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Introduction
Immunization is the foundation of public health for any nation. The first vaccination was done by Edward Jenner against small pox in a 8 year old boy using cowpox lesion scratching from a milk maid1-3. Different types of vaccines are available against different disease-causing pathogens. Vaccines are usually classified into live attenuated and killed inactivated vaccines. Live attenuated vaccines have weakened but viable pathogen as antigens, while in killed vaccines; pathogens are inactivated by heat or chemicals. Over years, vaccines have been developed using specific biomolecules like proteins, DNA and mRNA4-6. Subunit vaccine makes use of the highly antigenic portion of viral and bacterial proteins, while conjugate vaccines are bacterial lipopolysaccharides covalently bound to an antigenic carrier protein to provide broad spectrum immunity. The protein-based vaccines can be produced using recombinant DNA technology. DNA and mRNA based vaccines have recently become strong candidates5,6.
Recent pandemic of Coronavirus Disease 2019 (COVID-19) witnessed fast track research for developing a vaccine against its causative agent, severe acute respiratory syndrome coronavirus-2 (SARS CoV-2). Since 2019, more than 760 million people were infected and the virus killed 6.9 million deaths globally (https://www.who.int). SARS-CoV2 is a positive single-stranded ribonucleic acid (RNA) virus with a genome size of 26-36 kilobases and belongs to the Coroniviridaefamily. Several studies have shown that SARS-CoV2 has genetic similarities to the earlier known coronaviruses, severe acute respiratory syndrome coronavirus(SARS-CoV)and Middle East respiratory syndrome coronavirus (MERS-CoV), which also infect humans7-9.The genome of SARS-CoV2 encodes four main structural proteins, i.e., spike glycoprotein (S), membrane protein (M), envelope (E) and nucleocapsid (N) proteins. These structural proteins are essential to maintain function and structure of the virus. The viral genome also carries genes for non-structural proteins (NSP) and other accessory proteins8,9. Sixteen NSPs are expressed from the 5’-end of the RNA genome and each NSP has been shown to have a significant function in establishing infection and immune evasion10. NSP7, NSP8 and NSP12 (also known as RNA-dependent RNA polymerase [RdRP]) form the replication-transcription complex (RTC) that is important for viral replication and transcription11. NSP9 is a RNA-binding protein shown to have a role in the formation of the RTC12,13. Zong et al....