![]() A subset of samples (39%) were also sequenced using the Illumina MiSeq sequencing platform. ![]() Genotypes of all N1/N2-positive samples were determined using reverse transcription PCR (RT-PCR) single-nucleotide polymorphism analysis at 11 loci diagnostic for variants of concern (SARS-CoV-2 Variant ValuPanel assays | LGC Biosearch Technologies). Samples were routinely run multiple times for quality control replicates had very similar Ct values. Ct values were calculated with FastFinder software (UgenTec | FastFinder). Saliva samples from asymptomatic individuals were tested for the presence of the N1 and N2 regions of the viral nucleocapsid (N) gene using primers and probes described in the CDC 2019-Novel Coronavirus (2019-nCoV) Real-Time RT-PCR Diagnostic Panel using IntelliQube high-throughput quantitative polymerase chain reaction (PCR) instruments (LGC Biosearch Technologies). Only confirmed, fully vaccinated individuals were used in the analysis discordant samples, self-reported as vaccinated but unconfirmed, were treated as status unknown. Vaccination status was obtained at the time of contact tracing and confirmed in the California Vaccine Registry. HYTĭemographic information was collected from individuals at the time of registration. Individuals who had had only 1 dose or were tested within 2 weeks of the second dose, in the case of the Pfizer and Moderna vaccines, were not included in the analysis. Infections were classified as breakthrough infections if the individual was fully vaccinated (2 weeks following receipt of all vaccine doses). Anterior-nasal swab samples (iClean, Chenyang Global) were collected by certified lab technicians. Individuals 1 year of age and older, with or without symptoms, were eligible for testing. The outdoor, free BinaxNOW testing site was located at a public transport and commercial hub in the Mission District, a setting of ongoing transmission in San Francisco. ![]() The study population included individuals who sought SARS-CoV-2 testing at the UeS walk-up site, an ongoing academic (UC San Francisco, CZ Biohub, and UC Berkeley), community organization (Latino Task Force), and government (SFDPH) partnership. Smaller numbers of symptomatic individuals were processed using a different workflow and an antigen test therefore, they were not included in this study. ![]() Under supervision, samples were collected by individuals transferring their saliva into barcoded tubes (COVID-19 Testing | Campus Ready). Asymptomatic cases were classified as individuals not reporting symptoms for at least 24 hours before testing. Asymptomatic individuals over the age of 2 were eligible for testing. HYTĪs part of the response to coronavirus disease 2019 (COVID-19), UC Davis deployed an extensive free asymptomatic testing program that included the City of Davis and Yolo County (Healthy Yolo Together). METHODS Study Populationsĭata were collected on individuals who voluntarily sought testing for SARS-CoV-2 from 2 demographically distinct populations in California during a 2-month period (June 17–August 31, 2021), during which Delta was the predominant variant. Here, we report on cycle threshold (Ct) values among 869 fully vaccinated and unvaccinated individuals, asymptomatic and symptomatic at the time of testing, during a period of high transmission of the Delta variant in 2 distinct populations: Unidos en Salud (UeS) community-based testing in the Mission District of San Francisco and Healthy Yolo Together (HYT) asymptomatic testing through the University of California (UC), Davis. Reports predominantly from non-US settings suggest that viral loads from nasal swabs are similar among unvaccinated and vaccinated individuals other reports suggest that virus levels are lower in unvaccinated persons. ![]() Yet breakthrough cases occur, and this risk increases over time. Vaccines reduce infection, severe disease, and death from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Asymptomatic testing, COVID, 19, Ct value, SARS-CoV-2, Delta variant ![]()
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