Technology advancements have offered new opportunities for numerous sectors, allowing them to develop and enhance quality, with the healthcare industry benefiting from digital transformation by improving patient care, safety, and capacities [11]. Researchers have turned their focus to COVID-19 and aimed to determine and analyze the echo of the COVID-19 around the world, the public attitude towards the coronavirus vaccine, the perception of the parents about their children in this period, and the attitude of the parents towards a possible vaccine to be given to their children. Thus, they carried out their research by adopting many different data sources, methods, and perspectives. It was established that studies conducted in the early days of the pandemic were focused directly on the epidemic and also discussed policymakers' actions around the world or in a specific country. On contrary, it was observed that the scope of the subject was expanded in the future, and different perspectives were included in the studies conducted.
2.1 COVID-19 echo and vaccine perception in the world
COVID-19 has completely changed the lifestyle of people in different regions and countries; thus, it has become a very important global problem. Coronavirus vaccines have attracted great interest from the public, subsequently, they have led to many discussions that have brought about concerns and hesitations. In this context, the researchers, who emphasized the importance of understanding the repercussion of COVID-19 in the public, have set themselves the goal of examining the troubles experienced by public and parents during the pandemic also, the effects of these troubles on children, as well as analyzing the concerns of families for their children. In this way, they aimed to guide policymakers by examining the problems and concerns for increasing vaccine intention and shed light on the debates about vaccines.
Patrick et al. [12], Zhen [13], Yeasmin et al. [14], Lazarus et al. [15] conducted a research study by using questionnaire to understand parents' perceptions of the consequences for their children and families during the epidemic. Murphy et al. [16], Alfieri et al. [17], Yigit et al. [18], Halvorson et al. [19], Bell et al. [20] carried out a study with the help of surveys, emphasizing that identifying vaccine hesitancy in different samples for children’s and general public.
With the help of online surveys, Ali et al. [21], Fitzpatrick K et al. [22] aimed to analyze the behavior, knowledge, and perceptions of the public regarding the epidemic to identify deficiencies in key parts of public information. Khubchandani et al. [23], Ward et al. [24], Reiter et al. [25], Malik et al. [26], Zhang et al. [27], Skjefte et al. [28], Yılmaz and Sahin [29] took help from social media to get ideas from the general population and conducted online surveys for the vaccine perceptions.
Singh et al. [30], Raamkumar et al. [31], Park et al. [32] aimed to develop a perspective on the pandemic by addressing social media platforms like Twitter, Facebook. Scannell et al. [33], wanted to figure out how different persuasive strategies were employed in COVID-19 vaccination tweets. Also, Jenkins and Moreno [34] aimed to analyze the shares of parents on social media about getting their children vaccinated.
In order to analyze the public's thoughts and discourses about the epidemic, support is often received from online environments. In addition, the traditional method of surveys was carried out from online platforms to find out what the general public thinks, thus, the opinions of the public are taken into consideration transparently. Also, to analyze the perception of vaccines, researchers aimed to determine the existing attitudes by asking specific questions about the vaccine. As a result of surveys or interviews with parents, it was discovered that the COVID-19 showed some results in terms of education and physical/mental health in children. When looking at existing studies, it was shown that relatively few uses major social media platforms other than blogs to profit from machine learning approaches, as a result, the lack of this situation in the literature has been observed. It is thought that conducting a study on the hesitancy of vaccination in children on Twitter, where the public shares their feelings in the most transparent way, will bring clarity to the subject and bring the issue of children and vaccination to the fore with sharp lines throughout the world.
2.2 Natural language processing (NLP) studies in the COVID-19
Natural language processing (NLP) is a field that tries to process, understand, and interpret human language. It provides methods that help transform the text into a structured representation and enables artificial intelligence to make sense of it by taking human language as input. In short, they are techniques that enable automatic extraction and identification of information from texts [35]–[37]. In this context, to analyze the attitudes of the public against the pandemic, researchers have benefited from NLP techniques and examined the main themes and mood changes of public perception within the historical frameworks they determined.
To develop an answering framework to answer medical questions Masum et al. [38] were used the methods of query expansion, data pre-processing and vector space models. Also, Klein et al. [39] was applied the deep neural network classifier based on Bidirectional Encoder Representations from Transformers (BERT) model for Developing a Twitter-based NLP data pipeline. For coping with misinformation during the outbreak, Ayoub et al. [40], were put a framework by getting help from the SHAP and DistilBERT methods. Latent semantic analysis (LSA) was performed for extracting keywords based on demographic, social, epidemiological, economic, psychological, medical, and clinical perspectives of the pandemic with the support of NLP algorithms, based on the literature by Bose et al. [41]. And also, Tang et al. [42] showed the application of BERT for analyzing the tweets about the epidemic posted by health organizations.
Sadman et al. [43] collected news reports about the pandemic and used NLP techniques to obtain information about the number of cases, trending topics, emotions, and the virus. L. Li et al. [10] received support from NLP techniques by processing the data pulled from the Weibo platform with the help of supervised learning to classify the available information about the epidemic into different types of situation information. On the other hand, Samuel et al. [44] aimed to determine the public perception of COVID-19, with the help of sentiment analysis packages of the R program, by analyzing tweets about the pandemic. Osakwe et al. [45] aimed to identify the main issues by using textual data to determine the reaction and concern of the public during the pandemic, with the support of tweets .
Different NLP techniques are used by researchers to evaluate public opinions with the support of social media platforms, to determine the accuracy of information shared by news sources or websites, to determine how much the public trusts the news, information, or ideas that are circulating, and how such articles affect people has been observed. Topic modeling techniques have come to the fore, as researchers who perform unsupervised learning practice mostly use the. Furthermore, it was discovered that the authors made extensive use of sentiment analysis techniques to further strengthen their research and determine the perception of public opinion, by this means, they had the chance to understand, also, interpret the public's feelings about the pandemic.
2.2.1 Topic modeling and sentiment analysis studies on the perception of COVID-19
Topic modeling, also known as probabilistic clustering, is thought to be one of the most effective techniques for classifying and clustering textual data [46], [47]. Researchers prefer to use topic modeling techniques that make use of unsupervised learning to reveal hidden thematic structures from the data sets they have. Also, Sentiment analysis is a computer tool of NLP that researchers use to identify the public's point of view on a topic [48]. With the use of sentiment analysis, people's emotions can be interpreted and the interpreted emotions can be used where necessary for any organization [49], [50]. Techniques related to this aspect have played a key part in the studies carried out to inform policymakers and understand the emotional change-development of the public in the COVID-19 by attracting the attention of researchers.
By using topic modelling, Agarwal et al. [51] developed a system for analyzing tweets about the COVID-19. On the other hand, Doogan et al. [52] identified the posts about non-drug interventions by considering six different countries. Also, Gozzi et al. [46] focused on the public's internet response and media content during the pandemic. Liu et al. [54] compared people's behavior changes, thoughts, confirmed cases, and deaths. Examining media reports about the outbreak and health communication patterns governed by the media Q. Liu et al. [55] determined 9 main themes.
Tsai and Wang [48] aimed to perform a sentiment analysis study with the help of Twitter data, and also, examined the relationship between mood changes in tweets about the pandemic and public health policies. Lwin et al. [56] aimed to analyze the worldwide emotional trends based on four main emotions, namely anger, fear, joy, and sadness, as well as to investigate the underlying causes of the emerging emotions in this direction. Pokharel [57] aimed to conduct a sentiment analysis to determine how people living in different countries coped with the pandemic situation based on 12 selected countries of the tweets sent. According to the tweets shared on Twitter, Dubey [58] aimed to analyze emotions and feelings, as well as to investigate the situation of cyber racism that increased during the epidemic. In order to ascertain the mental state of a people during their health period, Singh et al. [59], who received support from Twitter, performed a sentiment analysis with the help of the BERT model, by performing an application on tweets sent by users. Samuel et al. [44] tried to detect public awareness of the epidemic by using tweets.
Aware of the advantageous aspects of topic modeling and sentiment analysis methods, the researchers thought that using these two techniques could be more efficient in listening to the voice of the public and observing the process. For example, to raise public awareness of the epidemic and revealing issues of concern shared by social media users Boon-Itt and Skunkan [60] were applied these two methods. Yin et al. [61] present a new framework to analyze the emotional dynamics and topics about the epidemic from social media posts. Chen et al. [62] used Twitter to learn about the public's opinion of the pandemic. Hung et al. [63] analyzed and identified sentiments related to the pandemic on Twitter. Also, Abd-Alrazaq et al. [64] defined the main topics shared by Twitter users about the pandemic.
Ebadi et al. [65] aimed to identify hidden issues by examining publication similarities and the change of emotions by using a structural topic modeling framework. Oyebode et al. [66], by using six different social media platforms, aimed to analyze the public's thoughts and comments regarding the COVID-19. Li et al. [67] aimed to examine the tweets of the COVID-19 period in terms of mental health by developing models. After the curfews, Hanschmidt and Kersting [68] aimed to analyze the emotions of the public reflected on social media platforms and to examine the connection with emotions by revealing the main themes discussed. Raju et al. [69] aimed to put forward an NLP model with high classification accuracy based on the BERT model, which will support taking urgent measures to stop the proliferation of the epidemic by cleaning the misinformation on social media for health institutions. Lee [70] aimed to determine the topics around which people's thoughts were shared on Twitter about COVID-19, why these issues came to the fore, and how emotions developed during the epidemic. Vydra and Kantorowicz [71] aimed to determine how useful social media data are for policymakers using latent semantic scaling and structural topic models. Focusing on different periods, M. S. Ahmed et al. [72] aimed to examine the sentiment of users and support trending topics using a dataset of tweets about the epidemic. Fazeli et al. [73] conducted a study when the epidemic first emerged, aiming to present a framework and present a multi-faceted analysis of the critical features reflected by the conversations on social media.
It was observed that the researchers, by pulling the main themes of the epidemic in news, articles, or tweets, divided the perceptions into different clusters, and analyzed what perspectives were formed in the public. According to the research, Latent Dirichlet Allocation (LDA), which is one of the most effective algorithms in technically unsupervised machine learning applications, is frequently utilized as a data source to obtain public information. Researchers, focusing on understanding the psychological impact of the pandemic on people, thought that the best way for this was sentiment analysis, and focused on analyzing perceptions related to the epidemic by making use of different methods. With the help of two NLP techniques, more comprehensive results were revealed, and both main themes and emotions were determined with sharp lines. At this point, the striking point is that social media platforms are predominantly preferred in studies, and it has been determined that Twitter is the most used social media platform to obtain clearer data. As a consequence, it has been observed that these two techniques are used separately in the articles, to the best of our knowledge, there hasn't been any research that combines these two methods and puts forward a model.
2.2.2 COVID-19 vaccine perception with topic modeling and sentiment analysis
Researchers aimed to reveal the attitudes of the public toward COVID-19 vaccines, which are thought to be a way to prevent COVID-19. In addition, they aimed to present studies that approached the event thematically and determined the views of the society to understand people's perspectives on both a possible vaccine and the current vaccine, in this way, they benefited from topic modeling techniques. Managers and health policymakers used evidence-based scientific data to guide decision-making [74], [75] [76]. Focusing on analyzing and classifying text emotions, sentiment analysis can describe people's perspectives on public health policies for policymakers [48]. In this way, subjective opinions can be categorized within themselves and gain meaning. With this respect, sentiment analysis techniques attract the attention of the authors and have been widely used in examining the public acceptance of vaccines produced or being developed for the coronavirus. The authors, who want to take the advantageous aspects of the topic modeling and sentiment analysis methods under the umbrella of NLP, received support from these techniques to determine the attitudes about the recently popular COVID-19 vaccine. In this way, they have introduced models to the literature that extract key themes and sentiments about vaccines.
To uncover themes found in the public's thinking about possible vaccines early in the COVID-19 Jiang et al. [77], to observe temporal changes by uncovering themes in tweets S. Liu et al. [54], to analyse comments on social media about parents, children, vaccines, and COVID-19 Thurson [78] used LDA method. Also by applying sentiment analysis, Ahmed et al. [49] analyzed public opinion about the COVID-19 vaccine, Sattar and Arifuzzaman [79] determined vaccine insights and examining the public's perspective on safety measures after intake and Hussain et al. [4] developed an artificial intelligence-based model. Gbashi et al. [80] performed systematic review for vaccine opinion.
To be able to identify the main themes and feelings discussed the vaccine Lyu et al. [81] used topic modelling and sentiment analaysis methods together. Additionally, to deduct topics and feelings about the vaccine Kwok et al. [82] put forward a model. Shim et al. [1] analyzed, interpreting, and classifying tweets about the vaccine. Karami et al. [83] determined the sentiment of tweets, pinpointing key issues, examining change, and revealing key points.
In topic modeling studies, it has been observed that Twitter is generally used to pay attention to the voice of the public by using the LDA method, but besides Twitter, blogs, articles, and news sites are examined. The authors identified the main themes, made recommendations to policymakers, and examined the public's thoughts, confidence, and discourses against vaccination. In order to analyze the mood of the people against the vaccines to be made to prevent the epidemic, the authors benefited from different sentiment analysis techniques. It has been emphasized that states and policymakers should be more transparent and clearer to the public about the vaccine to prevent these concerns.
While the authors aimed to identify the main topics and feelings from the ideas, and discourses of the public using vaccine-related keywords, they preferred social media, especially Twitter. It has been observed that researchers mostly benefit from LDA, which is one of the unsupervised learning techniques of topic modelling. It was found that control measures against the vaccine were generally supported, and false information was rejected. Conspiracy theories have created a shield against the vaccination even though it has been noticed that positive emotions are not enough to reach the amount of vaccine needed to achieve herd immunity. It was emphasized to governments that they should pay attention to the people's voices, and also, be pioneers in supporting vaccine development and clinical management by creating a vaccine promotion plan.