ABSTRACT
Heterologous prime-boost vaccination is of increasing interest for COVID-19 vaccines. Evidence of rare thrombotic events associated with ChAdOx1-nCoV19 (Vaxzevria, ChAdOx) has lead several European countries to recommend a heterologous booster with mRNA vaccines for certain age groups (e.g. persons <60years in Germany), who have already received one dose of ChAdOx, although data on reactogenicity and safety of this vaccination regimen are still missing. Here we report reactogenicity data of homologous BNT162b2 (Comirnaty, BNT) or heterologous ChAdOx/BNT prime-boost immunisations in a prospective observational cohort study of 326 healthcare workers. Reactogenicity of heterologous ChAdOx/BNT booster vaccination was largely comparable to homologous BNT/BNT vaccination and overall well-tolerated. No major differences were observed in the frequency or severity of local reactions after either of the vaccinations. In contrast, notable differences between the regimens were observed for systemic reactions, which were most frequent after prime immunisation with ChAdOx (86%, 95CI: 79-91), and less frequent after homologous BNT/BNT (65%, 95CI: 56-72), or heterologous ChAdOx/BNT boosters (48%, 95CI: 36-59). This interim analysis supports the safety of currently recommended heterologous ChAdOx/BNT prime-boost immunisations with 12-week intervals.