Introduction Since its emergence in December of 2019, there have been over 10 variants of SARS-CoV-2 identified. Currently, omicron is the dominant variant in the United States. Though the variant is associated with a milder disease compared to the original strain of the virus, it exhibits a higher reproduction number, leading to increased transmissibility and infectivity. The current study investigates the differences between Omicron and the original SARS-CoV-2 pathologies.

Methods We conducted a search of the current literature to examine the differences in disease manifestation, complications following infection, and affected populations between the original strain and the Omicron variant. This was done by manually searching published articles up to June 2022 from the following databases: PubMed and Google Scholar. We searched for relevant clinical content using CDC and Lexi-Comp. We manually searched references of selected articles for additional information. Scientific articles were searched under English language restrictions. A total of 145 articles were retrieved, including clinical trials, journal articles, meta-analyses, randomized control trials, reviews, and systematic reviews if the data presented vital information for Omicron and COVID-19 infectivity and/or complications. Drug-induced damage and animal studies were excluded in this study because these subjects do not portray the damage caused by Omicron or COVID-19 in human subjects.

Results We found that the Omicron variant is associated with a shorter duration and decreased severity of symptoms, as well as a decreased likelihood of developing severe complications as acute respiratory distress syndrome, pneumonia, and pulmonary edema. Additionally, the original strain was more likely to be found in older, obese males, while the Omicron variant is more common in younger, overweight females. This increased infectivity without increased severity may be attributed to mutations in the receptor-binding domain of Omicron that confer an increased affinity to the angiotensin-converting enzyme 2 and transmembrane serine protease receptors. Additional mutations in the spike protein allow for immune system evasion and breakthrough infection despite vaccination. Yet, the variant exhibits decreased pathogenicity due to differences in cell fusion mechanisms, restricting the virus to mostly the upper respiratory tract.

Conclusion Our literature search found key differences in the disease presentation, affected population, and pathogenicity between the original SARS-CoV-2 strain and the currently dominating Omicron variant.