), pandemics (10%; 7/69) and eating disorders (4%; 3/69). For studies on noncommunicable diseases (13%; 9/69) or treatments (7%; 5/69), YouTube was the most used social media platform. • Health misinformation was most common in studies related to smoking products, such as hookah and water pipes, e-cigarettes and drugs, such as opioids and marijuana. • Health misinformation about vaccines was also very common. Therefore, the potential effect on population health was ambivalent, that is, both positive and negative effects were found depending on the topic and on the group of health information seekers. • Authors identified social media platforms as a potential source of illegal promotion of the sale of controlled substances directly to consumers. • Misleading videos promoted cures for diabetes, negated scientific arguments or provided treatments with no scientific basis. • Although social media was described as a forum for sharing health-related knowledge, these tools are also recognized by researchers and health professionals as a source of misinformation that needs to be controlled by health experts.
Tang et al. (H1N1 and H7N9 influenza viruses, Ebola virus, West Nile virus, measles, MERS-CoV and enterohaemorrhagic Escherichia coli)25	• In general, approximately 65% (225/344) of videos contained useful information (either accurate medical information or outbreak updates) across different emerging infectious diseases, while the rest of videos contained inaccurate or misleading information. Whether misleading videos had a significantly higher number of views per day is unclear. • Independent users were more likely to post misleading videos and news agencies were more likely to post useful videos.
Truong et al. (vaccination, H1N1 and Ebola)27	• Lack of information and misinformation about vaccination against H1N1 influenced participants’ decision to vaccinate. • Lacking adequate information surrounding vaccination against H1N1 or encountering contradictory information from different sources can reduce an individual’s willingness to vaccinate. The lack of accurate information associated with vaccines would affect the population’s willingness to vaccinate against other infectious diseases (such as Ebola). • Although the internet can be a useful resource to spread vital public health information during a pandemic, a lack of clarity and consistency of information may deter people from vaccination. • People that do not have a comprehensive understanding of how vaccines work are unable to make informed and confident decisions about vaccination. Therefore, communicating information regarding vaccination in a clear and accessible manner to better educate people and overcome barriers to vaccination is essential.
Walter et al. (countermeasures against misinformation)22	• The meta-analysis showed that source of misinformation emerged as a significant moderator (P-value: 0.001). Specifically, correcting misinformation is more challenging when it is delivered by our peers (d = 0.24; 95% CI: 0.11–0.36) as opposed to news agencies (d = 0.48; 95% CI: 0.15–0.81). • The source of the correction played a significant role (P-value: 0.031), resulting in stronger effects when corrective messages were delivered by experts (d = 0.42; 95% CI: 0.28–0.55) compared with non-experts (d = 0.24; 95% CI: 0.13–0.34). • There was no significant difference (P-value: 0.787) between interventions that employed Facebook rather than Twitter. • Finally, the results suggest that it is more difficult to correct misinformation in the context of infectious disease (d = 0.28; 95% CI: 0.17–0.39) as opposed to other health-related issues (d = 0.55; 95% CI: 0.31–0.79). • The effects of myths about genetically modified produce, nutrition and reproductive health were more effectively attenuated by corrective interventions than misinformation about Zika virus, measles, HIV and other communicable diseases.
Wang et al. (vaccination, Ebola virus and Zika virus, along with other conditions and topics, including nutrition, cancer and smoking)28	• Misinformation is abundant on the internet and is often more popular than accurate information. • Most commonly health-related topics associated with misinformation are communicable diseases (30 studies), including vaccination in general (eight studies) and specifically against human papillomavirus (three studies), measles, mumps and rubella (two studies) and influenza (one study), as well as infections with Zika virus (nine studies), Ebola virus (four studies), MERS-CoV (one study) and West Nile virus (one study). • Misconceptions about measles, mumps and rubella vaccine and autism, in particular, remain prevalent on social media. • Other topics share scientific uncertainty, with the authorities unable to provide confident explanations or advice, as with newly emerging virus infections such as Ebola and Zika viruses.

CI: confidence interval; COVID-19: coronavirus disease 2019; H1N1: influenza A virus subtype H1N1; H7N9: Asian lineage avian influenza A H7N9; HIV: human immunodeficiency virus; MERS-CoV: Middle East respiratory syndrome coronavirus; SARS: severe acute respiratory syndrome; SARS-CoV-2: severe acute respiratory syndrome coronavirus 2.

^a Numbers are reported as given in original publication despite that the percentage is inconsistent with numerator and denominator.