Abstract
The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants and the waning of vaccine-elicited neutralizing antibodies suggests that additional coronavirus disease 2019 (COVID-19) vaccine doses may be needed for individuals who initially received CoronaVac. We evaluated the safety and immunogenicity of the recombinant adenovirus type 5 (AD5)-vectored COVID-19 vaccine Convidecia as a heterologous booster versus those of CoronaVac as homologous booster in adults previously vaccinated with CoronaVac in an ongoing, randomized, observer-blinded, parallel-controlled phase 4 trial (NCT04892459). Adults who had received two doses of CoronaVac in the past 3–6 months were vaccinated with Convidecia (n = 96) or CoronaVac (n = 102). Adults who had received one dose of CoronaVac in the past 1–3 months were also vaccinated with Convidecia (n = 51) or CoronaVac (n = 50). The co-primary endpoints were the occurrence of adverse reactions within 28 d after vaccination and geometric mean titers (GMTs) of neutralizing antibodies against live wild-type SARS-CoV-2 virus at 14 d after booster vaccination. Adverse reactions after vaccination were significantly more frequent in Convidecia recipients but were generally mild to moderate in all treatment groups. Heterologous boosting with Convidecia elicited significantly increased GMTs of neutralizing antibody against SARS-CoV-2 than homologous boosting with CoronaVac in participants who had previously received one or two doses of CoronaVac. These data suggest that heterologous boosting with Convidecia following initial vaccination with CoronaVac is safe and more immunogenic than homologous boosting.
Highlights
The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants and the waning of vaccine-elicited neutralizing antibodies suggests that additional coronavirus disease 2019 (COVID-19) vaccine doses may be needed for individuals who initially received CoronaVac
The combination of heterologous prime–boost schedules with inactivated vaccines and adenovirus-based vaccines such as adenovirus type 5 (AD5)-nCOV, ChAdOx1 nCoV19 or Ad26.COV2.S could potentially enhance the feasibility of vaccine distribution, for some low- or middle-resource countries with limited or unpredictable CoronaVac supplies to allow for three doses per individual
Participants in the three-dose regimen cohort were randomized at a 1:1 ratio to receive a third dose of Convidecia or CoronaVac
Summary
The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants and the waning of vaccine-elicited neutralizing antibodies suggests that additional coronavirus disease 2019 (COVID-19) vaccine doses may be needed for individuals who initially received CoronaVac. We evaluated the safety and immunogenicity of the recombinant adenovirus type 5 (AD5)-vectored COVID-19 vaccine Convidecia as a heterologous booster versus those of CoronaVac as homologous booster in adults previously vaccinated with CoronaVac in an ongoing, randomized, observer-blinded, parallel-controlled phase 4 trial (NCT04892459). The emergence of SARS-CoV-2 variants with increased infectivity and transmissibility and the waning of neutralizing antibodies elicited by the inactivated vaccine might lead to lower vaccine protection[6]. Heterologous schedules incorporating COVID-19 vaccines across different platforms may promote antibody affinity maturation and influence the breadth of vaccine-elicited neutralizing antibodies by including different antigens, types of vectors, delivery routes, doses and/or adjuvants at different times[9,10]. We report the safety and immunogenicity of initial vaccination with one or two doses of Nature Medicine | www.nature.com/naturemedicine
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