Infectivity, virulence and pathogenicity of different SARS-Cov-2 variants : a systematic review / Kristine L. Cortes, Franchesca Joy R. Delos Santos, Jane Erika T. Mabitasan, Karizz Mae C. Santos, Ella Marie Joy L. Vergara; Antonio Pascua.

Includes appendices and bibliographical references.

Abstract: Severe Acute Respiratory Syndrome Coronavirus 2 or SARS-CoV-2 is a new virus detected at the end of the year 2019; this virus causes pneumonia-like symptoms and was named Coronavirus disease or COVID-19. The virus has been speculated to originate from a bat genome, RaTG13 (Bat-Cov-RaTG13), with is 96% genomic sequencing. Further sequencing revealed 97.5% S protein similarity with Pangolin-CoV-2019. It was suspected that pangolin was a possible intermediate host of SARS-CoV-2. It was theorized that the recombination of both Bat-CoV-RaTG13 and Pangolin-Cov-2019 gave rise to SARS-CoV-2. The evident distinction between SARS-CoV and SARS-CoV-2 included mutations in the Receptor binding domian Spike protein of SARS-CoV-2 causing it to have 10-20x affinity with the ACE2 that is correlated with transmission and virulence of the virus. SARS-CoV-2 variants may be attributed to the characteristic of RNA virus' high rate of mutation. Hiscox (2021) stated that the mutations associated with these variants are highly related with greater transmission, which indicates that spike variants should be regularly monitored as part of genomic surveillance. With the aforementioned in mind, the researchers aim to provide a systematic review on each variants' infectivity, virulence and pathogenicity with the objective of advancing research knowledge on SARS-CoV-2 variants. Data collection from this study have utilized search engines such as Google scholar, ClinicalKey, EBSCO, UpToDate, Thieme ProQuest and uCentral; the use of key search terms helped the researchers attain a concise sythesis of results. Among all other variants, Delta has the highest percentage of transmissibility of 92.02% (GISAID, 2021). This was supported by WHO data stating 31 additional infected countries in a span of more than one month only, making it the most transmissible variant. Different mutations from each variant significantly alter their virulence and transmissibility. Delta variant, which proved to be most threatening among all other variants has P681R. Spike protein mutation that rendered the variant to have increased viral load that can consequently lead to decreased incubation period. The COVID-19 disease caused by SARS-CoV-2 mainly attacks the respiratory system of an infected individual. The common manifestation observed in lungs is the Diffuse Alveolar Damage with edema and hyaline membrane. As of August 2021, there has been no specific study discussing the uniqueness of pathogenicity of each variant. The study concludes that most vaccines gave a protection of >80% against Alpha variant and >70% against Beta, Gamma and Delta variant on fully vaccinated individuals. Therefore, there is no significant differences in VE, and it also proved that vaccines were remarkably effective against SARS-CoV-2 variants. A reduction in neutralization level was also observed, and a call for further study on the topic was also recommended.

Thesis - School of Medical Technology