Reactogenicity After Heterologous and Homologous COVID-19 Prime-Boost Vaccination Regimens: Descriptive Interim Results of a Comparative Observational Cohort Study

Background: Due to safety signals after vaccination with COVID-19 vector vaccines, several states recommended complete the primary immunization series in individuals having received one dose of ChAdOx1 (AstraZeneca) an mRNA vaccine. However, data on and reactogenicity this heterologous regimen are still scarce. The aim study was therefore compare frequency medical consultations boost a mRNA-vaccines (BNT162b2, BioNTech/Pfizer or mRNA-1273, Moderna) homologous regimens mRNA-vaccines, respectively. Methods: In observational cohort were assessed 14 19 days (short-term) 40 56 (long-term) using web-based surveys. short-term survey solicited unsolicited reactions assessed. long-term focussed health problems leading consultation vaccination, including those that not suspected be vaccine-related. Findings: total, 9146 participants completed at least surveys (ChAdOx1/ChAdOx1: n = 552, ChAdOx1/mRNA: 2382, mRNA/mRNA: 6212). survey, 86 % ChAdOx1/mRNA reported reaction, ChAdOx1/ChAdOx1 mRNA/mRNA cohorts 58 76 %, respectively (age sex adjusted p < 0·0001). comparable proportions (ChAdOx1/ChAdOx1 vs. 15 18 16 age 0·398). Female gender associated higher more consultations. Younger reactogenicity, whereas elderly people consultations. Interpretation: Although than regimes, other factors such as efficacy limited resources during pandemic may prevail recommending specific regimens. Funding: Bavarian Ministry Science Art. Declaration Interest: LW, NL own(ed) stocks BioNTech, investments made before being involved project. authors declare have any conflict interests. Ethical Approval: Ethics Committee Friedrich Alexander University approved (47_21 B, 01.03.2021 161_21 12.05.2021). All consented participate.