Household Transmission of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Alpha Variant—United States, 2021
Authors: Donnelly Marisa A P , Chuey Meagan R , Soto Raymond , Schwartz Noah G , Chu Victoria T , Konkle Stacey L , Sleweon Sadia , Ruffin Jasmine , Haberling Dana L , Guagliardo Sarah Anne J , Stoddard Robyn A , Anderson Raydel D , Morgan Clint N , Rossetti Rebecca , McCormick David W , Magleby Reed , Sheldon Sarah W , Dietrich Elizabeth A , Uehara Anna , Retchless Adam C , Tong Suxiang , Folster Jennifer M , Drobeniuc Jan , Petway Marla E , Austin Brett , Stous Sarah , McDonald Eric , Jain Seema , Hudziec Meghan M , Stringer Ginger , Albanese Bernadette A , Totten Sarah E , Staples J Erin , Killerby Marie E , Hughes Laura , Matanock Almea , Beatty Mark , Tate Jacqueline E , Kirking Hannah L , Hsu Christopher H ,   COVID-19 Household Transmission Team, Namageyo-Funa Apophia , Robinson Byron F , Foster Monique A , Alexander Lorraine N , O’Hegarty Michelle , Somers Tarah S , Escudero Horacio Ruisenor , Gomez Yessica , Abara Winston E , Garza Elizabeth , Humrighouse Ben W , Monroe Benjamin P , Arons Melissa , Cherney Blake , Chakrabarti Ayan K , Whaley Melissa J , Vuong Jeni , Ruth Laird J , Lindell Kristine , Georgi Joaudimir Castro , Visser Susanna N , Silver Maggie , Marx Grace E , Chancey Rebecca J , Mead Paul , Waltenburg Michelle A , Lehman Jennifer , Drexler Anna , Pawloski Jamie , Stovall Janae , Boroughs Karen L , Brault Aaron C , Weis-Torres Sabrina , Punkova Lili , Jia Tao Lily , Browning Peter , Bolcen Shanna , Maniatis Panagiotis , Park So Hee , Moss Kimberly M , Zellner Briana , Ortiz Kristina , Tao Ying , Li Yan , Kelleher Anna , Justin NG Han Jia , Zhang Jing , Lynch Brian , Cook Peter W , Paden Clinton R , Queen Krista , Medrzycki Magdalena , Rogers Shannon , Wong Phili , Jain Shilpi , Tejada Alexandra , Metz John Michael , David Ebenezer , Tang Xiaoling , Wynn Nhien T , Tiller Rebekah , Sakthivel Senthilkumar K , Velusamy Srinivasan , Whitaker Brett , Pray Ian W , Marcenac Perrine , Pratt Caroline Q , Ticho Zacks Rachael L , Yousaf Anna R , Segaloff Hannah E , Tobolowsky Farrell A , Firestone Melanie J , Schmitt-Matzen Emily N , Shragai Talya , LaVoie Stephen P , Mitchell Kaitlin F , Dionicio Bernabe Maria I , Zuniga-Groot Graciela , Manlutac Anna Liza M , Grano Christopher , Baily Heather , Burakoff Alexis , Webb Lindsey Martin , Stitzlein Tara M , Huynh-Templeman Kimberly , Dunyak Shaun , Pysnack Nicholas J , Delmonico Christopher , Giddmore Wyatt , Fortune Hannah M , Olsen Hunter , Alvarez Evelyn , Bundalian Cassandra N , Collins Hannah , Ricci Aleigha M , Ling Tia 
Published: February 2022

Abstract

Background
In Spring 2021, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) B.1.1.7 (Alpha) became the predominant variant in the United States. Research suggests that Alpha has increased transmissibility compared with non-Alpha lineages. We estimated household secondary infection risk (SIR), assessed characteristics associated with transmission, and compared symptoms of persons with Alpha and non-Alpha infections.

Methods
We followed households with SARS-CoV-2 infection for 2 weeks in San Diego County and metropolitan Denver, January to April 2021. We collected epidemiologic information and biospecimens for serology, reverse transcription–polymerase chain reaction (RT-PCR), and whole-genome sequencing. We stratified SIR and symptoms by lineage and identified characteristics associated with transmission using generalized estimating equations.

Results
We investigated 127 households with 322 household contacts; 72 households (56.7%) had member(s) with secondary infections. SIRs were not significantly higher for Alpha (61.0% [95% confidence interval, 52.4–69.0%]) than non-Alpha (55.6% [44.7–65.9%], P = .49). In households with Alpha, persons who identified as Asian or Hispanic/Latino had significantly higher SIRs than those who identified as White (P = .01 and .03, respectively). Close contact (eg, kissing, hugging) with primary cases was associated with increased transmission for all lineages. Persons with Alpha infection were more likely to report constitutional symptoms than persons with non-Alpha (86.9% vs 76.8%, P = .05).

Conclusions
Household SIRs were similar for Alpha and non-Alpha. Comparable SIRs may be due to saturation of transmission risk in households due to extensive close contact, or true lack of difference in transmission rates. Avoiding close contact within households may reduce SARS-CoV-2 transmission for all lineages among household members.