Studying Community Transmission of SARS-CoV-2 During the Delta wave in New York City

Nov 9, 2023 | News

In a new study co-authored by PRI Epidemiology and Modeling Co-Lead (Columbia MSPH/CPID), Jeffrey Shaman, researchers explore community transmission of SARS-CoV-2 during the Delta wave in New York City. The Delta variant (B.1.617.2) emerged in late 2020 and became the dominant VOC globally in the summer of 2021. While the epidemiological features of the Delta variant have been extensively studied, how those characteristics shaped community transmission in urban settings remains poorly understood.

Using high-resolution contact tracing data and testing records, the authors analyzed the transmission of SARS-CoV-2 during the Delta wave within New York City (NYC) from May 2021 to October 2021. They reconstructed transmission networks at the individual level and across 177 ZIP code areas, examined network structure and spatial spread patterns, and used statistical analysis to estimate the effects of factors associated with COVID-19 spread.’Using high-resolution contact tracing data and testing records, The authors analyzed the transmission of SARS-CoV-2 during the Delta wave within New York City (NYC) from May 2021 to October 2021. They reconstructed transmission networks at the individual level and across 177 ZIP code areas, examined network structure and spatial spread patterns, and used statistical analysis to estimate the effects of factors associated with COVID-19 spread.

Key Findings

  • Researchers found considerable individual variations in reported contacts and secondary infections, consistent with the pre-Delta period. Compared with earlier waves, Delta-period has more frequent long-range transmission events across ZIP codes.
  • Using socioeconomic, mobility and COVID-19 surveillance data at the ZIP code level, researchers found that a larger number of cumulative cases in a ZIP code area is associated with reduced within- and cross-ZIP code transmission and the number of visitors to each ZIP code is positively associated with the number of non-household infections identified through contact tracing and testing.

Conclusion

The Delta variant produced greater long-range spatial transmission across NYC ZIP code areas, likely caused by its increased transmissibility and elevated human mobility during the study period. Findings highlight the potential role of population immunity in reducing transmission of VOCs. Quantifying variability of immunity is critical for identifying subpopulations susceptible to future VOCs. In addition, non-pharmaceutical interventions limiting human mobility likely reduced SARS-CoV-2 spread over successive pandemic waves and should be encouraged for reducing transmission of future VOCs.

Read the full report at BMC Infectious Diseases.