Comparative transmissibility of SARS-CoV-2 variants Delta and Alpha in New England, USA
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 T. Koch, Kendall Billig, Joseph R. Fauver, Chantal B. F. Vogels, Kaya Bilgüvar, 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, J. Kebbeh Darpolor, Akarsh Manne, Rami Kantor, Sandra Smole, Catherine Brown, Timelia Fink, Andrew S. Lang, Glen R. Gallagher, Virginia E. Pitzer, Pardis C. Sabeti, Stacey Gabriel, Bronwyn MacInnis, Ahmad Altajar, Alexandra DeJesus, Anderson F. Brito, Anne E. Watkins, Anthony Muyombwe, Brendan Blumenstiel, Caleb Neal, Chaney C. Kalinich, Chen Liu, Christine Loreth, Christopher Castaldi, Claire Pearson, C. Bernard, Corey M. Nolet, David Ferguson, Erika Buzby, Éva László, 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 Beauchamp, Jonna Grimsby, Joshua C. Hall, Katelyn S. Messer, Katie Larkin, Kyle Vernest, Lawrence C. Madoff, Lisa M. Green, Lori Webber, Luc Gagne, Maesha A. Ulcena, Marianne C. Ray, Marissa Fisher, Mary Barter, Matthew Lee, Matthew DeFelice, Michelle Cipicchio, Natasha L. Smith, Niall J. Lennon, Nicholas FitzGerald, Nicholas Kerantzas, Pei Hui, Rachel Harrington, Randy Downing, Rashida Haye, Ryan Lynch
Abstract
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.