COVID -19 is an infectious disease caused by the novel coronavirus. The first known outbreak was reported in China in December 2019 and quickly spread globally. Therefore, WHO declared a public health emergency of international concern on 30 January 2020 and a pandemic on 11 March 2020 (Agrawal et al., 2020).SARS-CoV-2 (Severe acute respiratory syndrome coronavirus 2) is an RNA virus that causes the respiratory illness responsible for the COVID-19 disease (Coronaviridae Study Group of the International Committee on Taxonomy of Viruses, 2020; Zimmer, 2021). Globally SARS-CoV-2 has infected 480,957,051 people of which 6,123,616 have died during the pandemic and in India 43,020,723 people were infected and 521,035 died due to COVID-19 (As of March 28th, 2022; source: COVID-19 Dashboard by the Center for Systems Science and Engineering (CSSE) at Johns Hopkins University (JHU) (COVID-19, 2024). Vaccination remains the most potent way to manage the pandemic caused by viruses and other microbes. Vaccines are complex biological preparations that differ from pharmaceutical products as they are derived from living organisms. Currently, more than 153 vaccine candidates are in the clinical trial phases and 196 vaccine candidates are in pre-clinical development phases against COVID-19. These vaccines cover almost all types of vaccine technologies such as protein subunit, viral vector (non-replicating), DNA, Inactivated virus, RNA, viral vector (replicating), Viral Vector replicating +Antigen presenting cell (VVr), live attenuated virus, and Viral Vector non replicating +Antigen presenting cell (VVnr) (COVID-19, 2022).

In India, currently, four vaccines against COVID-19 viz.: Covishield, Covaxin, Sputnik V and ZyCoV-D got emergency use approval from regulatory authorities in India. The Covishield is a viral vector (non-replicating) vaccine developed by the University of Oxford in partnership with British-Swedish firm AstraZeneca and manufactured by the Serum Institute of India (Voysey et al., 2021). Covaxin is an inactivated vaccine developed by Bharat Biotech in collaboration with the Indian Council of Medical Research, India (Ella et al., 2021). Sputnik V is a viral vector (non-replicating) vaccine developed by Gamaleya National Research Institute of Epidemiology and Microbiology in partnership with the Russian Direct Investment Fund (RDIF), Russia, and manufactured by Dr. Reddy's Laboratories (Logunov et al., 2020). ZyCoV-D is a DNA vaccine candidate developed by Cadila Healthcare Ltd., Ahmedabad in collaboration with the Department of Biotechnology, India (Momin et al., 2021). Furthermore, five vaccine candidates were being developed by Indian manufacturers which are Novavax (NVX-CoV2373 Protein Subunit) by Serum Institute of India, Recombinant Protein Antigen based vaccine (Corbevax) by Biological E. Ltd., HGCO 19 (mRNA based vaccine) by Gennova Biopharmaceutical, Inactivated rabies vector vaccine by Bharat Biotech International Ltd. and Vesiculo Vax Platform based vaccine by Aurobindo pharma. Efficacy and safety evaluation of COVID-19 vaccines with limited available resources within given short span of time is a strenuous task as different manufacturers were using different technological platforms to manufacture the vaccines. Even with reasonably established techniques such as mRNA vaccines, inactivated vaccines, and recombinant viral vector-based vaccines, it is difficult to define and unify the requirements for the vaccines (Felsenstein et al., 2020; Yuki et al., 2020).

In the present study, the ChAdOx1 nCoV-19 Corona Virus Vaccine has been used for quality control evaluation purposes. ChAdOx1 nCoV-19 Corona Virus Vaccine was manufactured by using a replication-deficient chimpanzee adenovirus vector encoding the SARS-CoV-2 Spike (S) glycoprotein. Each dose of 0.5 ml contains 5 × 1010 viral particles produced in human embryonic kidney-HEK293 cells. The vaccine is being evaluated with the following quality control methods for detection of Spike protein of recombinant COVID-19 vaccine namely. Infectivity assay, DNA isolation and quantitative RT-PCR, DNA isolation and PCR, RNA isolation and quantitative RT-PCR, Immunofluorescence and Immunoblotting.