Since December 2019, the coronavirus disease 2019 (COVID-19) epidemic has incurred a significant health and economic burden worldwide. Even before severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was identified as its causal agent, COVID-19-related information was already spreading uninhibitedly over traditional and social media platforms at a strikingly rapid pace [1]. This phenomenon, called an “infodemic”—the over-abundance of information regarding an emerging event [2]—has been observed during prior public health emergencies [3–5]. During the COVID-19 pandemic, infodemics have reached unprecedented levels, and governments, and public health organizations around the world are now calling for measures to limit their effects [6].

Vietnam was one of the first countries that reported COVID-19 cases outside of mainland China. Very early into the epidemic, many interventions were put in place before any cases were reported, including border closures and travel restrictions, extensive case detection and contact tracing, and stringent quarantine measures. A series of public health interventions were gradually and promptly imposed to control the outbreak domestically [7], helping Vietnam to achieve 99 days without community transmission between April and late July 2020 (Figure 1). On July 25, 2020, a surge of unlinked COVID-19 cases without evidence of imported infection from abroad was spotted in Da Nang, a municipal city in Central Vietnam of high importance for foreign trade and tourism [8]. The outbreak affected mostly patients and staff linked to several hospitals, people in the community of Da Nang, and sporadic cases among people in other provinces with a travel history to Da Nang. Overall, more than 500 cases were reported in relation to this outbreak, with 495 (89.84%) in Da Nang, and 56 (10.16%) in 10 other provinces and cities across Vietnam. It was the first outbreak in Vietnam with COVID-19-related deaths since the beginning of the pandemic, with a total of 35 related fatalities. By the end of August 2020, the Da Nang outbreak was declared under control.

A series of public health measures were implemented by Vietnam government in response to this outbreak to limit and prevent further spread [7]. While some of these measures had already been introduced before the outbreak, the scope and enforcement were greatly intensified due to the urgency of this outbreak. To keep the public informed, information about these policies was frequently broadcasted by governmental agencies and various other outlets, including online platforms. Many of the estimated 69 million internet users in Vietnam (more than 73% of the population) use online media and user-generated online information as their main source of information about current events [9]. It is therefore important to recognize online information as a crucial means of communicating about health and risk during a COVID-19 outbreak, and to understand its capacity to impact public adherence to public health interventions.

Most online platforms do not fact-check user-generated online information, which creates an opportune environment for misinformation, defined in the field of public health as a “claim of fact that is currently false due to a lack of scientific evidence” [10], to spread widely with no curation or verification. The viral ability of misinformation becomes amplified by the rapidly reciprocating nature of internet, and misinformation is easily content-tailored for specific target audiences that are receptive to specific types of misinformation [11]. In addition, the interplay between sentiment and misinformation to spread certain agendas is a serious concern of researchers and policy-makers [12,13]. Existing evidence suggests that strong and polarized sentiments in online content play an important role in amplifying and driving the spread of misinformation [14,15]. Nonetheless, the sentiment profile of misinformation surrounding COVID-19 is still inconclusive. It has been recognized that online misinformation during the COVID-19 pandemic can create either a false sense of security or threat, and thus impact public health prevention and control efforts [16]. Existing evidence about online misinformation about COVID-19 is restricted to the evolution of the pandemic, conspiracy theories, or discriminative misinformation [17,18]. However, the infodemics surrounding specific public health interventions imposed by governments have not been studied. The World Health Organization recently published a research agenda to improve evidence-based tools, methods, and interventions for infodemics management [19]. This agenda highlighted the need to first measure and detect the spread and impact of misinformation in a localized context during the ongoing epidemic. In line with these priorities, we aimed to analyze the magnitude and sentiment dynamics of misinformation and unverified user-generated online information about five distinct public health interventions in response to the COVID-19 outbreak in Da Nang, Vietnam, between July and September 2020.

We found a low volume of misinformation and unverified information among online information about public health interventions during the Da Nang COVID-19 outbreak. Online posts containing unverified information and misinformation were more likely to have negative sentiments and contain a higher number of negative or positive words, and unverified information received higher engagement than other post categories.

Our study reported lower rates of misinformation than previous studies of COVID-19 or other recent epidemics [23,24]. This might be explained by the previous research of Gallotti et al. [25], who found a lower risk of infodemics in countries with stable political contexts and consistent public health interventions and messages throughout the epidemic. In 2020, Vietnam was regularly praised for its strict measures in response to COVID-19 and achieved one of the lowest COVID-19 infection and fatality rates globally. This success might have mitigated infodemic spread in Vietnam.

Many other studies on infodemics and misinformation in the COVID-19 context focused solely on Twitter [3,26]. Meanwhile, our study extended to all publicly available incountry online information, and beyond social media platforms, it included online newspapers and online forums, both of which are powerful information dissemination outlets in Vietnam. This thereby helped reflect online information flow outside the main international platforms that were used in previous research. Through this, we found that online forums and online newspapers were also a source of misinformation and unverified information. This highlights the gap in current research on COVID-19 misinformation, and also the need for infodemic control by public health agencies.

We found a strong relationship of misinformation and unverified information with sentiment polarity. This finding is in line with the study of Shahi et al. [27] on COVID-19 misinformation on Twitter, which showed that false claims featured more negative emotions than other news. In this study, more polarizing sentiments in misinformation were also closely related to the number of engagements of posts, which was also observed in previous studies on the number of retweets of COVID-19 information [28,29]. Our study showed that both unverified information and posts with negative sentiment received higher engagements than other posts. Similar conclusions were drawn from other studies on COVID-19, showing that negative information received more retweets [30]. Misinformation relies heavily on the implication of uncertainty and ambiguity of the situation, and it creates fear, anxiety, or negative emotions in readers through its content. This may also explain the observation of higher engagements for online information during the outbreak, the time that the general public might have perceived the most uncertainty towards the outbreak’s evolution, as well as the many measures implemented to contain it. Yet, this phenomenon of higher engagement for unverified information indicated that false or partially false information was more likely to spread and engage users. This implies not only the wide spread of misinformation, but also the danger of infodemics during times of uncertainty during the pandemic. Public health agencies, governments, and leaders should recognize this threat and strategize to effectively counter misinformation and unverified information, as the role of health education is crucial during pandemic times.

Our study was subject to several limitations. We did not explore in more detail the account characteristics or the semantics used, which would have given a more comprehensive depiction of not only the content of the posts, but also the entities that spread such information. We also limited our analysis to three sentiment statuses (positive, negative, or neutral). A more in-depth study on post sentiments might have captured more accurately the emotions underlying the generation of online information, and more importantly, misinformation. Thirdly, we selected only the 500 most influential posts among all collected posts due to limited resources for data processing. Forth, due to the nature of a retrospective study, the accurate rate of information in real time during the outbreak might not have been captured since some information might have been retracted or deleted. Moreover, our study was limited to only five distinct public health interventions over a short period of time, which might affect the generalizability of the findings. Nevertheless, we believe that, overall, our study offers a robust and valid analysis of an online infodemic related to a serious public health threat during the ongoing COVID-19 pandemic.

Our study provides important evidence about the volume and sentiment dynamics of misinformation and unverified information as part of the online infodemic during the ongoing COVID-19 pandemic. While the volume of incorrect or unverifiable online information was low overall, we showed that social media were not the only affected type of online platform. The choice of words, sentiment, and influence of the source had strong impacts on their distribution. This study offers important insights for public health decision-makers in Vietnam and other countries in the region with high rates of internet use to understand the public perceptions of health interventions in response to COVID-19.