Confidence and Receptivity for COVID-19 Vaccines: A Rapid Systematic Review

While COVID-19 continues raging worldwide, effective vaccines are highly anticipated. However, vaccine hesitancy is widespread. Survey results on uptake intentions vary and continue to change. This review compared trends and synthesized findings in vaccination receptivity over time across US and international polls, assessing survey design influences and evaluating context to inform policies and practices. Data sources included academic literature (PubMed, Embase, and PsycINFO following PRISMA guidelines), news and official reports published by 20 October 2020. Two researchers independently screened potential peer-reviewed articles and syndicated polls for eligibility; 126 studies and surveys were selected. Declining vaccine acceptance (from >70% in March to <50% in October) with demographic, socioeconomic, and partisan divides was observed. Perceived risk, concerns over vaccine safety and effectiveness, doctors’ recommendations, and inoculation history were common factors. Impacts of regional infection rates, gender, and personal COVID-19 experience were inconclusive. Unique COVID-19 factors included political party orientation, doubts toward expedited development/approval process, and perceived political interference. Many receptive participants preferred to wait until others have taken the vaccine; mandates could increase resistance. Survey wording and answer options showed influence on responses. To achieve herd immunity, communication campaigns are immediately needed, focusing on transparency and restoring trust in health authorities.


Introduction
The COVID-19 pandemic persists with resurgent waves while debates intensify about reinstituting lockdowns, civil liberties, and societal livelihood. Vaccines have become the hopeful savior to end the worst global health and economic crisis of living memory. Beyond the complex logistics of developing and testing, mass manufacturing, and distribution, the public's confidence and acceptance for the vaccines are unclear and changing [1,2], rendering achieving herd immunity challenging.
Vaccine hesitancy can be dated back to the 1800s [3]. Well before the pandemic, the World Health Organization in 2019 identified it as a top global health threat [4]. Studies regarding intention to get vaccinated against COVID-19 have been published since early 2020 with great variations in question formats and results [5][6][7][8][9][10]. Many reported a pattern of increasing doubts about vaccine safety and declining receptivity [11][12][13]. However, differences in their findings and factors associated with vaccine hesitancy unique to COVID- 19 have not been systematically examined.
A comprehensive understanding of the current vaccine sentiment and potential determinants of people's behavior is critical for planning effective health communications to encourage uptake and successfully implementing population immunization. The objectives Overall, the research design and data collection procedures of the included studies were deemed appropriate, conducted mostly by reputable pollsters (e.g., Ipsos, Pew Research, USA Today). Common quality issues included unreported non-response rates and not explicitly describing whether the percentage tabulations included missing data. A large majority of the surveys polled 1000-3000 participants and five polled over 10,000. All except seven had national/state representative samples through random selection from the targeted population (e.g., via voter registration or phone numbers) or large national/international opt-in panels, many stratified by demographics. The other seven were convenience samples utilizing social media [2,7,[16][17][18] or recruiting posters [19,20].
The majority of the surveys were US-based; 16 (12.7%) international surveys covered a total of 31 countries, predominately conducted in the earlier study period. Eighty-seven of the surveys were among 15 series of recurring polls. Two major longitudinal surveys were conducted by Morning Consult with 33 surveys starting late February and YouGov (partnering with The Economist and Yahoo News) with 17 surveys since May. The summary table in Appendix A Table A4 described each survey's dates, country (if non-US), sample size, question wording, answer options, responses, key findings, and relevant factors.
Less frequently discussed were cost [47], willingness to pay [2,34,56], and country of vaccine origin. Cost ranked low as a concern for Americans [5]. One survey reported that 17.1% would get the vaccine only if covered by insurance [54] and another found 49% expected it to be free (paid by insurance or government) [56]. In America, US-made vaccines were more trusted than China-made [53,57] or foreign-developed [5,53]. Most Chinese (64%) expressed no preference for domestic or foreign-made [34]. National (but not necessarily state) coronavirus infection and mortality rates [9,21,23,58], perceived risk of infection [2,7,42] and disease severity [2,53] were predictors of vaccination intentions. The impacts of having been infected oneself or knowing a friend/family who had and the desire to protect oneself or others were also cited but less conclusive. Some studies indicated positive association [19,53], while others found no correlation [21]. One study reported only 55% of those worrying about themselves or family members getting infected would get vaccinated [49].
Three international studies investigated healthcare professionals' attitudes and found similar concerns about vaccine safety and effectiveness and receptivity predictors including previous vaccination history, perceived risk or exposure, and being older, male, or a doctor [7,55,62]. Healthcare workers in Indonesia had greater acceptance than the public (OR: 1.57, 95% CI: 1.12-2.20) [63] while nurses in Hong Kong indicated low intention (40%) [7]. Israeli doctors reported slightly higher self-acceptance (78% vs. 75%), but were less likely to vaccinate their children than the public (60% vs. 70%) [62].

Assessing the Impact of Survey Design
To examine the influence of question framing, Figure 2 plotted the rates of affirmative responses to COVID-19 vaccine intention questions across the past eight months, differentiated US-based and international surveys for comparison. Data from Morning Consult and YouGov series provided strong evidence of the declining receptivity based on consistent questioning. Other surveys, though using varied question wording, showed a similar pattern with few but some exceptions.
Declines in the two longitudinal surveys were almost parallel over the study period, with YouGov's findings consistently 9-18% lower than Morning Consult's. YouGov posed the question neutrally as "if and when a coronavirus vaccine becomes available, will you get vaccinated?" Morning Consult worded it slightly differently, "if a vaccine that protects from the coronavirus became available, would you get vaccinated or not?" Similarly, other surveys that reported higher receptivity often framed the question in a more positive way or provided some assurance: e.g., "FDA approved" [40,64], "prevent" [6,65] or "against coronavirus" [18,34,49], "safe and effective" [16,66], "successfully developed" [29], and "recommended for me" [9]. Some surveys tagged additional conditions that triggered higher interest, such as "free" or "at no cost" [6,40,67] and "US-developed" [57]; other conditions heightened hesitancy, including "first generation of vaccine" [45], "as soon as possible" [68,69], and "approved or released before the US election" [70][71][72]. Examples of such effects and outliers were illustrated with annotated speech bubbles in the following graphs.
Assessing answer choice influence, we separated surveys into Group A with two or three answer options (yes/no/not sure or don't know) and Group B with four or five options (e.g., very likely/somewhat likely/neutral/somewhat unlikely/very unlikely, definitely/probably/probably not/definitely not). Figure 3 plotted the percentages of participants who picked the first answer in each of the two groups and demonstrated the differences between the two survey designs. Responses were more spread out when there were more options (as in Group B) and thus produced seemingly lower percentages of affirmative answers. Pollsters often combine the results of the first or last two answer categories in writing news articles for more eye-catching headlines, such as "Two in three Americans likely to get coronavirus vaccine [73]." In such case, attention is needed to distinguish and accurately interpret the results.  Further, simply looking at the ratio of people answering yes or likely does not tell the whole story. When answer options included different timings for vaccination, more people chose to wait than get it as soon as possible [54] (e.g., 45% vs. 28% [74]). One survey asked "How likely are you to get a COVID-19 vaccine as soon as it becomes available?" with only two answer choices-likely or unlikely, which by comparison received relatively high (67%) affirmatives [75].
It is equally important to assess trends of vaccine hesitancy and refusal. Figure 4 illustrated the increasing ratio of respondents indicating low or no intention to vaccinate and the summary table (Appendix A Table A4) documented each answer choice frequency.

Contextual and COVID-19 Factors
Several factors are unique to this pandemic due to the novelties and magnitude of COVID-19 and current highly polarized partisan environment [13,19,[76][77][78]. The expedited vaccine development has caused apprehension and distrust [5,10,30,60,79], particularly the Emergency Use Authorization process [53]. While 33% were confident that the FDA will only approve the vaccine if it is safe [51], 41% believed the vaccine will be made available before proven safe and effective [26]. Seventy-five percent worried about the safety of fast-tracking [28]; 11% would be more likely to take a vaccine if Operation Warp Speed suggested it [80].
Hesitancy was manifested in the preference to wait [54]: 60% were unlikely to get the first generation of vaccine [56]; 64% endorsed prioritizing full testing even if delaying availability [57]. Among individual states, 41.6-51% would wait until others have taken it [23,25,58,74,[81][82][83]. In China, while 91.3% showed intention to accept, 47.8% would delay until confirmed safe [29]. On the other hand, one international survey found 43% willing to accept less stringent standards [20]; an American survey reported that 59% agreed that providing more people access outweighs the risks of an accelerated process [30].
Three studies analyzed the prevalence and impact of conspiracy theories [84][85][86]; 33% of respondents in the US and 50% in England showed some conspiracy thinking [84,85]. Respondents with higher skepticism had lower perceived risk and trust in government or professionals, and thus higher doubts and objections to vaccination [85,86]. Mainstream news could counter misinformation and utilizing politically conservative outlets and doctor's communications were suggested for accurate messaging [84,86].
Coinciding with the timing of the US presidential election, many polls included politically oriented questions. Partisan influences were evident, with persistent vaccine attitude gaps between Democrats and Republicans [27,50,76] (80% vs. 48% acceptance [40]; 74% vs. 54% belief in clinical trial importance [42]). The chasm extended to risk perceptions; 42% vs. 19% believed coronavirus is a severe health threat [76]. Conversely, in France, the Far Right parties had higher willingness to vaccinate [10]. Declining trust of information sources and authorities was also observed [24,56,60,87,88]: 50% thought President Trump had influence over FDA decisions [89]; 82% of Democrats and 72% of Republicans worried vaccine approval was driven more by politics than science [75].
In a large multi-national survey, 71.5% would likely get vaccinated and 61.4% would comply if employers suggested doing so [21]. In the US, 65% believed parents should be required to vaccinate [90]; but the rate of refusal grew from 24% to 42 [54,91]. Parents may have different considerations for vaccinating their children than themselves. One survey reported 76.02% vs. 74.38% receptivity and another 45% vs. 36.2% [5,54]; 58% would do so as soon as possible [51], though having chronic illness was a deterrence [19]. Those who indicated refusal for themselves also would not vaccinate their children [48].

Discussion
This review is the first examining trends of over 100 surveys capturing COVID-19 vaccine receptivity. Although there appear to be consistent declining trends, there have been differences in survey presentations and findings. The deep fissures in American society by income, race, and political affiliation revealed by the pandemic are reflected in vaccine attitudes. Our results showed that vaccine hesitancy is universal across countries, states, and subgroups (including healthcare providers and parents), so are its determinants-perceived disease or outbreak severity, infection risk, and vaccine safety, effectiveness, and necessity. Influenza vaccination history, trust in government, and doctor's recommendations are important facilitators for vaccine confidence and acceptance. These findings align with previous research on other vaccines [92][93][94][95]. Nonetheless, increasing daily cases and deaths did not prevent double-digit declines in vaccination intention since its highest point in early April [27].
Socioeconomic and racial issues pertaining to health disparity during regular times and other epidemics persist here [96,97]. Minorities, lower income, and less educated individuals are disproportionally more susceptible to COVID-19 [98,99]. Their considerably lower vaccine acceptance requires special attention, including acknowledging the source and addressing the effect of their chronic distrust of health authorities in order to confront the vicious cycle of skepticism and inferior health outcomes. Much of minorities' reservation or resistance toward medical research and the healthcare system originated from historical events (e.g., unethical experimentation among Blacks in the Tuskegee syphilis study) as well as ongoing perceived bias in clinical interactions and treatments [97,100,101]. Vaccine distribution prioritization should consider these disadvantaged groups as part of the high-risk population, considering their work or underlying health conditions, to improve equity [102].
Men in general are more receptive of COVID-19 vaccines and, as evident in the literature, more inclined to adopt pharmaceutical interventions [103], including vaccination [104][105][106]. Women are more likely to worry about catching coronavirus, concerned about side effects [107], and take protective measures (e.g., masking, handwashing, and social distancing) [108,109]. Such prevention-orientation variance, not limited to gender difference, calls for tailored communications and appeals. Future research could explore whether people perceive higher risk in taking a new vaccine than getting infected with a novel disease.
Often dominating the vaccine discussion in this pandemic are unique expedited development, perceived political interference, and ubiquitous misinformation that have dampened confidence in the rigor of the approval process and the use of the vaccine itself. Trust in authorities has fallen, greater in federal than state or local governments (53% in mid-March to 34% in October) [72]. Major news media believed President Trump's repeated pre-election promises of a vaccine "within weeks" or by November often "fueled fears" and "heightened concerns" of a rushed process [110,111]. Our polarized electorate mirrors that of the population with large differences across groups. The devastating economic consequences of the pandemic and the heated US presidential election filled with clashing rhetoric have further divided the society along the party line, partitioning people's opinions in the reality of COVID-19 and the life-saving measure against it. Moreover, the proliferation of conspiracy theories surrounding coronavirus and the vaccines, combined with existing anti-vaccine movement adds another uncertain dimension to vaccine decisions [86,112,113]. Detected misinformation or the spread of "fake news" must be quickly denounced and sources isolated.
Emphasizing transparency and adherence to scientific standards throughout the vaccine development, approval, and distribution processes could restore confidence. In early September, the pharmaceutical industry's joint pledge to file for emergency authorization only when they have evidence proving the safety and effectiveness in clinical trials [114] boosted pharma's reputation to 49% positive view in a national poll [115], compared to 32% pre-COVID-19 [116]. The FDA advisory committee's public meetings with independent experts also provided some reassurance [110]. Second to doctors, Centers for Disease Control and Prevention (CDC) and national public health officials remain the most trusted sources for accurate information (71% and 69%, respectively, though decreased since mid-March) [72]; these figures are significant influencers of people's health behavior and should be the main communicators in vaccine campaigns to encourage acceptance [117].
The impact of framing and wording choices demonstrated in the comparative analyses offers lessons to guide the urgent development of a critically needed national vaccine campaign and improve future study design supporting continued vaccine hesitancy surveillance [118,119]. For example, posing a question such as, "Would you be willing to get the vaccine to protect yourself and your family?" casts a more positive mindset than asking "how risky do you think it would be to get vaccinated?" Yet, the latter could be turned into an educational opportunity to correct misconception. Though a vaccine could not be distributed without FDA approval, from the surveys many people do not seem to equate a vaccine becoming available to having been approved with proper safety protocols in place. Delineations on such issues could debunk confusion and doubts.
Subgroups with different characteristics and opinions require customized messages, presentations, and channels [120]. It is essential to ensure that intention translates into actual uptake [121]. Furthermore, hesitancy when compared to avoidance or refusal, is a dynamic state that opens the door for persuasion [22,118]. Campaigns targeting those who responded "likely," "probably," or "not sure" regarding vaccine intention would be more fruitful than trying to convert those who stated "no" or "definitely not." People need to believe that a behavior is beneficial, even vital, in order to adopt it [122]. Messages should focus on the safety and efficacy of vaccines as well as clarify the value and necessity of immunization in people's belief system (e.g., stressing that many vaccines have helped eradiate or control deadly diseases that we are no longer aware of or concerned about because vaccines worked).
Learning from the delayed and conflicting communications about mask wearing and the protest against it, messages tailored to individuals' disposition (e.g., protecting self or others and family, freedom of choice vs. civic responsibility) would be more effective. Though not explicitly covered in the surveys reviewed, the intricate balance between preserving individual rights and securing population health has generated dis-cords throughout the pandemic, from mask requirement, lockdowns or curfews, to mass vaccination. Several studies underscored the likely resistance mandates may elicit, even among originally receptive groups [23,25,81,83]. Framing vaccination as a smart, purposeful personal decision, emphasizing individual's autonomy could yield greater results. In addition to traditional media and official websites for disseminating current and accurate information, since social media is a popular source of news as well as misinformation for many [123,124], it should be a key channel in messaging and combating anti-vaccine or conspiracy theories.
Communication strategies could utilize positive cues to action, including encouragement from loved ones and trusted figures such as physicians and religious leaders, sharing personal stories, and peer pressure [125]. Studies also have shown social expectation and portraying anticipated regret from inaction to be potential motivators for vaccination [104,126]. Furthermore, accompanying the rollouts of vaccines with short supply and complex delivery requirements (e.g., low-temperature storage and double dosage), campaign objectives should instill confidence not just in the safety of the medical intervention but also in the manufacturing, transportation, access, and equitable distribution to alleviate concerns or distrust.
This review is subject to limitations. Studies retrieved from the scholarly databases may not provide the most up-to-date public opinions due to the review and publication processes. Though Google search is less customary for systematic reviews, research guides suggested it as a gray literature source and suitable in locating surveys for this review [127][128][129]. The inclusion of studies was not exhaustive (with mostly US-based surveys), but covered a large number of major polls and important factors for a comprehensive picture of the trends. Future research would benefit from qualitative inquiries to allow for elaborations on non-pre-defined factors. Longitudinal studies could re-poll the same participants to detect triggers for attitude changes.
Caution should be taken in interpreting and using the results since intention or survey responses may not directly predict future behavior [130]. Moreover, opinions may change, especially amid the raging pandemic. Continued vaccine receptivity tracking could reveal whether the reported clinical trials incidents or outcomes and subsequent introductions of vaccines or new treatments would further change people's minds about getting vaccinated.

Conclusions
Vaccine hesitancy is an imminent threat in the battle against COVID-19 because achieving herd immunity depends on the efficacy of the vaccine itself and the population's willingness to accept it. This review offered a sweeping examination of the evolving vaccine attitudes since the early stage of the pandemic to inform policy makers and public health professionals in campaign planning and communications. Consistent with the literature, demographic and socioeconomic divides in receptivity are present in these surveys and the partisan nature of some indicators is unprecedented. Multiple factors, including perceived disease risk and vaccine safety concern as well as question presentation, could influence responses and ultimately actions. The power of words and framing illustrated in this review helps shed light on strategic communication for motivating positive, collective pandemic response.
On-going campaign content adjustments and monitoring responses should not be overlooked. Once vaccination starts, the likely decrease in new COVID-19 cases needs to be accurately highlighted as the outcome of vaccine uptake rather than being interpreted as lessened risk, something that could reduce the perceived need for vaccination.

Acknowledgments:
The authors would like to thank Brooke Bier for her assistance in collecting and compiling data.

Conflicts of Interest:
The authors declare no conflict of interest.  Asked if vaccine should be required, free, development accelerated skipping clinical trials, benefits outweigh risks. 74% likely to get if passes trials; 30% "be in a rush" to get FDA-approved vaccine. 66% believe vaccine more effective than social distancing to control spread      Tufts Univ Research Group on Equity in Health, Wealth and Civic Engagement [33] 1267 If a vaccine were available today, would you be willing to get it?

Appendix A. Literature Search Strategy
(not exact wording) Yes/don't know/no 57% 24% 18% Examined hesitation in equity context. More likely: Whites, Hispanics, Democrats, more formal edu, higher income. Further widened "the gap in health outcomes"    . 76% concern about side effects-major reason; 77% thought likely it will be approved before fully known safe and effective; 78% concern moving too fast vs. 20% too slow.     Democratic 15% more likely to get the vaccine. 10/7-10/10 (2 of 2) STAT/The Harris Poll [147] 2050 How likely are you to get a COVID-19 vaccine as soon as it becomes available?
Likely/unlikely 58% 48% Declined from 69% in August. 59% Whites and 43% Blacks. 40% more likely to get vaccine once Trump tested positive for COVID, 41% said their opinions had not changed