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Objectives: This study aimed to comprehensively outline the methodological approaches used in published research comparing the vaccine effectiveness (VE) of coronavirus disease 2019 (COVID-19) vaccines. Methods: A systematic search was conducted on June 13, 2024, to identify comparative studies evaluating the effectiveness of mRNA versus non-mRNA and monovalent versus bivalent COVID-19 vaccines. We screened titles, abstracts, and full texts, collecting data on publication year, country, sample size, study population composition, study design, VE estimates, outcomes, and covariates. Studies that reported relative VE (rVE) were analyzed separately from those that did not. Results: We identified 25 articles comparing rVE between mRNA and non-mRNA COVID-19 vaccines, as well as between monovalent and bivalent formulations. Among the studies assessing VE by vaccine type, 126 did not provide rVE estimates. Comparative VE studies frequently employed retrospective cohort designs. Among the definitions of rVE used, the most common were hazard ratio and absolute VE, calculated as (1-odds ratio)×100. Studies were most frequently conducted in the United Kingdom and the United States, and the most common outcome was infection. Most targeted the general population and assessed the VE of mRNA vaccines using the AstraZeneca vaccine as a reference. A small proportion, 7.3% (n=11), did not adjust for any variables. Only 3 studies (2.0%) adjusted for all core confounding variables recommended by the World Health Organization. Conclusion: Few comparative studies of COVID-19 vaccines have incorporated rVE methodologies. Reporting rVE and employing a consistent set of covariates can broaden our understanding of COVID-19 vaccines. [ABSTRACT FROM AUTHOR]

The variant B.1.1.7 of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the RNA virus causing the pandemic more than a year worldwide, was reported from United Kingdom (UK) in late December 2020. It was reported that mortality increases by 65% and transmissibility increases by 70%, which may result in an increase of reproduction number to 1.13-1.55 from 0.75-0.85. To analyze the global increasing trend of the variant B.1.1.7, we extracted results of B.1.1.7 from GISAID on May 11 and May 12, 2021, and conducted a dose-response regression. It took 47 days to reach 20% and 121 days to reach 50% among the sequence submitted from UK. In Korea, cases of B.1.1.7 have increased since the first report of three cases on December 28, 2020. Positive rate of B.1.1.7 in Korea was 21.6% in the week from May 9 to May 15, 2021. Detection rate of the variants is expected to increase further and new variants of SARS-CoV-2 are emerging, so a close monitoring and control would be maintained for months. [ABSTRACT FROM AUTHOR]