Int J Biol Sci 2021; 17(6):1461-1468. doi:10.7150/ijbs.59170 This issue


Review of Covid-19 vaccine clinical trials - A puzzle with missing pieces

Hang Fai Kwok

Institute of Translational Medicine, Faculty of Health Sciences, University of Macau, Avenida de Universidade, Taipa, Macau SAR

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Kwok HF. Review of Covid-19 vaccine clinical trials - A puzzle with missing pieces. Int J Biol Sci 2021; 17(6):1461-1468. doi:10.7150/ijbs.59170. Available from

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Graphic abstract

A year after the initial outbreak of Covid-19 pandemic, several Phase III clinical trials investigating vaccine safety and efficacy have been published. These vaccine candidates were developed by different research groups and pharmaceutical companies with various vaccine technologies including mRNA, recombinant protein, adenoviral vector and inactivated virus-based platforms. Despite numerous successful clinical trials, participants enrolled in these trials are limited by trial inclusion and exclusion criteria, geographic location and viral outbreak situation. Many questions still remain, especially for specific subgroups, including the elderly, females with pregnancy and breastfeeding status, and adolescents. At the same time, vaccine efficacy towards asymptomatic infection and specific viral variants are still largely unknown. This review will cover vaccine candidates with Phase III clinical trial data released and discuss the scientific data available so far for these vaccine candidates for different subgroups of people and different viral variants.

Keywords: SARS-CoV-2, Pandemic, Vaccination, Different subgroups, Viral Variants