With 340 million registered users, 166 million daily active users, and 500 million tweets per day , Twitter constitutes one of the world’s most widespread communication platforms, especially in a public health crisis. Although social media can help with rapid knowledge dissemination in a pandemic , no media is a passive vehicle for communication. Like on other social media platforms, where concise, emotive and immersive content spreads like fire, we have seen Twitter become a “fertile ground for the spread of false information, particularly regarding the ongoing coronavirus disease” . Recognising its role in misinformation propagation, in March 2020, Twitter introduced warning labels for tweets containing potentially harmful or misleading information relating to Covid-19 and linked verified information .
Nonetheless, Twitter has played a pivotal part in health risk communication during the Covid-19 health crisis [33,34,35]. Various world leaders have utilised the platform to inform, boost morale and prompt political discussion . Given such uptake, it is not surprising that health measures trended in the Twittersphere [37,38,39]. This study documents several health risk measures communicated, often in combination. Most frequently were the measures ‘stay home’ and ‘wear a mask’ — messages focused on actions at the individual level. Concerning the latter, it should be noted that throughout 2020 the WHO iteratively updated their recommendations about mask wearing and even ran social media challenges, such as the #WearAMask and #StayHealthyAtHomes challenges. These updates and efforts could have contributed to the popularity of this topic in the tweets analysed.
Messages targeting individual agency and responsibility for controlling health raise the ethical issue of culpability [40, 41]. As Guttman explains , messages that appeal to personal responsibility have pervaded public health communications for decades and can have unintended adverse effects. For example, the tweets shaming citizens for not complying by staying home or wearing a mask could have prompted feelings in non-abiders of guilt, shame or frustration. However, these individuals may not have had a choice, needing to go work to support their family, or not being able to wear a mask for health reasons.
Ethical consideration must also be given to the message framing, specifically regarding the potential for persuasive and paternalistic communication styles, which can create a barrier and lead to erosion of trust. On the other hand, more educational approaches provide only information to enhance rational decision-making, but research shows they are not always effective . In this study, most tweets used health loss or gain framing to persuade adherence to public health measures. Meaning, they presented Covid-19 preventative measures by emphasising their health-protective capacities, or the negative consequences resulting from non-adherence. Out of these two, ‘health gain’ messages spread more (calculated by retweets divided by a user’s number of followers), but ‘health loss’ was the most frequent (in terms of number of tweets in our sample). Appeals to fear using vivid images or describing damages to health echoes earlier public health campaigns, such as smoking or HIV. This approach came under ethical critique for causing unnecessary fear and stigmatisation .
However, a public health crisis may justify negative emotional appeals or paternalistic communication strategies to ensure maximal adherence and societal safety [42, 43]. Indeed, prospect theory proposes that loss-framed messages have more success when outcomes are riskier and more uncertain (like in a pandemic with high infectious rates and unclear solutions), while gain-framed messages are more persuasive when outcomes are clearer and more apparent [24, 44,45,46]. In the Twittersphere, “fear for the unknown nature of the coronavirus” underscored most Covid-19 conversations . This ethical crossroads should be approached with great discretion.
The study results also show that the most retweeted Covid-19 risk communication with visuals took the format of photographs, often with logos and text. One possible reason for this predominance of photos is that they have evidential power by documenting reality. Studies on the role of photographic images also emphasise their multiple roles, including dramatizing experience to increase communicative impact . In other words, they have emotive and rhetorical power and provide easy and quick content for viewers to digest [48,49,50]. In the context of health communication, research shows visual aids and animated graphics positively influence attention, comprehension, recall and behavioural adherence [51, 52].
Despite the potential of photographs in health communication, some question using their vividness and strong emotional appeal (as common persuasive marketing tactics) to attract attention and convey information about risk . An overtly aesthetic or dramatic approach can force the audience’s attention to particular messages or content to persuade them. However, this may have unintended impacts. For instance, one of the analysed tweets included a video of a conventionally attractive young woman wearing tight clothing and handing out masks to men. Although this video tailored to male viewers successfully drew attention to mask-wearing, it also reinforced negative stereotypes and societal gender/power imbalances.
Still, images transcend literacy and language requirements and so can help promote understanding, accessibility and fairness . Notably, the use of images alongside text is most effective, as was the case in most tweets (68%) in this study. Indeed, combining visual and linguistic signification increases health communication effectiveness . Ultimately, when sensitive to ethical concerns, visual aids can be “among the most highly effective, transparent, fast, memorable, and ethically desirable means of risk communication” .
Our analysis of the tweet sources also provides insight into the role of governments and media outlets’ in sharing visual health risk communication on Twitter. Concerning the former, research has shown that a higher intensity of government communication via social media positively influences citizens’ adherence to preventive measures . Previous crisis-related research indicates that health organisations rely more often on traditional media than social media when framing a health crisis [56, 57]. In the context of Covid-19, recent research shows that the tweets of politicians generated the most attention, while those of celebrities attracted the most engagement overall, thereby indicating the value of personal versus official communication channels . Our study results echo this, revealing that individual voices (‘influencers’ with many followers) predominated and had their tweets had the highest spread.
However, health/government institutions and the media also had a significant presence but only at the start. As Fig. 5 illustrates, at the onset of the pandemic, most tweets came from the media (indicated by blue) and health and government organisations (indicated by pink). These stakeholders’ tweets then tapered out into an even distribution. This pattern could reflect citizens’ desire for official guidance at the outset of the pandemic when everything was in a state of uncertainty. The shift towards individual voices from March onwards aligns with the stay-at-home mandates when individual social media use generally increased . The prominence of individual voices highlights the importance of citizens (particularly influencers) sharing health messages among their networks, enabling health messages to reach broader segments of the population and promoting solidarity and inclusiveness.
Finally, the high number of tweets with tones of critique shows how Twitter, even in the context of health-risk communication, gets used as a platform for communicating protest. In September and October, the spikes in critical tweets in our sample came from US tweets, often with political undertones (unsurprising in the lead up to the US election), alongside Indian students protesting against exams. For the latter, authorities were allowing exams despite social distancing and staying home being officially recommended to prevent infections and the spread of Covid-19 . Since the Arab Spring and Occupy Wall Street movements, Twitter has developed a reputation as a platform for protests because it amplifies individual voices, and the mass of critical tweets in this study reflects this. That most tweets used photographs also fits as photos can help build social movements and networks [60, 61], visuals fortify propaganda during conflicts  and images can foster advocacy, as we have also seen with climate change movements [63, 64]. Ultimately, this highlights how critical tones about potential damages to health ignite activity on Twitter and that citizens play a crucial role in information distribution.
This study has some limitations. To start, we recognise that filtering for only the top 500 Covid-19 tweets in English per month means the exclusion of other potentially relevant tweets. Moreover, when interpreting our findings, it is important to consider that our analysis presents a snapshot of the retweet counts (as retweet and follower counts were collected at two points in time) and does not account for the potential impact of country-specific events. As well, due to Twitter’s collection limit (a 1% threshold of the entire tweet-volume on Twitter at a given moment) for a short period between mid-March and mid-April the collection using Crowdbreaks was limited to a random subsample of all tweets of interest. However, given the volume of tweets collected the sample is representative and suitable to answer the research questions. This approach’s strength was that it thus revealed the extent to which preventative measures appeared amongst the tweets with the most retweets. However, by only including English language tweets, this study’s results may not reflect global trends as they are biased towards the West. As well, duplicate images were not documented. Another limitation lies in the fact that we limited our analysis to tweets promoting WHO preventative behaviours; this may have led us to miss other types of preventive messages. However, we deemed this a reasonable strategy for verifying the legitimacy and effectiveness of preventive behaviours being promoted on Twitter, as was the study’s focus. Further, although all tweets analysed in this study came from verified accounts, it was beyond this study’s scope to verify Tweet locations’ accuracy and to identify the potential presence of bots.