7. Pioneers of COVID-19 vaccine program
Until February 9, 2021, 63 vaccine candidates to fight against SARS-CoV2 infection have entered clinical trials, while 179 candidates are going through preclinical developments [52] (Fig. 1). Among the vaccine candidates in clinical evaluation four inactivated, two protein subunit, four adenovirus- and two mRNA-based vaccines constitutes the leading candidates in the COVID-19 vaccine design scheme. Hereunto, only BNT162b2, mRNA-1273 (mRNA-based) along with BBIBP-CorV and CoronaVac (inactivated) vaccines have been emergency or conditionally approved in some countries and the other candidates were allowed for early or limited use [53] (Table 2).