1. Introduction
The outbreak of rapidly spreading severe respiratory disease caused by
novel coronavirus (CoV) in December of 2019 in Wuhan, China has put
whole world on high alert. The World Health Organization (WHO) named it
COVID-19 and declared it a global pandemic on 30thJanuary 2020 (Kim et al., 2020). The disease has spread to more than 200
countries with over 5.12 million cases and more than 3.30 lakh deaths
worldwide by 21st May 2020 (Worldometer, 2020). These
numbers are still increasing rapidly. The normal life has been disrupted
as a result of mandatory lockdowns, isolations, and quarantines in
response to COVID-19 pandemic and has imposed a serious challenge to
global health system and economy (Gorbalenya et al., 2020; Kupferschmidt
et al., 2020). The coronaviruses represent an ongoing as well as future
threat to human health because of their wide distribution, higher
prevalence, higher recombination potential of their genomes, profound
genetic diversity, and increasing human-animal interaction (Hui et al.,
2020; Zhu et al., 2020). SARS-CoV-2 is relatively a large virus of
betacoronavirus genus containing a single-stranded positive-sense RNA
genome encapsulated within a membrane envelope (Morse et al., 2020). It
is one of the seven discrete coronavirus species capable of causing
disease in humans (Zhu et al., 2020). The Coronavirus Study Group (CSG)
of International Committee on Taxonomy of Viruses (ICTV) changed its
name from 2019-nCoV to SARS-CoV-2 because it was found to be a sister
virus of severe acute respiratory syndrome coronavirus (SARS-CoV) after
genomic analysis (Gorbalenya et al., 2020). The genomic analysis
revealed that SARS-CoV-19 genome is more closely related to bat RaTG13
SARS-CoV (96%) in particular and SARS-CoV (80%) in general compared to
middle east respiratory syndrome (MERS) CoV (54%) genome (Zhou et al.,
2020).
The genomic analysis reveals similarities in receptor-binding motif of
SARS-CoV-2 and SARS-CoV which directly binds human receptor protein
called angiotensin-converting enzyme-2 (ACE-2) to enter target cells.
This has direct bearing on its vaccine design, rapidity of vaccine
development, and prediction of its pandemic potential (Kim et al.,
2020). Similar to SARS-CoV and MERS-CoV, the predilection site of
SARS-CoV-2 is lower respiratory system and viral pneumonia occurs.
However, SARS-CoV-2 may also attack gastrointestinal tract, heart,
kidney, liver, and central nervous system resulting in death due to
multiple organ failure (Zhu et al., 2019). Though, the exact reservoir
of SARS-CoV-2 could not be established yet with surety, its
human-to-human transmission is now well established, and the verified
cases are growing at an alarming rate. After crossing the species
barrier, within a month human to human transmission became responsible
for widespread and rapid dissemination of virus across the entire
population of China with no pre-existing immunity (Chen, 2020; Wu et
al., 2020). The current ferocious spread of COVID-19 indicates that
SARS-CoV-2 is more transmissible or contagious than SARS-and MERS-CoVs.
This grim situation of COVID-19 demands the generation of targeted
vaccines and therapies for reducing the associated morbidity and
mortality. However, the risk of contracting COVID-19 is highest in
healthcare workers, elderly people over 60 years of age, and people
suffering from diabetes and hypertension (Huang et al., 2020). Thus,
these people need to be prioritized for vaccine trials and licensure
(Chen et al., 2020).