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On Saturday, July 3, 2021, the Sonoma County Health Department was alerted to three cases of COVID-19 among residents of a homeless shelter in Santa Rosa, California. Among 153 shelter residents, 83 (54%) were fully vaccinated; 71 (86%) vaccinated residents had received the Janssen COVID-19 vaccine and 12 (14%) received an mRNA (Pfizer BioNTech or Moderna) COVID-19 vaccine. Within 1 month, 116 shelter residents (76%) received positive SARS-CoV-2 test results, including 66 (80%) of 83 fully vaccinated residents and 50 (71%) of 70 residents who were not fully vaccinated. Nine (14%) of 66 fully vaccinated cases, compared with 1 of 50 (2%) of unvaccinated cases, were hospitalized with COVID-19. All hospitalized cases had at least one underlying medical condition. Two deaths occurred, one in a vaccinated resident and one in a resident who was not fully vaccinated. Specimens from 52 residents underwent whole genome sequencing; all were identified as SARS-CoV-2 (the virus that causes COVID-19) AY.13, a sublineage of the B.1.617.2 (Delta) variant. These findings suggest that comprehensive measures including routine testing, individual quarantine, mask wearing, and physical distancing are needed in addition to vaccination in homeless shelters and other similar congregate settings, particularly those with residents who are at high risk for severe COVID-19.

Competing Interest Statement

The authors have declared no competing interest.

Funding Statement

This study did not receive any funding

Author Declarations

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.


The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

The California Department of Health human subjects committee deemed this activity to be non-research. This activity was reviewed by CDC and was conducted consistent with applicable federal law and CDC policy

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Paper in collection COVID-19 SARS-CoV-2 preprints from medRxiv and bioRxiv

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