COVID-19 is a global pandemic with no effective therapeutic and preventive agents. Given the high infectivity of the SARS-CoV-2 and severity of the disease, vaccines are urgently needed to tackle the infection of this novel coronavirus. Thus far, various types of vaccine candidates, in different stages of preclinical testing and clinical trials, are being explored, including RNA- and DNA-based, vectored and attenuated virus, and recombinant proteins. However, possible adverse effects and limitations exist.