BackgroundThe effectiveness of full Coronavirus Disease 2019 (COVID-19) vaccination against COVID-19 wanes over time. This study aimed to synthesize the clinical effectiveness of the first dose of COVID-19 booster by comparing it to the full vaccination.MethodsStudies in PubMed, Web of Science, Embase, and clinical trials databases were searched from 1 January 2021 to 10 September 2022. Studies were eligible if they comprised general adult participants who were not ever or currently infected with SARS-CoV-2, did not have impaired immunity or immunosuppression, and did not have severe diseases. The seroconversion rate of antibodies to S and S subunits and antibody titers of SARS-CoV-2, frequency, phenotype of specific T and B cells, and clinical events involving confirmed infection, admission to the intensive care unit (ICU), and death were compared between the first booster dose of COVID-19 vaccination group and full vaccination group. The DerSimonian and Laird random effects models were used to estimate the pooled risk ratios (RRs) and corresponding 95% confidence intervals (CIs) for the outcomes of clinical interest. While a qualitative description was mainly used to compare the immunogenicity between the first booster dose of COVID-19 vaccination group and full vaccination group. Sensitivity analysis was used to deal with heterogenicity.ResultsOf the 10,173 records identified, 10 studies were included for analysis. The first dose COVID-19 booster vaccine could induce higher seroconversion rates of antibodies against various SAS-CoV-2 fragments, higher neutralization antibody titers against various SARS-CoV-2 variants, and robust cellular immune response compared to the full vaccination. The risk of SARS-CoV-2 infection, the risk of admission to the ICU, and the risk of death were all higher in the non-booster group than those in the booster group, with RRs of 9.45 (95% CI 3.22–27.79; total evaluated population 12,422,454 vs. 8,441,368; I2 = 100%), 14.75 (95% CI 4.07–53.46; total evaluated population 12,048,224 vs. 7,291,644; I2 = 91%), and 13.63 (95% CI 4.72–39.36; total evaluated population 12,385,960 vs. 8,297,037; I2 = 85%), respectively.ConclusionA homogenous or heterogeneous booster COVID-19 vaccination could elicit strong humoral and cellular immune responses to SARS-CoV-2. Furthermore, it could significantly reduce the risk of SARS-CoV-2 infection and severe COVID-19 clinical events on top of two doses. Future studies are needed to investigate the long-term clinical effectiveness of the first booster dose of the COVID-19 vaccine and compare the effectiveness between homogenous and heterogeneous booster COVID-19 vaccination.Systematic review registrationhttps://inplasy.com/inplasy-2022-11-0114/, identifier: INPLASY2022110114.

Review question / Objective: To investigate the immune response and related clinical outcomes of healthy adults who received coronavirus vaccine booster compared with those who did not receive the vaccine booster. Condition being studied: The COVID-19 pandemic, which has spread since 2019, has created a huge disease and economic burden on the world. A large number of clinical trials have verified the effectiveness of COVID-19 vaccine. Previous studies have found that the serum conversion rate and antibody level of those vaccinated after the first two doses of COVID-19 vaccine continue to decrease, and the efficacy of the vaccine will decrease over time after the first two doses. Therefore, in order to maintain the protective efficacy of the vaccine, The need for a vaccine booster shot to achieve the expected goal of long-term effective prevention of the novel coronavirus has become a focus of discussion around the world.