Sentiment, Contents, and Retweets: A Study of Two Vaccine-Related Twitter Datasets

Health Communication, Social Media, vaccines

 

Elizabeth B Blankenship, MPH; Mary Elizabeth Goff, MPH;
Jingjing Yin, PhD; Zion Tsz Ho Tse, PhD;
King-Wa Fu, PhD; Hai Liang, PhD; Nitin Saroha, MS;
Isaac Chun-Hai Fung, PhD

Perm J 2018;22:17-138 [Full Citation]

https://doi.org/10.7812/TPP/17-138
E-pub: 06/11/2018

ABSTRACT

Introduction: Social media platforms are important channels through which health education about the utility and safety of vaccination is conducted.
Objective: To investigate if tweets with different sentiments toward vaccination and different contents attract different levels of Twitter users’ engagement (retweets).
Methods: A stratified random sample (N = 1425) of 142,891 #vaccine tweets (February 4, 2010, to November 10, 2016) was manually coded. All 201 tweets with 100 or more retweets from 194,259 #vaccineswork tweets (January 1, 2014, to April 30, 2015) were manually coded. Regression models were applied to identify factors associated with retweet frequency.
Results: Among #vaccine tweets, provaccine tweets (adjusted prevalence ratio = 1.5836, 95% confidence interval = 1.2130-2.0713, p < 0.001) and antivaccine tweets (adjusted prevalence ratio = 4.1280, 95% confidence interval = 3.1183-5.4901, p < 0.001) had more retweets than neutral tweets. No significant differences occurred in retweet frequency for content categories among antivaccine tweets. Among 411 links in provaccine tweets, Twitter (53; 12.9%), content curator Trap.it (14; 3.4%), and the Centers for Disease Control and Prevention (8; 1.9%) ranked as the top 3 domains. Among 325 links in antivaccine tweets, social media links were common: Twitter (44; 14.9%), YouTube (25; 8.4%), and Facebook (10; 3.4%). Among highly retweeted #vaccineswork tweets, the most common theme was childhood vaccinations (40%; 81/201); 21% mentioned global vaccination improvement/efforts (42/201); 29% mentioned vaccines can prevent outbreaks and deaths (58/201).
Conclusion: Engaging social media key opinion leaders to facilitate health education about vaccination in their tweets may allow reaching a wider audience online.

INTRODUCTION

Communicating the benefits of vaccination to the public remains a challenge amid the presence of the antivaccination movement.1 This movement causes hesitance and criticism among parents regarding vaccines for myriad reasons, including lack of trust in government and the pharmaceutical industry, feared acute and long-term side effects, and concern over the chemical makeup of the vaccines themselves.2,3 Outbreaks of vaccine-preventable diseases in the US occur more often as rates of vaccination decline. For example, measles had been eliminated in the US since 2000 until travel-related imported cases led to outbreaks in recent years, including a large outbreak among unvaccinated Amish individuals in 2014.4 

Social media has become a major mode of global communication, through which dissemination of information is easier than ever. Currently, 21% of all US adults use Twitter, with 42% of those users visiting the Twitter platform daily.5 With more than 328 million users,6 Twitter is a convenient tool for discussing public health topics, including vaccination. Both provaccine and antivaccine information is prevalent on Twitter. Understanding how vaccine-related information disseminates on Twitter is vital, especially because a minority of users are openly skeptical about vaccines and advocate against vaccination. Prior research focused on how vaccines were portrayed on social media7,8 and how misinformation or controversial information spread.9-11 Researchers attempted to develop methods to monitor vaccination sentiment in real time by primarily focusing on the incidence of tweets with positive and negative sentiments over time.5,12 Efforts were made to use supervised machine learning methods to predict a tweet’s sentiment toward vaccination, using either contents of manually coded tweets or their users’ connections as classifiers.13,14 Although important progress has been made, questions remain at the microlevel, such as whether tweets containing provaccine or antivaccine sentiment and information attract attention on Twitter.

Here, we provide definitions to a few Twitter-specific terms. Retweets are tweets that users repost after reading them in their timeline.15 A Twitter user’s follower count is the number of Twitter users who follow the account of a user. A Twitter user’s friend count is the number of Twitter users whom the user follows on Twitter. A Twitter user’s status count is the number of status updates (tweets) that the user has posted so far. A Twitter user’s favorite count is the number of likes the user has ever given to other people’s tweets.

In this article, we report analyses of two distinct datasets that, in turn, addressed four interrelated research questions.

Study A: #vaccine Twitter Dataset

In Study A, we analyzed a 1% stratified random sample of a corpus of tweets with the hashtag #vaccine, a hashtag used by both provaccine and antivaccine advocates. We believed that tweets carrying stronger sentiments would attract more attention and retweets from those who wanted to share them. Therefore, we hypothesized as follows:

Hypothesis 1: Antivaccine and provaccine #vaccine tweets differ in their retweet count, compared with tweets of neutral sentiment.

We also postulated that users’ characteristics could be potential confounders in the association between sentiment and retweet frequency, and therefore we included the users’ follower count, friend count, status count, and favorite count in our analysis.

We also speculated whether different categories of antivaccine contents attracted different quantities of retweets.

Hypothesis 2: Different categories of contents among antivaccine #vaccine tweets differ in their retweet count.

We were also interested in the source of information in the provaccine and antivaccine #vaccine tweets.

Research Question 1: What were the embedded Uniform Resource Locator (URL) domains in the provaccine and antivaccine #vaccine tweets?

Study B: #vaccineswork Twitter Dataset

In Study B, we analyzed a corpus of tweets with the hashtag #vaccineswork. This hashtag has been used by public health professionals when they promoted vaccination.16 Because the distribution of retweet count is highly skewed with only very few tweets having high retweet count, it is likely that tweets with high retweet counts are read by many and may have influence over the knowledge, attitudes, or perceptions of many users, whereas tweets with few retweets do not. Given the need to perform manual coding, in Study B, we chose to focus our limited resources on tweets that carry the greatest influence rather than tweets with minimal influence. We manually categorized the contents of tweets containing #vaccineswork that were retweeted 100 or more times. We provided a descriptive analysis of the distribution of topics among this sample of highly retweeted tweets. We also combined several topics into a categorical variable and tested if statistical association existed between retweet frequency and that categorical content variable.

Research Question 2: Would highly retweeted provaccine contents on Twitter (#vaccineswork tweets) differ by content in their retweet frequency?

METHODS

This research was approved by the institutional review board of Georgia Southern University (H15083) under the B2 exempt category because the social media posts analyzed in this study are considered publicly observable behavior.

Study A: #vaccine Twitter Dataset

Data

The #vaccine dataset was retrieved using Twitter Application Programming Interface (API; Online Supplementary Materialsa). The data contain 142,891 tweets from Twitter with the hashtag #vaccine, from February 4, 2010, to November 10, 2016 (inclusive). Retweet frequency and other meta-data reported in this paper were correct as of the data retrieval date (November 10, 2016). Data were then stratified by month, and a random 1% sample of tweets was collected from each month, resulting in the extraction of 1425 tweets for manual coding.

Manual Coding

Authors MEG and EBB previewed tweets for recurring themes within the content of the tweets and developed a codebook (with example tweets) on the basis of these themes. The codebook is available in the Online Supplementary Materials.a Following the codebook, MEG and EBB independently, manually coded the contents of the tweets. Each content category was manually coded as a binary variable (0 = no, 1 = yes). Tweets were coded into the following sentiment categories: Provaccine sentiment, neutral sentiment, and antivaccine sentiment. Provaccine sentiment refers to tweets that explicitly communicated to readers that a vaccine is a safe and effective way of preventing diseases. Antivaccine sentiment refers to tweets that expressed skepticism or denial of vaccines as a safe and effective way of preventing diseases. Neutral sentiment refers to tweets with plain statements related to vaccine, such as its availability. Sentiment categories were merged into one categorical variable (1 = Neutral, 2 = Positive, 3 = Negative). Tweets that were deemed irrelevant or whose sentiment could not be determined (n = 81) were removed from further analysis. A total of 1344 tweets in English with categorized sentiments were analyzed (1326 were labeled as English in the Twitter metadata; 18 were labeled otherwise but were found to be in English through manual coding). Tweets that were identified as “antivaccine” (n = 325) were further manually coded into 2 themes that are not mutually exclusive (each being a binary variable): 1) perceived harmful risks, alleged side effects and/or deaths caused by vaccines (eg, autism, seizures, fatalities); and 2) distrust of government, pharmaceutical companies, scientists, and organizations that support vaccination efforts (eg, the Bill & Melinda Gates Foundation). Any antivaccine tweets that did not fall into either of the 2 themes were labeled as miscellaneous (tweets that are antivaccine but do not meet any of the content categories). Examples are given in the codebook in the Online Supplementary Materials.a

Statistical Analysis and Resolving URL

All statistical analyses in this experiment were performed in R Version 3.2.2 or 3.3.0 (R Foundation, Vienna, Austria). Negative binomial regression models were used because of overdispersion of the retweet frequency in this dataset. Because we postulated that the users’ characteristics could potentially be confounders to the statistical association between sentiment toward vaccine and retweet frequency, the users’ followers count, friends count, status count, and favorite count were included in our analysis. Given the highly skewed distributions of these variables, we converted these continuous variables into binary variables for better interpretation. The data were dichotomized as either below the geometric mean (labeled as 0) or not (labeled as 1). The cutoff value of a = 0.05 was chosen a priori for statistical significance. The short URLs of provaccine sentiment tweets and antivaccine sentiment tweets were resolved using R to their original URLs, and we extracted their domains. Descriptive statistics for URL domains that appeared 3 times or more are presented in the article.

Study B: #vaccineswork Twitter Dataset

Data

The data used for this study were purchased through GNIP Inc, which is a subsidiary of Twitter Inc in Boulder, CO. The dataset contained all tweets with the hashtag #vaccineswork from January 1, 2014, to April 30, 2015. The original dataset contained 194,259 tweets. Tweets therein with a threshold of greater than or equal to 100 retweets were grouped by subset from the original dataset for further analysis (N = 201). Retweet frequency and other metadata reported in this article were correct as of the date of data retrieval from GNIP Inc (early May 2015).

Manual Coding

Authors EBB and MEG developed a codebook by previewing the data for recurring themes. The codebook contained the following content categories: Mention of deaths and/or outbreaks of diseases that are vaccine-preventable; child vaccinations; mention of professional organizations, such as the Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO); mention of vaccine efficacy; mention of global vaccination importance; mention of people lacking access to vaccinations; tweets referring to World Immunization Awareness Week; mention of outbreaks of vaccine-preventable diseases; and provaccine statements directed at antivaccination sentiment. Tweets that did not meet any of these content categories were coded as miscellaneous. Content categories were not mutually exclusive (ie, the content of a tweet can be coded as “yes” in more than 1 category). Each content category was coded as a binary variable (0 = no, 1 = yes). Both EBB and MEG independently, manually coded all 201 tweets. Interrater reliability between the 2 coders was assessed by analyzing Cohen k for each content category. The k values for all content categories were > 0.8, implying a good interrater reliability.

The corresponding author (ICHF) further combined the content categories of “Mentions vaccines preventing deaths and/or outbreaks” and/or “Mentions efficacy of vaccines” into one category (Category 1), and those of “Mentions child vaccination” and/or “Mentions global vaccination improvement/efforts” into a single category (Category 2). Any tweet that was coded “yes” for Categories 1 and 2 was coded as Category 3, and any tweet that did not fall into Category 1 or 2 was coded as Category 0. A new categorical variable of content was thus created (see Online Supplementary Materialsa).

Statistical Analysis

All statistical analysis was performed using R version 3.2.2 or 3.3.0. Retweet frequency in this dataset of 201 manually coded tweets was overdispersed and truncated with a theoretical minimum value of 100. Therefore, a zero-truncated, negative binomial regression model was applied to new outcome variables17: Retweet truncated = Retweet frequency - 99. The regression model was applied after removing 4 apparent outliers from our dataset (bringing the total to 197 tweets). The cutoff value of a = 0.05 was chosen a priori for statistical significance.

RESULTS

Study A: #vaccine

Of the sample of 1344 #vaccine tweets that were coded with vaccine-related sentiments, provaccine tweets accounted for 32.4% (436/1344) of the sample, neutral tweets for 43.4% (583/1344), and antivaccine tweets for 24.2% (325/1344; Table 1). Regarding the proportion of tweets with URL links therein, there was no statistically significant difference (c2 = 4.4297, degrees of freedom = 2, p = 0.1092). In the antivaccine subcorpus of tweets (n = 325), 153 (47.1%) tweets mentioned only perceived risks and/or dangers of vaccines; 85 (26.2%) tweets mentioned only distrust of scientific entities such as the government, pharmaceutical companies, and scientists; 54 (16.6%) tweets mentioned both themes; and 33 (10.2%) tweets did not fit into either of the 2 themes (“miscellaneous”; Table 1). No significant differences in the proportion of tweets with URL links therein were observed among the 4 categories (c2 = 3.0012, degrees of freedom = 3, p = 0.3914).

In Table 2, we present the descriptive statistics of the retweet frequency, and the counts of users’ followers, friends, status updates, and favorites. These data were very skewed. For example, the median for retweet frequency for the sample and those for subsamples for positive, neutral, and negative sentiments were 0. For the users’ characteristics, the means were much larger than the medians. Therefore, for subsequent analysis, we dichotomized the users’ characteristics data as below the geometric mean or not, and thus converted the continuous variables into binary variables.

First, in the univariate analysis, both provaccine and antivaccine tweets had statistically significantly more retweets than neutral tweets; the users’ follower count, friend count, and status count were found to have statistically significant associations with retweet frequency (Table 3). In the multivariable regression analysis, provaccine tweets had 1.58 times as many retweets as neutral tweets (adjusted prevalence ratio = 1.5836, 95% confidence interval [CI] = 1.2130-2.0713, p < 0.001), and antivaccine tweets had 4.13 times as many retweets as neutral tweets (adjusted prevalence ratio = 4.1280, 95% CI = 3.1183-5.4901, p < 0.001) after controlling for users’ follower count, friend count, and status count (Table 3). Thus, antivaccine and provaccine #vaccine tweets differed in their retweet count, compared with tweets of neutral sentiment. Antivaccine tweets received more retweets than did provaccine tweets and neutral tweets. It is important to note that the retweet frequency of tweets posted by users with high follower count was 3.88 times (adjusted prevalence ratio = 3.8771; 95% CI = 2.9977-5.0295; p < 0.001) that of users with low follower count. To the contrary, users with high status count (ie, number of tweets ever tweeted) had 24% fewer retweets (prevalence ratio = 0.7597; 95% CI = 0.5856-0.9824; p = 0.033) than did users with low count of status updates.

Second, among the antivaccine subcorpus of tweets (n = 325), univariate negative binomial regression found that there were no significant differences between tweets that mentioned perceived risks and/or dangers of vaccines and those that did not (prevalence ratio = 0.74, 95% CI = 0.47-1.15, p = 0.20), and between tweets that mentioned distrust of government, pharmaceutical companies, scientists, and so on, and those that did not (prevalence ratio = 1.00, 95% CI = 0.65-1.56, p = 0.99). Thus, our hypothesis that different categories of contents among antivaccine #vaccine tweets differ in their retweet count was rejected.

Third, a total of 411 URL links were identified in 436 provaccine tweets: 36 tweets had 2 URLs, and 339 tweets had 1 URL. Among these links, Twitter (53; 12.9%), content curator Trap.it (14; 3.4%), and the CDC (8; 1.9%) were the top 3 domains. A total of 296 URL links were identified in 325 antivaccine tweets: 24 tweets had 2 URLs, and 248 had 1. Among these links, 26.7% of them were links to other tweets (44; 14.9%), YouTube videos (25; 8.4%), or Facebook (10; 3.4%). There were long tails with low frequency (1 or 2) for the URL domain frequency distributions among both provaccine and antivaccine tweets. Tables S1 and S2 in the Online Supplementary Materialsa detail the URL domains of URL links identified among provaccine and antivaccine #vaccine tweets.

Health Communication, Social Media, vaccines

Health Communication, Social Media, vaccines

Study B: #vaccineswork Twitter Dataset

Among our sample of 201 #vaccineswork tweets with 100 retweets or more, the most common theme observed was childhood vaccinations (40%; 81/201; Table 4). One in 5 tweets mentioned the global vaccination improvement/efforts (21%; 42/201). Nearly 3 in 10 tweets mentioned how vaccines can prevent outbreaks and deaths (29%; 58/201), 18% (37/201) mentioned a professional organization (eg, WHO or CDC), and 18% (36/201) discussed the efficacy of vaccines and vaccination of the population. Fifteen percent (31/201) mentioned a certain group of people (ie, a population, race/ethnicity, and/or country) and their lack of access to vaccines and routine vaccination; 12% (24/201) of tweets mentioned outbreaks and/or deaths that were caused by vaccine-preventable diseases; 10% (20/201) of tweets were focused on World Immunization Awareness Week; and 6% (13/201) of tweets were provaccination stances directed toward antivaccination sentiment (Table 4).

As previously described, some categories were dropped and others merged to create a categorical variable of 2 mutually exclusive categories and their combination for further regression analysis. After removing 4 outliers, the univariable zero-truncated negative binomial regression model was applied to the dataset (n = 197). No statistically significant association was observed between the categorical variable of combined categories and retweet frequency (Table S3 in Online Supplementary Materialsa).

Here, we described the 4 outliers that were most retweeted in our #vaccineswork dataset. The most retweeted tweet in the dataset was tweeted by American politician Hillary Clinton: “The science is clear: The earth is round, the sky is blue, and #vaccineswork. Let’s protect all our kids. #GrandmothersKnowBest.” The tweet was retweeted 33,164 times at the time when the dataset was purchased.

The second most retweeted tweet in this dataset was “*drops microphone* #antivax #vaccineswork #VaccinateYourKids http://t.co/1Nysbfkh7N” (retweet frequency = 5032). It was tweeted by @DocBastard, who described himself as a trauma surgeon in his user profile. This tweet ended with a link to an image of another physician’s social media post about how he handled parents who declined to have their children vaccinated on schedule.

The third most retweeted tweet was tweeted by the WHO (@WHO): “World Immunization Week starts today! Close the immunization gap, #VaccinesWork http://t.co/G3CjZKdhyv http://t.co/kZkiYPdEan” (retweet frequency = 1368). The first link in the tweet takes the user to a page on the WHO Web site about World Immunization Week. The second link takes the user to an infographic by the WHO that states, “Today 1 in 5 children worldwide is missing out on vital immunization.”

The fourth most retweeted tweet was tweeted by Sue Desmond-Hellmann, MD, MPH, the Chief Executive Officer of the Bill & Melinda Gates Foundation: “It’s impossible to argue with results like this. #vaccineswork http://t.co/yOeDVi2m0s” (User: @Sue Desmond-Hellmann; retweet frequency = 1182). The link therein takes the user to the tweet with an infographic that describes the decrease in percentage of annual morbidity of vaccine-preventable diseases in the US from the prevaccine era to the present.

Health Communication, Social Media, vaccines

Health Communication, Social Media, vaccines

Health Communication, Social Media, vaccines

Health Communication, Social Media, vaccines

Health Communication, Social Media, vaccines

DISCUSSION

In this study, we analyzed two datasets of vaccine-related tweets. We investigated the retweet frequency of a random sample of tweets within the #vaccine corpus, as well as the retweet frequency of a sample of highly retweeted tweets in the #vaccineswork corpus.

Among our random sample of #vaccine tweets, antivaccine tweets were retweeted more often, receiving 4.13 times as many retweets as neutral tweets, whereas provaccine tweets received 1.58 times as many retweets as neutral tweets. No differences in retweet frequency were observed for tweets carrying 2 content categories of antivaccine contents and those that did not.

Childhood vaccination appeared to be one of the most frequent topics in the #vaccineswork sample, with approximately 40% of the dataset mentioning childhood vaccination. This could be because of the increased interest in childhood vaccinations (eg, the number of vaccinations necessary, whether they are necessary at all, or their importance) in 2014 to 2015.18 Other top conversations in this corpus discussed the improvement in global vaccination and how vaccines can prevent outbreaks or deaths owing to vaccine-preventable diseases.

One of our key findings is that despite the provaccine health communication efforts made by public health agencies, as far as #vaccine tweets are concerned, on a tweet-by-tweet basis, antivaccine tweets may be receiving more attention (as reflected in the number of retweets) than provaccine tweets or neutral tweets. A potential explanation is that although the supporters of the antivaccine movements are a minority in the population, many of them are very committed to their cause and are active online.1 They retweeted tweets posted by like-minded individuals, forming an echo chamber.11 A study by Bahk et al12 found that antivaccine tweets persisted longer in a Twitter conversation about human papillomavirus than did the provaccine tweets. Our results added more evidence to the growing literature about the characteristics of antivaccine tweets.

The sources of information (URL domains) identified in the sample of #vaccine tweets can not only help public health professionals understand through which platforms people are gathering their information about vaccines but also can provide insight to what platforms or sites professionals should target when disseminating provaccine information. Given the use of Twitter across the opinion spectrum, it is not surprising that the top URL domain for both provaccine and antivaccine tweets was Twitter itself. In fact, it might reflect the growing trends that individuals rely on social media as their main source of news and information, compared with direct visits to Web sites of media or health organizations.19 Regarding URL domains in provaccine tweets in this corpus, many were major news sources (eg, The Washington Post), public health agencies (cdc.gov), and Web sites that communicate science and medicine; some were from social media such as Facebook and Instagram. To the contrary, URL domains in antivaccine tweets included sources from social media sites (eg, Facebook and YouTube) as well as Internet news sources and Web sites that are skeptical of vaccines and the medical establishment, and that advocate individuals’ right to decline vaccines for themselves and their children. Our results are congruent with the observed echo chamber effects on social media networks, in which people with similar ideas communicate with each other but not with people who disagree with them. As Del Vicario et al11 showed with Facebook data, users consuming scientific news and conspiracy theories are usually two distinct polarized communities that are homogeneous among themselves. Bessi and colleagues20 found that the debunking of conspiracy theories on Facebook were primarily read by users who frequently visited Facebook pages that shared scientific views and not by Facebook users who frequently consumed conspiracy theory Facebook posts; such observations cast doubt on the effectiveness of debunking conspiracy theories. A semantic network analysis of Internet articles shared by American Twitters users21 found that Internet contents of antivaccine sentiment put great emphasis on children and institutions, including the CDC, the pharmaceutical industry, the medical profession, the mainstream media, and the state. Distrust of the industry and government agencies that communicate provaccine scientific messages was found to be the key underlying theme of the antivaccine Internet articles. Our results added further evidence to the literature that people with antivaccine sentiment obtain and share information from alternative sources, probably because of their distrust of public health, medical, and pharmaceutical establishments. Therefore, simply releasing more scientific information online through Web sites and social media may not help.11

The outliers of the #vaccineswork dataset suggested that having key opinion leaders who are active on social media to communicate our scientific message that “vaccines work” is important, as it is through them that provaccine messages can reach users who normally would not follow social media accounts of health agencies.

This study has some limitations. First, our samples were small. Given the labor-intensive nature of manual coding, we could not manually code every tweet in our corpora. In Study A, we analyzed a 1% stratified random sample of #vaccine tweets that was representative of the corpus. In Study B, we analyzed a sample of #vaccineswork tweets that were retweeted 100 or more times. Our analysis was meaningful because we covered the most retweeted, and thus the most influential, tweets.

Second, our original coding scheme in Study B provided useful insights, but the nonmutually exclusive categories rendered regression analysis difficult to interpret. Further analysis after dropping outliers from the dataset, and after dropping some themes and merging the others, found no statistical association between retweet frequency and combined themes. This can be potentially explained as a result of the study design, because we decided to focus on the most retweeted tweets and therefore could not identify any differences in retweet frequency between the combined themes. Future research may investigate other factors that might have an influence on retweet frequency of highly retweeted tweets, such as the temporal trends associated with the topic at the time (ie, a topic that is getting increased media coverage), and the topic that led to spikes in social media traffic (as in a case study of spikes of Chinese social media posts about 42 notifiable infectious diseases22).

Third, our analysis of URL links in the #vaccine sample in Study A was limited to their domains. For URL links to social media platforms such as Twitter and Facebook, we did not analyze the users who posted the original social media posts to which the tweet was linked, or the contents of such posts (which was the focus of recent studies such as in Kang et al21). Fourth, retweet frequency is only one of several metrics used to measure engagement of social media users with the original posts. Some fake accounts or Internet “bots” could artificially boost the retweet frequency of some tweets. We did not have access to information that would allow us to distinguish retweets by “bots” from retweets by genuine users. Fifth, our analyses were confined to two corpora of tweets with hashtags #vaccine and #vaccineswork. Although this might limit the study’s generalizability to other tweets, our analyses were able to focus on tweets that laid emphasis on vaccine (through the use of hashtags). Future research on tweets with and without other hashtags may enlighten us on the generalizability of our findings. Sixth, we retrieved our tweets with two English-language hashtags and, therefore, retrieved tweets that were predominantly in English. Future research can extend to investigate how Twitter users in different linguocultural communities responded to provaccine and antivaccine messages on Twitter. A recent study found that Twitter users who used different languages reacted differently to an outbreak.23

CONCLUSION

Among #vaccine tweets, antivaccine tweets attracted more engagement than did provaccine tweets. Antivaccine tweets and provaccine tweets were 4.1 and 1.6 times as likely, respectively, to be retweeted as were vaccine-related tweets with neutral sentiments. Among #vaccineswork tweets, we did not find evidence of differences in retweet frequency between themes. Reaching out to key opinion leaders on Twitter to promote provaccine messages may help reach Twitter users who would be otherwise unreached by public health agencies.

a Online Supplementary Materials available at: www.thepermanentejournal.org/files/2018/17-138-Suppl.pdf

Disclosure Statement

Dr Fung received salary support from the Centers for Disease Control and Prevention (16IPA1609578). The data used in Study B were purchased using the start-up funds that Dr Fung received at the Jiann-Ping Hsu College of Public Health, Georgia Southern University, in Statesboro, GA. This article is not related to the Centers for Disease Control and Prevention-funded project of Dr Fung. The opinions expressed in this article do not represent the official positions of the Centers for Disease Control and Prevention or the US Government.

The author(s) have no conflicts of interest to disclose.

Acknowledgments

Kathleen Louden, ELS, of Louden Health Communications provided editorial assistance.

How to Cite this Article

Blankenship EB, Goff ME, Yin J, et al. Sentiment, contents, and retweets: A study of two vaccine-related twitter datasets. Perm J 2018;22:17-138. DOI: https://doi.org/10.7812/TPP/17-138

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