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Background Due to safety signals after vaccination with COVID-19 vector vaccines, several states recommended to complete the primary immunization series in individuals having received one dose of ChAdOx1 (AstraZeneca) with an mRNA vaccine. However, data on safety and reactogenicity of this heterologous regimen are still scarce. The aim of this study was therefore to compare the reactogenicity and the frequency of medical consultations after boost vaccination in a heterologous regimen with ChAdOx1 and mRNA-vaccines (BNT162b2, BioNTech/Pfizer or mRNA-1273, Moderna) to homologous regimens with ChAdOx1 or mRNA-vaccines, respectively. Methods In an observational cohort study reactogenicity and safety were assessed 14–19 days (short-term) and 40 to 56 days (long-term) after the boost vaccination using web-based surveys. In the short-term survey solicited and unsolicited reactions were assessed, while the long-term survey focussed on health problems leading to medical consultation after the vaccination, including those that were not suspected to be vaccine-related. Results In total, 9146 participants completed at least one of the surveys (ChAdOx1/ChAdOx1: n = 552, ChAdOx1/mRNA: n = 2382, mRNA/mRNA: n = 6212). In the short-term survey, 86% with ChAdOx1/mRNA regimen reported at least one reaction, in the ChAdOx1/ChAdOx1 and mRNA/mRNA cohorts 58% and 76%, respectively (age and sex adjusted p < 0.0001). In the long-term survey, comparable proportions of individuals reported medical consultation (ChAdOx1/ChAdOx1 vs. ChAdOx1/mRNA vs. mRNA/mRNA: 15% vs. 18% vs. 16%, age and sex adjusted p = 0.398). Female gender was associated with a higher reactogenicity and more medical consultations. Younger age was associated with a higher reactogenicity, whereas elderly people reported more medical consultations. Conclusion Although the short-term reactogenicity was higher with the heterologous regimen than with the homologous regimens, other factors such as higher efficacy and limited resources during the pandemic may prevail in recommending specific regimens.

Background The Corona-Vakzin-Konsortium project (CoVaKo) analyses the efficacy and safety of COVID-19 vaccines in a real-world setting, as well as breakthrough infections in Bavaria, Germany. A subproject of CoVaKo aims to identify adverse reactions of the COVID-19 vaccine and compare these to adverse reactions of other vaccines in an online survey. In a preceding feasibility study, the study materials were tested for comprehensibility, visual design, and motivation to participate, as well as for their ability to be implemented and carried out in primary care practices and vaccination centres. Methods We used a mixed-methods research design. First, three focus groups consisting of general population participants were organised to evaluate the study materials and survey. Second, a test roll-out was conducted in vaccination centres and primary care practices that involved implementing and quantitatively evaluating the online survey. Third, interviews were conducted with participating general practitioners and heads of vaccination centres four weeks after the test roll-out. Results Parts of the information and registration form proved incomprehensible, specifically regarding the recruitment material and/or online survey. For example, headings were misleading given that, relative to other vaccinations, the COVID-19 vaccination was overemphasised in the title. Participants requested additional information regarding the procedure and completion time. Within 31 days, 2199 participants, who received either a COVID-19 vaccination (99%) or at least one of the control vaccinations (1%), registered for the study. Participants (strongly) agreed that the registration process was easy to understand, that the completion time was reasonable, and that the technical setup was straightforward. Physicians and heads of the vaccination centres perceived the study as easy to integrate into their workflow. The majority expressed willingness to participate in the main study. Conclusions Our study indicated that identifying and documenting adverse reactions following vaccinations using an online survey is feasible. Testing materials and surveys provided valuable insight, enabling subsequent improvements. Participation from health professionals proved essential in ensuring the practicality of procedures. Lastly, adapting the study’s organisation to external fluctuating structures and requirements confirmed necessary for a successful implementation, especially due to dynamic changes in the nation’s COVID-19 vaccination strategies. Trial registration The trial was retrospectively registered at the “Deutsches Register Klinischer Studien” (DRKS-ID: DRKS00025881) on Oct 14, 2021.

Background: The Corona-Vakzin-Konsortium project (CoVaKo) analyses the efficacy and safety of COVID-19 vaccines in a real-world setting and breakthrough infections in Bavaria, Germany. A subproject of CoVaKo aims to identify adverse events of the COVID-19 vaccine and to compare these to adverse events of other vaccines in an online survey. A prior feasibility study was conducted to test study materials for comprehensibility, visual design and motivation to participate and secondly, to test practical implementation and realization in primary care practices and vaccination centres.Methods: A mixed-methods design was used. Three focus groups with general population participants were performed to evaluate the study materials and survey. Second, a test-roll-out was conducted in vaccination centres and primary care practices, which involved implementation and quantitative evaluation of the online survey. Third, interviews were conducted with participating general practitioners and heads of vaccination centres four weeks after the test-roll-out.Results: Parts of the study information and registration form proved incomprehensible in the recruitment material and/or online survey. For example, headings were misleading since the COVID-19 vaccination was overemphasized in the title as compared to other vaccinations. Participants requested more information on the procedure and completion time. In 31 days, 2199 participants who received either a COVID-19 vaccination (99 %) or at least one of the control vaccinations (1 %) registered for the study. Participants (strongly) agreed that the registration process was easy to understand, that all relevant information was provided, the completion time was reasonable and technical framework manageable. Physicians and heads of the vaccination centres perceived the study as easy to integrate into their workflow and most of them were willing to participate in the main study.Conclusions: Our study indicated that capturing adverse events after vaccinations with an online survey is feasible. Testing of materials and surveys provided valuable improvements. Participation of health professionals is important to ensure practicality of the procedures. Flexible adaptation of the study organization to changing structures and requirements is necessary for a successful implementation, especially due to dynamic changes in COVID-19 vaccination strategies.Trial registration: The trial was retrospectively registered at “Deutsches Register Klinischer Studien” (DRKS-ID: DRKS00025881) on Oct 14, 2021.