key: cord-0774332-f6orwwi9 authors: Nikolovski, J.; Koldijk, M.; Weverling, G. J.; Spertus, J.; Turakhia, M.; Saxon, L.; Gibson, C. M.; Whang, J.; Sarich, T.; Zambon, R.; Ezeanochie, N.; Turgiss, J.; Jones, R.; Stoddard, J.; Burton, P.; Navar, A. M. title: Factors indicating intention to vaccinate with a COVID-19 vaccine among older U.S. Adults date: 2021-01-11 journal: nan DOI: 10.1101/2021.01.10.20248831 sha: 94267284493c47d17ef38f4536981e5f969f2608 doc_id: 774332 cord_uid: f6orwwi9 BACKGROUND The success of vaccination efforts to curb the COVID-19 pandemic will require broad public uptake of immunization and highlights the importance of understanding factors associated with willingness to receive a vaccine. METHODS Adults enrolled in the Heartline clinical study were invited to complete a COVID-19 vaccine assessment through the Heartline mobile application between November 6-20, 2020. Factors associated with willingness to receive a COVID-19 vaccine were evaluated using an ordered logistic regression as well as a Random Forest classification algorithm. RESULTS Among 9,106 study participants, 81.3% (n=7402) responded and had available demographic data. The majority (91.3%) reported a willingness to be vaccinated. Factors most strongly associated with vaccine willingness were beliefs about the safety and efficacy of COVID-19 vaccines and vaccines in general. Women and Black or African American respondents reported lower willingness to vaccinate. Among those less willing to get vaccinated, 66.2% said that they would talk with their health provider before making a decision. During the study, positive results from the first COVID-19 vaccine outcome study were released; vaccine willingness increased after this report. CONCLUSIONS Even among older adults at high-risk for COVID-19 complications who are participating in a longitudinal clinical study, 1 in 11 reported lack of willingness to receive COVID-19 vaccine in November 2020. Variability in vaccine willingness by gender, race, education, and income suggests the potential for uneven vaccine uptake. Education by health providers directed toward assuaging concerns about vaccine safety and efficacy can help improve vaccine acceptance among those less willing. With the recent FDA Emergency Use Authorization (EUA) for two COVID-19 vaccines, significant attention is now being placed on whether sufficient numbers of the public will be willing to be immunized to control the pandemic and how to ensure the public is adequately informed about the vaccine. 1, 2, 3 Surveys in the United States showed an initial decline in reported willingness to receive a COVID-19 vaccine, 4,5,6,7 though more recent data appear more promising. 5, 8 Individual perceptions about vaccines and about COVID-19 can strongly influence the decision to vaccinate against COVID-19, and are likely more associated with vaccine behaviors than demographics alone. 9,10,11 Understanding these potentially modifiable factors are important to develop public health strategies to overcome vaccine hesitancy, especially among older and higher risk populations. 12 Smartphone-based research can facilitate rapid data collection for timely research questions. To accelerate public health's understanding of current perspectives on vaccinations, we surveyed subjects already participating in a smartphone-based clinical trial, the Heartline TM Study, a virtual clinical study that is enrolling U.S. adults age 65 years and older. These participants are at high risk of COVID-19 related morbidity and mortality due to their age, and thus have a large potential benefit from immunization. In order to understand factors associated with and indicative of willingness to vaccinate in this higher risk population, we deployed a vaccine survey to all participants through the Heartline TM platform in November, 2020. All rights reserved. No reuse allowed without permission. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted January 11, 2021. ; https://doi.org/10.1101/2021.01.10.20248831 doi: medRxiv preprint On February 25, 2020, enrollment began into The Heartline TM Study (clinicaltrials.gov, NCT04276441 and https://heartline.com/), a large heart health clinical study in the United States. Eligibility requirements include age 65 and older, possessing an iPhone 6s or later, current Original Medicare beneficiary, U.S. resident, and English-speaking (see clinicaltrials.gov, NCT04276441 for complete inclusion and exclusion criteria). The Heartline TM Study is investigating if wearable and custom-built mobile app technologies can enable earlier detection of atrial fibrillation (AF), reduce the incidence of clinical events, and improve adherence with oral anticoagulants in those with AF. The study is completely virtual, without the need for study site visits, and is conducted on the Heartline TM app. The study platform is designed to introduce novel surveys as needed throughout the study. The study protocol was approved by an IRB and all participants provide informed consent to analyze de-identified data, including surveys delivered through the Heartline TM app. Willingness to vaccinate against COVID-19 was assessed through an optional survey through the Heartline TM app between November 6 and 20, 2020. The assessment was framed by the World Health Organization recommended Capability, Opportunity, Motivation and Behavior model (COM-B) model for addressing vaccine hesitancy and acceptance. 13 The assessment included questions regarding beliefs about vaccines in general, beliefs about COVID-19 and the COVID-19 vaccine, and opinions on vaccine dosing and potential side effects (see Supplement S1 for the complete assessment). The assessment was offered to all study participants. Demographic data were collected at the time of study enrollment, which included race and gender by self-report. The primary outcome of the study was self-reported willingness to receive a COVID-19 vaccine. This was captured on a four-point scale (very willing, somewhat willing, not very willing, not at all willing). To evaluate factors associated with vaccine willingness, we applied two different analytic approaches. First, determinants of willingness to be vaccinated were evaluated using an ordered univariate logistic regression model with the 4 levels of willingness to be vaccinated as the outcome while adjusting for race (Asian, Black or African American, White and other) and gender. Next, to identify a set of determinants to separate those who are willing to vaccinate from those who are not, recursive feature elimination in combination with a Random Forest classification algorithm 15 was performed. In this analysis, willingness to vaccinate was classified into two categories: willing to vaccinate (combining very willing with somewhat willing) and not willing to vaccinate (combining not at all willing with not very willing). The algorithm was trained using a dataset that was randomly split by stratum (either not willing or willing to be vaccinated), into a 2/3 training set (n=4935 with 91.3% willing to vaccinate) and a 1/3 different hold-out set to verify model performance (n=2467 with 91.3% willing to vaccinate). For the machine learning models, categorical question and answer combinations from the survey and demographic variables, including gender, age, body mass index (BMI), race, income and education, were One-Hot encoded (i.e. converted to dummy variables). This resulted in a total of 85 features (Supplement S2) that were used for the construction of the Random Forest. The model was tuned with respect to terminal node size and mtry (number of features available for splitting at each tree node), with class imbalance being addressed using stratified re-sampling for each of the 4001 trees. The most relevant features were determined using a recursive feature elimination approach. Starting with a model trained using the complete set of features, normalized permutation importance scores were determined and the bottom 4% of features were removed. The resulting model with all features (n=85) or the recursively reduced models were evaluated using the hold-out dataset. The model with the minimum set of features was selected based on maintaining a high balanced accuracy on the hold-out dataset (i.e., the average of specificity and sensitivity), compared to the full model. Shortly after the November survey was offered, Pfizer announced a first interim analysis reporting >90% efficacy of their vaccine candidate on November 9, 2020. 14 We investigated if that news had an impact on willingness to vaccinate in our population and compared those who answered the survey before the 9 th to those who answered after (excluding those who answered on the 9 th itself) using an ordered logistic regression model with four-level willingness to be vaccinated as the outcome and an indicator variable for the time period (before and after November 9 th ) and gender as predictors. Statistical analyses were performed using R (3.5.1 and 3.6.1) and r-packages randomForest (4.6-14) 15 , caret (6.0-84) 16 and MASS (7.3-53). 17 Data analyses was performed by JN, MK and GJW. The assessment was offered to 9,106 participants with 7,621 (83.6%) completing the survey. Excluding participants (n=219) missing demographic data left 7,402 participants (81.3%) for the study analyses (Table 1) . Overall, 63.6% of participants reported they were very willing to receive a COVID-19 vaccine, 27.8% were somewhat willing, 6.0% were not very willing, and 2.6% were not at all willing. Treated as a dichotomous response, 91.3% were considered "willing" to be immunized while 8.7% were "unwilling" (Table 1) . All rights reserved. No reuse allowed without permission. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted January 11, 2021. ; https://doi.org/10.1101/2021.01.10.20248831 doi: medRxiv preprint Figure 1 shows results of univariable evaluations of demographic factors associated with vaccine willingness. Black or African American race was most strongly associated with decreased odds of vaccine willingness (odds ratio 0.24, 95% CI 0.18 -0.31) (Figure 1 ). A total of 26.8% of Black or African American participants noted they were not very willing or not at all willing to vaccinate, compared with 8.0% of white participants (Table 1) . Women were also less willing to be vaccinated as shown in Table 1 by 12.1 % of women and 5.7% of men being not very or not at all willing to vaccinate against COVID-19 (odds ratio 0.49, 95% CI 0.45 -0.54) ( Figure 1 ). Income and education are also associated with willingness to be vaccinated, with higher income and higher education being associated with a higher willingness to be vaccinated ( Figure 1 ). Surveyed beliefs about COVID-19 and the COVID-19 vaccine (Figure 2 ), as well as beliefs about vaccines in general (Supplemental S3), were found to be strongly associated with willingness to vaccinate. Regarding COVID-19, the most strongly associated beliefs included that the COVID-19 vaccine will help protect "myself and others" (odds ratio 38.6, 95% CI 32.4 -46.1), the COVID-19 vaccine would be safe and effective (odds ratio 21.6, 95% CI 18.9 -24.7), and being comfortable with short term side effects such as prolonged injection site pain (odds ratio 10.9, 95% CI 9.1 -13.1). These beliefs were consistently important across participants who were White, Asian, African American or Black (Supplemental S4). The vast majority of those who would be willing to vaccinate indicated they would talk to their healthcare provider (HCP) or staff before deciding whether or not to receive the vaccine (91.4% of women and 88.9% of men) (Supplement S5). The majority of those who indicated All rights reserved. No reuse allowed without permission. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted January 11, 2021. ; https://doi.org/10.1101/2021.01.10.20248831 doi: medRxiv preprint they would not be willing to be vaccinated (68.4% of women and 62.3% of men) also indicated they would talk to their healthcare provider before deciding (Supplement S5). Specifically, we categorized the proportions of those who would talk to their HCP before deciding among those not at all willing and not very willing, by gender and race ( To identify a set of determinants that separate those who are willing and unwilling to be vaccinated, we constructed a Random Forest classification algorithm. From the survey and the available self-reported demographic data, we extracted a list of features (Supplemental S2, S5) to be used in the first model. This initial model using all 85 features resulted in 90.2% balanced accuracy (average of 90.7% sensitivity and 89.7% specificity) when applied to the hold-out dataset. When testing the recursively reduced models, the balanced accuracy remained near constant up to the model with 9 remaining features (89.5% balanced accuracy with 87.4% sensitivity and 91.6% specificity). A further reduction (removing the least important feature from the set of 9) resulted in a 12.3 percent point reduction in balanced accuracy primarily due to misclassification of the not willing to vaccinate (Specificity = 55.6%). The features coming out of our model ( Figure 3 ) revealed five main indicators: belief whether the COVID-19 vaccine would be safe and effective, belief whether a COVID-19 vaccine would help protect "myself and others," degree of comfort with potential short term side effects 1 0 from a COVID-19 vaccine, the belief whether vaccines in general are safe and important, and whether the respondent was Black or African American. Willingness to vaccinate increased after November 9 th when results of the Pfizer phase 3 vaccine trial were released (odds ratio 1.46, 95% CI 1.28 -1.69, Supplemental S6). Prior to that date, 2.8% of adults were not at all willing to receive a COVID-19 vaccine and 6.4% were "not very" willing; after this these decreased to 1.7% and 5.7%, respectively. The recent approval of vaccines for COVID-19 has increased the focus on the need to maximize public vaccine acceptance. Vaccine uptake in older adults is of particular importance as increasing age is the leading risk factor for mortality and complications from COVID-19 infections. 12 In this large survey of adults age 65 and older conducted in the United States in November 2020, the vast majority (91%) of adults reported that they are willing to receive a COVID-19 vaccine. However, even in this population of people with sufficient health literacy and trust in the healthcare system to participate in a digital clinical trial, 1 in 11 reported unwillingness to receive a vaccine. More concerningly, rates of vaccine unwillingness were higher in Black or African American adults and those at lower income and education levels, suggesting the potential for uneven vaccine uptake in at-risk communities. In this study, Black or African American race was the only factor associated with willingness to immunize after accounting for beliefs about the vaccine; 1 in 4 Black or African American participants reported unwillingness to receive a vaccine. This is slightly lower than 1 1 previous reports of ~40% unwilling, 8,19,20 but is consistent with other studies that show that willingness among Black or African Americans is improving. 7 We also found lower rates of reported vaccine willingness in women compared with men, a factor that has been shown in other studies. 11,19 Socioeconomic factors, including higher education and higher income, were also associated with increased reported willingness to be vaccinated. Notably, these findings contrast with characteristics of adults who refuse vaccines for their children. In studies of vaccine exemptions, higher income and education are often associated with higher rates of vaccine refusal. 18 Given that lower income communities and communities of color are at higher risk of COVID-19, vaccine hesitancy in these groups is of particular concern. Even if overall vaccine uptake is high, clustering of unimmunized persons can lead to continued circulation of vaccine-preventable diseases. 21 The strongest factors associated with and indicative of vaccine willingness in this population were beliefs about the COVID-19 vaccine's safety and efficacy, and a more altruistic belief whether a COVID-19 vaccine will help protect "myself and others." Among those disinclined to vaccinate, the majority stated that they would discuss their decision with their healthcare provider, providing an important opportunity for education. Despite differences in rates of vaccine willingness by gender and race, the associations between beliefs about a COVID-19 vaccine and reported willingness to receive a vaccine were consistent across subgroups. In addition to broader public education campaigns about COVID-19, specific efforts should be made to facilitate healthcare patient-provider communication about COVID-19 vaccine focused on vaccine safety and efficacy. While the study was not designed to determine the impact of vaccine-related news, the release of results from Pfizer's Phase 3 vaccine trial occurring in the middle of the survey All rights reserved. No reuse allowed without permission. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted January 11, 2021. ; https://doi.org/10.1101/2021.01.10.20248831 doi: medRxiv preprint provided an opportunity to evaluate the impact of positive vaccine news on vaccine attitudes. Increased vaccine willingness was seen after the trial results were released, suggesting that public willingness to vaccinate may continue to rise as additional positive data are released. On the other hand, given the potential for vaccine related data to shift perception, there remains the possibility that negative news stories about the vaccine (including reports of adverse events) may negatively impact vaccine willingness. The high willingness among participants in our population to be vaccinated is similar to that reported in other assessments in this age group. Recently reported results from the Kaiser Family Foundation found that 85% of those 65 and older were willing to receive a vaccine. 8 Older adults consistently express a higher willingness to accept a COVID-19 vaccine than younger populations. 3, 5, 6, 11 Reasons for this may include a higher perceived risk of COVID-19 illness compared to younger adults, prior experience with vaccine preventable diseases and mass vaccination campaigns for diseases such as polio, or comfort with routine immunizations due to being recommended for influenza vaccine. This study demonstrates the power of the digital platform used in the Heartline TM Study to rapidly generate real-world data. There are key features of this platform that enable rapid data generation: a properly constructed informed consent form that permits ad hoc survey deployment for data collection; a mobile app capable of pushing content and gathering variable but structured data; a back-end data structure that enables rapid analysis; and an app design that keeps participants highly engaged throughout the entire study, as evidenced by 83.6% of participants who took the survey. This platform opens the possibility of studies that investigate multiple effects over time or serial interventions in a population. 1 3 These findings should be interpreted in the context of several potential limitations. There is an inherent bias that comes with studying populations who have chosen to enroll into a clinical study. Heartline TM participants have less representation of Black or African American and Asians compared to the general U.S. 65+ population and skew higher in education and income, which may have led to an overestimate of vaccine acceptance compared with the general population. Nevertheless, finding that 1 in 11 patients in this selected group are unwilling to be vaccinated may portend even lower rates in a broader population. Next, our analysis of the impact of vaccine-related news occurred during a time period when infections continued to rise; whether changes in attitudes were due to vaccine news or due to other factors is unclear. Finally, we asked about vaccine willingness, which may not directly translate into behavior, particularly if attitudes shift over time. We also highlight several strengths, including a high response rate (>80%), a short period of data collection (2 weeks), and the ability to deploy the survey rapidly in response to the pandemic. In a 65 and older U.S. population, most are willing to be vaccinated, with Black or African American participants and females significantly less willing. The majority would be willing to discuss their concerns with their providers, who could leverage the beliefs identified here in tailoring a message to encourage vaccination. Developing implementable strategies to consistently communicate the potential benefits of vaccination could improve acceptance and help speed the efforts to thwart this global pandemic. The Heartline TM Study is supported by Johnson & Johnson and Apple. Apple neither supported nor participated in survey development or interpretation for this article. All rights reserved. No reuse allowed without permission. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted January 11, 2021. 14. Pfizer and BioNTech announce vaccine candidate against COVID-19 achieved success in first interim analysis from Phase 3 study. November 9, 2020. https://www.pfizer.com/news/press-release/press-release-detail/pfizer-and-biontechannounce-vaccine-candidate-against (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. Plus-minus values are means ± standard deviations (SD). Overall column percentages represent % of overall sample (column percent). Percentages in willing and unwilling columns represent row %. † The body-mass index is the weight in kilograms divided by the square of the height in meters. ‡ Race was reported by the participants, who could select more than one category. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. 1 8 s h o r t t e r m s i d e e f f e c t s s u c h a s s t o m a c h p a i n o r n a u s e a i f t h e v a c c i n e e f f i c i e n t l y p r e v e n t s C O V I D -1 9 . ' are 3.0 times more likely to be more willing as compared to those who selected 'neutral' All rights reserved. No reuse allowed without permission. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted January 11, 2021. ; https://doi.org/10.1101/2021.01.10.20248831 doi: medRxiv preprint Table 1 . Demographics of the participants completing the vaccine assessment All rights reserved. No reuse allowed without permission. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The body-mass index is the weight in kilograms divided by the square of the height in meters. ‡ Race was reported by the participants, who could select more than one category. All rights reserved. No reuse allowed without permission. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted January 11, 2021. ; https://doi.org/10.1101/2021.01.10.20248831 doi: medRxiv preprint 1 All rights reserved. No reuse allowed without permission. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted January 11, 2021. ; https://doi.org/10.1101/2021.01.10.20248831 doi: medRxiv preprint All rights reserved. No reuse allowed without permission. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted January 11, 2021. ; https://doi.org/10.1101/2021.01.10.20248831 doi: medRxiv preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted January 11, 2021. ; https://doi.org/10.1101/2021.01.10.20248831 doi: medRxiv preprint I w o u l d t a l k t o m y h e a l t h c a r e p r o v i d e r w h e n c o n s i d e r i n g a C O V I D -1 9 v a c c i n e , b e f o r e d e c i d i n g w h e t h e r o r n o t t o r e c e i v e t h e v a c c i n All rights reserved. No reuse allowed without permission. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted January 11, 2021. Table S6 : Impact of positive vaccine efficacy news by level of willing to vaccinate November 9, 2020, Pfizer announced a first interim analysis reporting >90% efficacy of their vaccine candidate. The impact of this news on willingness was evaluated among those who answered the survey before the 9th to those who answered thereafter (excluding those who answered on the 9th itself). Those after November 9th were more willing to vaccinate (odds ratio 1.46, 95%CI 1.28 -1.69). All rights reserved. No reuse allowed without permission. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted January 11, 2021. ; https://doi.org/10.1101/2021.01.10.20248831 doi: medRxiv preprint I a m c o n c e r n e d a C O V I D -1 9 v a c c i n e w i l l h a v e s i d e e f f e c t s . D i s a g r e e , N e u t r a l , A g r e e 3 I a m c o n c e r n e d m y i n s u r a n c e w i l l n o t c o v e r a C O V I D -1 9 v a c c i n e . D i s a g r e e , N e u t r a l , A g r e e 3 I a m c o n c e r n e d a b o u t r e c e i v i n g a C O V I D -1 9 v a c c i n e b e c a u s e I a m a f r a i d o f n e e d l e s D i s a g r e e , N e u t r a l , A g r e e 3 I a m c o m f o r t a b l e t a k i n g a C O V I D -1 9 v a c c i n e t h a t h a s s h o r t t e r m s i d e e f f e c t s s u c h a s p r o l o n g e d i n j e c t i o n s i t e p a i n ( e . g . , r e d n e s s o r s w e l l i n g ) i f t h e v a c c i n e e f f i c i e n t l y p r e v e n t s C O V I D -1 9 . D i s a g r e e , N e u t r a l , A g r e e 3 I a m c o m f o r t a b l e t a k i n g a C O V I D -1 9 v a c c i n e t h a t h a s s h o r t t e r m s i d e e f f e c t s s u c h a s m o d e r a t e f e v e r ( > 3 8 d e g r e e s c e l s i u s o r > 1 0 0 d e g r e e s F a h r e n h e i t ) i f t h e v a c c i n e e f f i c i e n t l y p r e v e n t s C O V I D -1 9 . D i s a g r e e , N e u t r a l , A g r e e 3 I a m c o m f o r t a b l e t a k i n g a C O V I D -1 9 v a c c i n e t h a t h a s s h o r t t e r m s i d e e f f e c t s s u c h a s s t o m a c h p a i n o r n a u s e a i f t h e v a c c i n e e f f i c i e n t l y p r e v e n t s C O V I D -1 All rights reserved. No reuse allowed without permission. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted January 11, 2021. ; https://doi.org/10.1101/2021.01.10.20248831 doi: medRxiv preprint Figure S3 : Forest plot of willingness to vaccinate by survey response (general vaccine beliefs) Shown are Odds Ratios (95% CI) for willingness to vaccinate. Odds Ratios were calculated using ordered logistic regression model with the 4 levels of willingness to be vaccinated as the outcome while adjusting for gender and race. All rights reserved. No reuse allowed without permission. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted January 11, 2021. ; https://doi.org/10.1101/2021.01.10.20248831 doi: medRxiv preprint Figure S4 : Forest plots of willingness to vaccinate by COVID-19 beliefs and race Shown are Odds Ratios (95% CI) for willingness to vaccinate for the survey by race: White (A), Asian (B), and Black (C). Odds Ratios were calculated using ordered logistic regression model with the 4 levels of willingness to be vaccinated as the outcome while adjusting for gender and race. Reference for each survey question is the option 'neutral' and is indicated by an open circle. na indicates insufficient subjects for this category. All rights reserved. No reuse allowed without permission. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted January 11, 2021. ; https://doi.org/10.1101/2021.01.10.20248831 doi: medRxiv preprint 1 All rights reserved. No reuse allowed without permission. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted January 11, 2021. ; https://doi.org/10.1101/2021.01.10.20248831 doi: medRxiv preprint All rights reserved. No reuse allowed without permission. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted January 11, 2021. ; https://doi.org/10.1101/2021.01.10.20248831 doi: medRxiv preprint Table S6 : Impact of positive vaccine efficacy news by level of willing to vaccinate November 9, 2020, Pfizer announced a first interim analysis reporting >90% efficacy of their vaccine candidate. The impact of this news on willingness was evaluated among those who answered the survey before the 9th to those who answered thereafter (excluding those who answered on the 9th itself). Those after November 9th were more willing to vaccinate (odds ratio 1.46, 95%CI 1.28 -1.69). All rights reserved. No reuse allowed without permission. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted January 11, 2021. ; https://doi.org/10.1101/2021.01.10.20248831 doi: medRxiv preprint When will we have a vaccine?" -Understanding questions and answers about Covid-19 vaccination Vaccine communication in the age of COVID-19: Getting ready for an information war Just 50% of Americans plan to get a Covid-19 vaccine. Here's how to win over the rest The share of Americans interested in getting COVID-19 vaccine as soon as possible is dropping More Americans now willing to get COVID-19 vaccine A global survey of potential acceptance of a COVID-19 vaccine Axios-Ipsos poll: Vaccine resistance grows. Axios