Evidence of early community transmission of Omicron (B1.1.529) in Delhi- A city with very high seropositivity and past-exposure!

Summary

Background

Since identification, infections by new SARS-CoV-2 variant Omicron are rapidly increasing worldwide. There is huge gap of knowledge regarding virus behaviour in the population from low and middle income countries. Delhi being unique population with a high seropositivity and vaccination rate against COVID-19 infection. We aimed to study the epidemiological and clinical presentations of few early cases of community spread of Omicron infection in the state.

Methods

This is a prospective study where respiratory specimen from all RT-PCR confirmed positive cases between November 25 ^th-December 23 ^rd 2021 collected from five districts of Delhi were subjected to whole genome sequencing. Complete demographic and clinical details were recorded. We also analyzed the formation of local and familial clusters and eventual community transmission.

Findings

Out of the 264 cases included during study period, 68.9% (n=182)were identified as Delta and its sub-lineages while 31.06% (n=82) were Omicron with BA.1 as the predominant sub-lineage (73.1%). Most of the Omicron cases were asymptomatic (n=50,61%) and not requiring any hospitalizations. A total of 72 (87.8%) cases were fully vaccinated. 39.1% (n=32) had a history of travel and/or contacts while 60.9 (n=50) showed a community transmission. A steep increase in the daily progression of Omicron cases with its preponderance in the community was observed from 1.8% to 54%.

Interpretation

This study is among the first from India to provide the evidence of community transmission of Omicron with significantly increased breakthrough infections, decreased hospitalization rates, and lower rate of symptomatic infections among individuals with high seropositivity against SARS-CoV-2 infections.