COMPARISON OF FOURTH WAVE VARIANT OF SARS-COV-2 AND ANCESTRAL WAVES, AN EXPERIENCE FROM A TERTIARY CARE HOSPITAL, KARACHI

Objective: The study aims to identify the key differences between ancestral strains and the fourth wave variant of SARS-CoV-2 by comparing the epidemiological and clinical profile of patients admitted since the commencement of CoVID-19 disease. Material and Methods: The data of all those patients who were SARS-CoV-2 positive from March 2020 to February 2022 was collected. Records of 99 patients admitted during the fourth were compared to admitted patients during three previous waves over a period of the past 23 months. Results: From Jan till 2nd February 2022, 30.6% PCR turned out to be positive which was remarkably raised from our previous records where the positivity record was 9.11%. After October 2021 there was a remarkable reduction in SARS- CoV-2 infection, afterwards, we appreciated a sudden surge in positive cases during the first week of January 2022 (137/557 (24%)). This trend then led to a rise and fall pattern to 290/720(40%), 180/530 (33%) and 68/398 (17%) during the second, third and fourth week of January respectively. The majority of symptomatic patients developed mild disease 335/454(78%) and only 99/454(22%) developed moderate to a severe disease requiring hospitalization which was lower than the previous waves 410/1457(28%). The total mortality rate during the last three waves was 9% which was much higher than the recent strain during which mortality was only 1%. Conclusion: Major epidemiological and clinical differences were observed between ancestral strains and fourth-wave variants of SARS-CoV-2 with decreased severity, fewer deaths, and a shorter hospital stay. Keywords: SARS -CoV-2, Omicron variants, Outbreak, Vaccination.