Marike Andreas, Claire Iannizzi, Emma Bohndorf, Ina Monsef, Vanessa Piechotta, Joerg J Meerpohl, Nicole Skoetz

Vaccines are effective in preventing severe COVID-19, a disease for which few treatments are available and which can lead to disability or death. Widespread vaccination against COVID-19 may help protect those not yet able to get vaccinated. In addition, new and vaccine-resistant mutations of SARS-CoV-2 may be less likely to develop if the spread of COVID-19 is limited. Different vaccines are now widely available in many settings. However, vaccine hesitancy is a serious threat to the goal of nationwide vaccination in many countries and poses a substantial threat to population health. This scoping review maps interventions aimed at increasing COVID-19 vaccine uptake and decreasing COVID-19 vaccine hesitancy.  OBJECTIVES: To scope the existing research landscape on interventions to enhance the willingness of different populations to be vaccinated against COVID-19, increase COVID-19 vaccine uptake, or decrease COVID-19 vaccine hesitancy, and to map the evidence according to addressed populations and intervention categories.   SEARCH METHODS: We searched Cochrane COVID-19 Study Register, Web of Science (Science Citation Index Expanded and Emerging Sources Citation Index), WHO COVID-19 Global literature on coronavirus disease, PsycINFO, and CINAHL to 11 October 2021.  SELECTION CRITERIA: We included studies that assess the impact of interventions implemented to enhance the willingness of different populations to be vaccinated against COVID-19, increase vaccine uptake, or decrease COVID-19 vaccine hesitancy. We included randomised controlled trials (RCTs), non-randomised studies of intervention (NRSIs), observational studies and case studies with more than 100 participants. Furthermore, we included systematic reviews and meta-analyses. We did not limit the scope of the review to a specific population or to specific outcomes assessed. We excluded interventions addressing hesitancy towards vaccines for diseases other than COVID-19. Data were analysed according to a protocol uploaded to the Open Science Framework. We used an interactive scoping map to visualise the results of our scoping review. We mapped the identified interventions according to pre-specified intervention categories, that were adapted to better fit the evidence. The intervention categories were: communication interventions, policy interventions, educational interventions, incentives (both financial and non-financial), interventions to improve access, and multidimensional interventions. The study outcomes were also included in the mapping. Furthermore, we mapped the country in which the study was conducted, the addressed population, and whether the design was randomised-controlled or not.  MAIN RESULTS: We included 96 studies in the scoping review, 35 of which are ongoing and 61 studies with published results. We did not identify any relevant systematic reviews. For an overview, please see thehttps://egmopenaccess.3ieimpact.org/evidence-maps/interventions-increase-covid-19-vaccine-uptake?type=share https://egmopenaccess.3ieimpact.org/evidence-maps/interventions-increase-covid-19-vaccine-uptake?type=share.   Studies with published results Of the 61 studies with published results, 46 studies were RCTs and 15 NRSIs. The interventions investigated in the studies were heterogeneous with most studies testing communication strategies to enhance COVID-19 vaccine uptake. Most studies assessed the willingness to get vaccinated as an outcome. The majority of studies were conducted in English-speaking high-income countries. Moreover, most studies investigated digital interventions in an online setting. Populations that were addressed were diverse. For example, studies targeted healthcare workers, ethnic minorities in the USA, students, soldiers, at-risk patients, or the general population.  Ongoing studies Of the 35 ongoing studies, 29 studies are RCTs and six NRSIs. Educational and communication interventions were the most used types of interventions. The majority of ongoing studies plan to assess vaccine uptake as an outcome. Again, the majority of studies are being conducted in English-speaking high-income countries. In contrast to the studies with published results, most ongoing studies will not be conducted online. Addressed populations range from minority populations in the USA to healthcare workers or students. Eleven ongoing studies have estimated completion dates in 2022.   AUTHORS' CONCLUSIONS: We were able to identify and map a variety of heterogeneous interventions for increasing COVID-19 vaccine uptake or decreasing vaccine hesitancy. Our results demonstrate that this is an active field of research with 61 published studies and 35 studies still ongoing. This review gives a comprehensive overview of interventions to increase COVID-19 vaccine uptake and can be the foundation for subsequent systematic reviews on the effectiveness of interventions to increase COVID-19 vaccine uptake.  A research gap was shown for studies conducted in low and middle-income countries and studies investigating policy interventions and improved access, as well as for interventions addressing children and adolescents. As COVID-19 vaccines become more widely available, these populations and interventions should not be neglected in research.