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

Abstract

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 to 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. 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.Findings: 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 Interpretation: Although the short-term reactogenicity with the heterologous regimen was higher than with the homologous regimes, other factors such as higher efficacy and limited resources during the pandemic may prevail in recommending specific regimens.Funding: Bavarian Ministry of Science and Art.Declaration of Interest: LW, NL own(ed) stocks of BioNTech, the investments were made before being involved in the project. The other authors declare not to have any conflict of interests.Ethical Approval: The Ethics Committee of the Friedrich Alexander University approved the study (47_21 B, 01.03.2021 and 161_21 B, 12.05.2021). All participants consented to participate.