Comparative transmissibility of SARS-CoV-2 variants Delta and Alpha in New England, USA

New England Variant Investigation Team

Research output: Contribution to journalArticlepeer-review

74 Scopus citations


The SARS-CoV-2 Delta variant rose to dominance in mid-2021, likely propelled by an estimated 40%–80% increased transmissibility over Alpha. To investigate if this ostensible difference in transmissibility is uniform across populations, we partner with public health programs from all six states in New England in the United States. We compare logistic growth rates during each variant's respective emergence period, finding that Delta emerged 1.37–2.63 times faster than Alpha (range across states). We compute variant-specific effective reproductive numbers, estimating that Delta is 63%–167% more transmissible than Alpha (range across states). Finally, we estimate that Delta infections generate on average 6.2 (95% CI 3.1–10.9) times more viral RNA copies per milliliter than Alpha infections during their respective emergence. Overall, our evidence suggests that Delta's enhanced transmissibility can be attributed to its innate ability to increase infectiousness, but its epidemiological dynamics may vary depending on underlying population attributes and sequencing data availability.

Original languageEnglish (US)
Article number100583
JournalCell Reports Medicine
Issue number4
StatePublished - Apr 19 2022
Externally publishedYes


  • COVID-19
  • SARS-CoV-2
  • VOC
  • genomic epidemiology
  • transmissibility
  • variant of concern
  • viral emergence
  • viral sequencing

ASJC Scopus subject areas

  • General Biochemistry, Genetics and Molecular Biology


Dive into the research topics of 'Comparative transmissibility of SARS-CoV-2 variants Delta and Alpha in New England, USA'. Together they form a unique fingerprint.

Cite this