In August 2020, the first trial assessing an inactivated COVID-19 vaccine was published 
In August 2020, the first trial assessing an inactivated COVID-19 vaccine was published . in streamlining future global responses to the pandemic. strong class=”kwd-title” Keywords: COVID-19, SARS-COV-2, vaccines, clinical trials L-Leucine 1. Introduction The COVID-19 pandemic continues to spread across much of the world, despite efforts by individuals and governments to curb transmission of the virus . Medical systems in multiple developed nations have been pushed to their limits, overwhelming healthcare workers and depleting resources [2,3]. Consequently, an international collaborative effort between governments, academic research institutions, and private companies was launched during the early stages of the pandemic to develop vaccines with unprecedented rapidity . By 28 November 2020, clinical trials of nine promising COVID-19 vaccines (chosen for further phase 3 trials or development) have been published in high-profile medical and scientific journals [5,6,7,8,9,10,11,12,13,14]. The purpose of these early trials has been to establish safety, but also to demonstrate some degree of immunogenicity. Large investments have been made to expedite availability of promising vaccine candidates to the public through rapid initiation of phase 3 trials and manufacturing of large amounts of vaccine product prior to determination of vaccine effectiveness. Generous L-Leucine funding of COVID-19 vaccines permitted the use of novel vaccine platforms, many of which made use of rapidly available sequencing information to develop products more quickly than traditional approaches which require growth of virus in biosafety level 3 facilities. While the scientific and regulatory communities are eagerly awaiting the results of phase 3 efficacy trials before approval of vaccines, some have advocated advancing vaccine candidates to market prematurely. In the face of this pressure, a critical comparison of available phase 1/2 study data was performed. 2. COVID-19 Vaccine Candidates Starting on 5 May 2020, the first phase 1 clinical trial evaluating a non-replicating adenovirus type-5 (Ad5) vaccine was published (Table 1) . This was followed by a phase 2 study in July 2020 . Two more trials were published in July 2020 demonstrating safety and immunogenicity of an mRNA vaccine platform (mRNA-1273) and a chimpanzee adenovirus-vectored vaccine (ChAdOx1 nCoV-19) [6,8]. In August 2020, the first trial assessing an inactivated COVID-19 vaccine was published . Following this study, two more were published L-Leucine in September 2020: a recombinant SARS-COV-2 nanoparticle full-length S protein vaccine (NVX-CoV2373) and a combination recombinant adenovirus 26 (rAd26) and rAd5, named Gam-COVID-Vac [10,11]. Data on two additional mRNA vaccines (BNT162b2 and BNT162b1) were published on 13 October with BNT162b2 chosen to progress to stage 3 trials , though data on BNT162b1 had been already published earlier [15,16]. Since BNT162b1 is not planned to undergo phase 3 trials, it was not included in the comparison tables in this review. Then, on 15 October, phase 1 and 2 data were published demonstrating safety and immunogenicity of another inactivated virus vaccine (BBIBP-CorV) . Most recently, a phase 1/2 study assessing the efficacy of another inactivated, aluminum hydroxide-adjuvanted vaccine candidate (CoronaVac) was published , while other early phase clinical trial manuscripts like Janssen/Johnson & Johnsons adenovirus 26 based vector vaccine (Ad26.COV2.S) , CureVacs mRNA-based vaccine (CVnCoV) , and Medicagos virus-like particle vaccine are available in preprint . These have not been included in the tables or analysis in this review and are likely to be joined in the coming L-Leucine months by many other vaccine candidates in current early clinical trials. Table 1 Characteristics of COVID-19 vaccine candidates and phase 1 or 2 2 clinical Rabbit polyclonal to CD80 trials. thead th align=”center” valign=”middle” style=”border-top:solid thin;border-bottom:solid thin” rowspan=”1″ colspan=”1″ /th th align=”center” valign=”middle” style=”border-top:solid thin;border-bottom:solid.