Comparative transmissibility of SARS-CoV-2 variants Delta and Alpha in New England, USA
Authors: Rebecca Earnest, Rockib Uddin, Nicholas Matluk, Nicholas Renzette, Sarah E. Turbett, Katherine J. Siddle, Christine Loreth, Gordon Adams, Christopher H. Tomkins-Tinch, Mary E. Petrone, Jessica E. Rothman, Mallery I. Breban, Robert Tobias Koch, Kendall Billig, Joseph R. Fauver, Chantal B.F. Vogels, Kaya Bilguvar, Bony De Kumar, Marie L. Landry, David R. Peaper, Kevin Kelly, Greg Omerza, Heather Grieser, Sim Meak, John Martha, Hannah B. Dewey, Susan Kales, Daniel Berenzy, Kristin Carpenter-Azevedo, Ewa King, Richard C. Huard, Vlad Novitsky, Mark Howison, Josephine Darpolor, Akarsh Manne, Rami Kantor, Sandra C. Smole, Catherine M. Brown, Timelia Fink, Andrew S. Lang, Glen R. Gallagher, Virginia E. Pitzer, Pardis C. Sabeti, Stacey Gabriel, Bronwyn L. MacInnis, Ryan Tewhey, Mark D. Adams, Daniel J. Park, Jacob E. Lemieux, Nathan D. Grubaugh, Ahmad Altajar, Alexandra DeJesus, Anderson Brito, Anne E. Watkins, Anthony Muyombwe, Brendan S. Blumenstiel, Caleb Neal, Chaney C. Kalinich, Chen Liu, Christine Loreth, Christopher Castaldi, Claire Pearson, Clare Bernard, Corey M. Nolet, David Ferguson, Erika Buzby, Eva Laszlo, Faye L. Reagan, Gina Vicente, Heather M. Rooke, Heidi Munger, Hillary Johnson, Irina R. Tikhonova, Isabel M. Ott, Jafar Razeq, James C. Meldrim, Jessica Brown, Jianhui Wang, Johanna Vostok, John P. Beauchamp, Jonna L. Grimsby, Joshua Hall, Katelyn S. Messer, Katie L. Larkin, Kyle Vernest, Lawrence C. Madoff, Lisa M. Green, Lori Webber, Luc Gagne, Maesha A. Ulcena, Marianne C. Ray, Marissa E. Fisher, Mary Barter, Matthew D. Lee, Matthew T. DeFelice, Michelle C. Cipicchio, Natasha L. Smith, Niall J. Lennon, Nicholas A. Fitzgerald, Nicholas Kerantzas, Pei Hui, Rachel Harrington, Randy Downing, Rashida Haye, Ryan Lynch, Scott E. Anderson, Scott Hennigan, Sean English, Seana Cofsky, Selina Clancy, Shrikant Mane, Stephanie Ash, Stephanie Baez, Steve Fleming, Steven Murphy, Sushma Chaluvadi, Tara Alpert, Trevor Rivard, Wade Schulz, Zoe M. Mandese
Journal: Cell Reports Medicine (2022)

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.