Evidence before this study
infection
INFECTION, VIRUS, SECONDARY
Many low-income and middle-income countries use inactivated COVID-19 vaccines in their existing vaccination programmes, and the use of these vaccines has been proposed in high-income countries; however, data comparing inactivated vaccine efficacy with other vaccine platforms are scarce. We searched PubMed and Web of Science for publications between Jan 1, 2019, and June 22, 2023, with the following search strategy and no restriction on language nor publication type: “((covid) OR (sars-cov-2)) AND (((inactivated vaccine) OR (coronavac) OR (sinovac) OR (BIBP) OR (BBIBP) OR (sinopharm)) AND ((booster) OR (third)) AND (((randomised) OR (randomized)) AND (trial)))”. Included within the 55 identified articles were six randomised trials on heterologous COVID-19 vaccination using inactivated vaccines and mRNA vaccines, including three that studied homologous versus heterologous third-dose (booster) vaccination and included live virus neutralising antibodies as primary or secondary outcomes. These three studies compared third-dose heterologous mRNA vaccination to homologous inactivated vaccination after two doses (primary series) of inactivated vaccines, and suggested third-dose heterologous mRNA vaccination led to higher neutralising antibody response. Only one of the studies also included an efficacy outcome (ie, infection), and showed a relative vaccine efficacy of 38% against symptomatic clinical cases with lower risk of infection in the heterologous mRNA vaccination group. None of the six identified randomised trials included comparisons between third-dose mRNA and inactivated vaccine after a primary series of mRNA vaccination.