Abstract
Background
Households have emerged as important venues for SARS-CoV-2 transmission. Little is known, however, regarding the magnitude and determinants of household transmission in increasingly vaccinated populations.
Methods
From September 2020 to January 2022, symptomatic non-hospitalized individuals with SARS-CoV-2 infection by RNA detection were identified within 5 days of symptom onset; all individuals resided with at least one other SARS-CoV-2-uninfected household member. These infected persons (cases) and their household members (contacts) were subsequently followed with questionnaire-based measurement and serial nasal specimen collection. The primary outcome was SARS-CoV-2 infection among contacts.
Results
We evaluated 42 cases and their 74 household contacts. Among the contacts, 32 (43%) became infected, of whom 5/32 (16%) were asymptomatic; 81% of transmissions occurred by 5 days after the case’s symptom onset. From 21 unvaccinated cases, 14-day cumulative incidence of SARS-CoV-2 infection among contacts was 18/40 (45%; 95% CI: 29, 62), most of whom were unvaccinated. From 21 vaccinated cases, 14-day cumulative incidence of SARS-CoV-2 infection was 14/34 (41%; 95% CI: 25, 59) among all contacts and 12/29 (41%; 95% CI: 24, 61) among vaccinated contacts. At least one co-morbid condition among cases and 10 or more days of RNA detection in cases were associated with increased risk of infection among contacts.
Conclusions
Among households including individuals with symptomatic SARS-CoV-2 infection, both vaccinated-to-vaccinated and unvaccinated-to-unvaccinated transmission of SARS-CoV-2 to household contacts was common. Because vaccination alone did not notably reduce risk of infection, household contacts will need to employ additional interventions to avoid infection.
Keywords: SARS-CoV-2, household transmission, epidemiology, infectious viral shedding
Contributor Information
J Daniel Kelly, Department of Epidemiology and Biostatistics, University of California, San Francisco, CA, USA; Institute for Global Health Sciences, University of California, San Francisco, CA, USA; F.I. Proctor Foundation, University of California, San Francisco, CA, USA; San Francisco VA Medical Center, San Francisco, CA, USA.
Scott Lu, Department of Epidemiology and Biostatistics, University of California, San Francisco, CA, USA; Institute for Global Health Sciences, University of California, San Francisco, CA, USA.
Khamal Anglin, Institute for Global Health Sciences, University of California, San Francisco, CA, USA.
Miguel Garcia-Knight, Department of Microbiology and Immunology, UCSF.
Jesus Pineda-Ramirez, Institute for Global Health Sciences, University of California, San Francisco, CA, USA.
Sarah A Goldberg, Department of Epidemiology and Biostatistics, University of California, San Francisco, CA, USA.
Michel Tassetto, Department of Microbiology and Immunology, UCSF.
Amethyst Zhang, Department of Microbiology and Immunology, UCSF.
Kevin Donohue, School of Medicine, University of California, San Francisco, CA, USA.
Michelle C Davidson, School of Medicine, University of California, San Francisco, CA, USA.
Mariela Romero, Institute for Global Health Sciences, University of California, San Francisco, CA, USA.
Ruth Diaz Sanchez, Institute for Global Health Sciences, University of California, San Francisco, CA, USA.
Manuella Djomaleu, School of Medicine, University of California, San Francisco, CA, USA.
Sujata Mathur, Department of Epidemiology and Biostatistics, University of California, San Francisco, CA, USA.
Jessica Y Chen, Institute for Global Health Sciences, University of California, San Francisco, CA, USA.
Carrie A Forman, School of Medicine, Drexel University, Philadelphia, PA, USA.
Venice Servellita, Department of Laboratory Medicine, University of California, San Francisco, CA, USA.
Rubi D Montejano, School of Medicine, University of California, San Francisco, CA, USA.
Joshua R Shak, San Francisco VA Medical Center, San Francisco, CA, USA.
George W Rutherford, Department of Epidemiology and Biostatistics, University of California, San Francisco, CA, USA; Institute for Global Health Sciences, University of California, San Francisco, CA, USA.
Steven G Deeks, Division of HIV, Infectious Diseases and Global Medicine, Zuckerberg San Francisco General Hospital, San Francisco, CA, USA.
Glen R Abedi, (CDC), Respiratory Viruses Branch, Division of Viral Diseases, CDC, Atlanta, GA, USA.
Melissa A Rolfes, (CDC), Respiratory Viruses Branch, Division of Viral Diseases, CDC, Atlanta, GA, USA.
Sharon Saydah, (CDC), Respiratory Viruses Branch, Division of Viral Diseases, CDC, Atlanta, GA, USA.
Melissa Briggs-Hagen, (CDC), Respiratory Viruses Branch, Division of Viral Diseases, CDC, Atlanta, GA, USA.
Michael J Peluso, Division of HIV, Infectious Diseases and Global Medicine, Zuckerberg San Francisco General Hospital, San Francisco, CA, USA.
Charles Chiu, Department of Laboratory Medicine, University of California, San Francisco, CA, USA.
Claire M Midgley, (CDC), Respiratory Viruses Branch, Division of Viral Diseases, CDC, Atlanta, GA, USA.
Raul Andino, Department of Microbiology and Immunology, UCSF.
Jeffrey N Martin, Department of Epidemiology and Biostatistics, University of California, San Francisco, CA, USA.
Supplementary Material
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