2. Seriousness of COVID-19
The development of vaccine against SARS-CoV-2 to contain its spread and help eliminate it from human population is a challenging task because there is lack of information on its biological properties, epidemiology, specific immune responses against it (Ahmed et al., 2020). There were 2494 laboratory-confirmed cases of MERS in 27 countries with 858 deaths (fatality rate 34.4%) and 8098 cases of SARS in 29 countries with 774 deaths (fatality rate ∼10%) globally (Zaki et al., 2012). However, COVID-19 brought whole world to stand still because its transmissibility is much ferocious compared to MERS- and SARS-CoVs which has infected more than 5.12 million people including more than 3.30 lakh deaths globally with ∼6.5% fatality rate by 20th May 2020 (Worldometer, 2020). Another problematic aspect of SARS-CoV infections is the presence of non-structural protein ‘papain-like protease’ which behaves like a deubiquitinase and may deubiquinate certain host cell proteins such as interferon factor-3 and nuclear factor kappa B, resulting in immune suppression (Baez-Santos et al., 2015). The potential of transmissibility or spread of viruses is measured in terms of reproductive number (R0). The stochastic and statistical methods have revealed an average R0 of 3.28 for SARS-CoV-2 which exceeds the WHO estimates of 1.4 to 2.5 (Morse et al., 2020). However, the transmissibility of SARS CoV and MERS CoV under hospital setting is comparatively lesser which is indicated by their lower (less than 1) R0 values (Chowell et al., 2015). It means a COVID-19 infected person can transmit the virus to 3.28 other persons, whereas SARS and MERS infected persons can transmit the virus to less than one other person. About 50% of the COVID-19 cases do not show signs of fever before hospitalization (Guan et al., 2020). Higher R0 value of SARS-CoV-2 along with the transmission from asymptomatic infected individuals (Rothe et al., 2020) indicates that control and prevention of COVID-19 will be challenging without development of a vaccine (Bai et al., 2020; Hu et al., 2020).
The ability of SARS-CoV-2 to mutate is fairly inconclusive. Point mutations were found to be insufficient to create a new virus. According to two recent independent studies in Italy at the “Lazzaro Spallanzani” National Institute for Infectious Diseases (IRCCS) in Rome and the Forensic Division of the Department of Biomedical Sciences and Public Health (DSBSP) at Ancona University Hospital, the genetic sequencing of the virus samples taken from Italian and Chinese patients revealed very small and insignificant variations (Etherington 2020). This is an indication that the SARS-CoV-2 remains fairly stable during the course of transmission across multiple individuals and populations. Thus, a vaccine, whenever it arrives, will potentially be effective broadly and for a considerable time of few years at a time (Etherington 2020). Although, no recombination events were detected in SARS-CoV-2 yet (Yu et al., 2020) two coronaviruses co-infecting the same host can make one acquire a genomic fragment of hundreds or thousands base-pair long by recombination which enables the virus to increase its ecological niche or make the leap to a new species (Gralinski et al., 2015). This recombination property of coronaviruses can be the reason for the emergence of SARS-CoV, MERS CoV, and now SARS-CoV-2 since 2002 (Chen, 2020). In a recent study 149 sites of mutations observed across the genome of 103 sequenced strains of SARS-CoV-2 resulted in two subtypes,viz . L and S subtype. Significant differences in geographical distribution, transmission ability, and severity of disease were observed between the two subtypes, which potentially creates further hindrances in vaccine design (Tang et al., 2020). Another study provides a direct evidence that mutations currently occurring in the SARS-CoV-2 genome have functional potential to impact the viral pathogenicity (Yao et al., 2020).