Our data collection approach yielded 1073 questions and 7479 answers from Quora. Based on all collected data, both the oldest question and the oldest answer were posted on May 10, 2019 (before the pandemic and which was excluded from analysis), and the most recent question and answer were published on October 7, 2021, and October 20, 2021 (near the date of data collection commencement). After applying our binary coding approach, we identified 508 (47.34%) questions related to COVID-19 vaccine clinical trials. In addition, based on our manual annotation and content coding, we identified 3105 answers from selected relevant questions, of which 2542 (33.99%) answers were identified as related to COVID-19 vaccine clinical trial-related topics, which comprised responses from a total of 1154 unique Quora user accounts. From these relevant posts, the timeline of the Quora questions and answers that included readable timestamps had the earliest question dated May 1, 2020, and the latest question dated October 7, 2021. Corresponding to these questions, the oldest answer was posted on January 10, 2020, and the most recent response was posted on October 17, 2021.

According to our qualitative analysis and inductive coding approach, 28 topics were derived under two major parent domains and seven subcodes (refer to Table 2 for a complete breakdown of the stratification of these codes and anonymized and paraphrased examples from Quora). According to our inductive coding, all detected topics could be classified into two major domains: COVID-19 vaccine clinical trial participation (491/2542, 19.32%); and COVID-19 vaccine clinical trial design, process, and results (2051/2542, 80.68%).

According to the answers identified from the trial participation parent topic (parent code A), which focused on discussions related to participation in COVID-19 vaccine clinical trials, we were able to identify user conversations focusing on sharing specific concerns about trials (A-1-a, A-1-b), trial experiences (A-1-d), trial knowledge (A-1-e, A-1-f), and the reasons (A-1-c) for participating in a COVID-19 vaccine clinical trial as discussed by actual trial participants (n = 238) (see Fig. 1 for content classification breakdown). Among these topics, sharing the experience of participating, including topics related to side effects (A-1-d, n = 61) and sharing trial knowledge topics (A-1-3, n = 61), had the highest volume of posts, followed by the topic concerning safety of COVID-19 vaccine clinical trials (A-1-a, n = 44). We also observed specific concerns from trial participants about trial participation and subsequent vaccine access eligibility. Specifically, users questioned whether if other vaccines were approved during their trial participation, they would be able to get vaccinated with a subsequently approved vaccine or whether they would need to withdraw from trial participation (A-1-b, n = 9; A-1-f, n = 36). There were also 27 posts that shared the specific reason why a user participated in a clinical trial (A-1-c) including: having watched a family member die from COVID-19 and wanting to prevent the same from happening to others, feeling proud of trial participation based on the belief that they were helping others, and wanting to get a quick and free vaccination. Among this trial participation parent topic, we were also able to detect discussion focusing on sharing trial recruitment information (A-2-a, n = 27) and discussion related to willingness and unwillingness to participate in a COVID-19 vaccine clinical trial from those who did not actually participate (A-2-b, n = 226). For example, a group of people reported they would rather be infected with COVID-19 virus than get a vaccine, so they would not participate in a clinical trial.

Content Breakdown into Sub-topics

In the clinical trial design, process, and results domain (parent code B), which focused on online user discussions related to public opinion about COVID-19 vaccine clinical trials, we were able to identify topics about the length (B-1-a, B-1-b), eligibility (B-2-[a-d]), the mechanism (B-3-[a-d]), stages (B-4-a), and the results (B-5-[a-h]) of existing COVID-19 vaccine clinical trials. Among all of these six sub-topics, the most dominant topic were discussions related to trial results (B-5[a-f], n = 798), including questions and answers of whether the results of specific COVID-19 vaccine clinical trials could be trusted and whether a vaccine approved based on those trial results could be considered safe (B-5-a, n = 247; B-5-d, n = 160); discussion about the results of trials taking place outside of the United States (B-5-b, n = 189); discussion about vaccine efficacy in different trials and efficacy for COVID-19 variants (B-5-c, n = 97; B-5-g, n = 55); discussion about purported safety events and long-term health effects (B-5-e, n = 39); and general public distrust of the results of trials based on claims about the vaccine manufacturer (B-5-h, n = 5). The second-largest sub-topic in this domain was related to mechanisms of current COVID-19 vaccine clinical trials (B-3-[a-d], n = 572). These conversations included discussions about: how efficacy of the vaccine is proven, are the participants being exposed to the COVID-19 virus during the trial (B-3-a, n = 163), what is the mRNA vaccine, and why is there a need for a placebo in a clinical trial (B-3-b, n = 151), how does the emergency use authorization impact the approval of a COVID-19 vaccine (B-3-c, n = 83), and what are the common processes and regulations of a clinical trial (B-3-d, n = 175). In this domain, we also observed topics that were related to the progress of different trials (B-4-a, n = 537); different opinions on the length of COVID-19 vaccine clinical trials (B-1-a, n = 12; B-1-b, a = 6); and conversations related to the eligibility to enroll in a trial (B-2-[a-d]), including whether there was sufficient participant representation (B-2-a, n = 59), health condition representation (B-2-b, n = 14), age representation (B-2-c, n = 42), and racial representation (B-2-d, n = 11).

From a timeline perspective, the volume of the answers associated with COVID-19 vaccine clinical trials started increasing from the beginning of the data collection period until September 2020, representing the peak point of answers posted, and beginning in October 2020, the volume of answers started decreasing until the end of our data collection period. The most predominant topic detected earlier in the COVID-19 pandemic included discussion of participation in the COVID-19 vaccine clinical trial and a user debate regarding other countries’ vaccine development progress (A-2-a, B-5-b). Topics that emerged the latest in this study were associated with the eligibility of participating in trials, specifically, the discussion about different age representation in COVID-19 vaccine clinical trials (B-2-c) (see Fig. 2 for timeline associated with topics reviewed).

Timeline associated with topics

Among all identified 508 Quora questions that were related to COVID-19 vaccine clinical trial topics, the number of answers for each question varied from a minimum of 1 answer to a max of 112 answers, averaging a 5.58 answer rate. The number of relevant answers for each question varied from a minimum of 1 answer to a maximum of 107 answers, averaging a 5.12 relevant answer rate. When analyzing the top 10 relevant answered questions (see Table 3), 3 of the questions (Question numbers 2,5,10) were related to clinical trial participation. These answered questions included users discussing their willingness to enroll their children or themselves into a COVID-19 vaccine clinical trial and the specific experiences of trial participation. The other 7 remaining questions were related to public opinion about COVID-19 vaccine clinical trials’ design/ process/ results (Question numbers 1,3,4,6,7,8,9), including asking how people think about other countries’ vaccine development progress, the safety of the approved vaccines, and if applicable regulations had been followed at trial completion.

According to all 2542 signal answers, we were able to find a total of 34,835 upvote interactions from 1400 relevant answers. The most accepted answer had 24,000 upvotes, though 142 answers did not have any upvoting. Based on the upvote number for the answers in each sub-topic, we observed discussions about the sub-topic related to results of COVID-19 clinical trials (B-5-[a-h]) had the most answers (n = 798) and upvoting interactions (n = 29,256, 83.98%) (See Fig. 3).

Relevant Answer and Upvote Number Breakdown into Sub-topics

We also identified 4 questions and 12 answers with a total of 283 upvotes directly related to health equity topics, including questions discussing: (a) whether race is a social construct, and why is it important that COVID-19 vaccine trials involve a minimum number of racial or ethnic minority participants; (b) asking how many Blacks or African Americans have participated in COVID-19 vaccine trials; (c) discussion of why recruitment was difficult for certain racial or ethnic minority populations for COVID-19 vaccine trials; and (d) questions of why some COVID-19 vaccine trials had a lag time when enrolling racial and ethnic minority participants. The most upvoted answer (n = 140) explains why it is essential for a clinical trial to include participants from each racial or ethnic minority group.

From 2542 relevant answers confirmed as related to COVID-19 vaccine clinical trial topics, 2033 (79.98%) answers had sufficient metadata in publicly available user profiles to identify the user’s reported country of residence, and 298 (11.72%) answer posts had self-identified racial or ethnic minority information. Among all 2033 answers with geographic location data, we observed that users reported they resided in 57 countries, and based on the distribution of these answers, the top five countries were the United States (1056/2033, 51.94%), England (282/2033, 13.87%), India (233/2033, 11.45%), Canada (113/2033, 6.54%), and Australia (89/2033, 4.38%). According to users’ racial and ethnic user profile information, we identified five answers posted from Black or African American users, 292 answers from Asian users, and one from a Hispanic or Latino user. Among all of the 298 answers from self-identified racial or ethnic minority group users, 30 of them (Black or African American = 5, Asian = 24, and Hispanic or Latino = 1) identified as current U.S. residents, with nine answers related to trial participation, including explaining to other users why they believed a trial was safe, discussing why as a Black or African American the user did not want to participate in any COVID-19 vaccine clinical trial, and sharing resources and knowledge about COVID-19 vaccine trials (A-1-[a,d,f],A-2-[a,d]). An additional 21 answers from racial and ethnic minority users were related to trial design/process and results, including expressing their trust of the COVID-19 vaccine, explaining to others their knowledge of the mRNA vaccine and the mechanism of the trial design, discussing why teenagers are not included in certain phases of a trial, as well as the discussion about the efficacy of certain vaccine trials. (B-2-b, B-3-[a-d], B-4-a, B-5-[a,c,e,g]).