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There is a strong consensus globally that production of an effective vaccine against SARS-CoV-2 is likely the most effective approach to sustainably controlling the COVID-19 pandemic. An unprecedented research effort and global coordination has resulted in a rapid development of vaccine candidates and initiation of trials. In this paper, we review vaccine candidate against COVID-19 and also challenges of vaccination have been explored in different region.

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Background: Severe acute respiratory system Cov-2 pandemic has affected the world populations for more than one year. Different incidence and severity of this viral disease among various age range and individuals with different background disease may indicate the pivotal role of host genetic factors in their prevalence and mortality rate. In this regards, present study was performed to review the most important genetic variants and factors in incidence and severity of SARS-CoV-2 based on the carried out studies in various populations.  
Materials and methods: Databases including PubMed, PubMed Central, Google Scholar, Bing, medRxiv and COVID-19 host genetics initiative were explored using key words including gene polymorphism, gene expression, gene variant, infection risk and disease severity to find the papers regarding genetic factors association with SARS-CoV-2 and its severity.
Results and Conclusion: Its seems that in addition to the HLA system variants and the genes related to interferons as well as IFITM3, ACE2, TMPRSS2, CD147, ACE and TLR7 genes are the most important genes which are involved in SARS-CoV-2 pathogenesis. Investigating the association of the most important genetic variants among different populations with SARS-Cov-2 can provide the way towards more targeted therapies for this disease. Moreover, by recognizing those variants, more efficient steps can be taken in early identification of the high risk carriers of the same next generation viruses.