Outbreak of COVID-19 among vaccinated and unvaccinated homeless shelter residents — Sonoma County, California, July 2021

In July 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 fully vaccinated residents and 50 not fully vaccinated. 9 fully vaccinated and 1 unvaccinated were hospitalized for COVID-19. All hospitalized cases had at least one underlying medical condition. Two deaths occurred, one in a vaccinated resident and one in a non-vaccinated resident. Specimens from 52 residents underwent whole genome sequencing; all were identified as SARS-CoV-2, Delta Variant AY.13 lineage. Additional mitigation measures are needed in medically vulnerable congregate setting where limited resources make individual quarantine and isolation not feasible.