Viral Load Among Vaccinated and Unvaccinated, Asymptomatic and Symptomatic Persons Infected With the SARS-CoV-2 Delta Variant

Abstract

We found no significant difference in cycle threshold values between vaccinated and unvaccinated persons infected with severe acute respiratory syndrome coronavirus 2 Delta, overall or stratified by symptoms. Given the substantial proportion of asymptomatic vaccine breakthrough cases with high viral levels, interventions, including masking and testing, should be considered in settings with elevated coronavirus disease 2019 transmission.

Keywords: 19; COVID; Ct value; Delta variant; SARS-CoV-2; asymptomatic testing.

Figure 1.

SARS-CoV-2 cycle threshold values in asymptomatic, symptomatic, vaccinated, and unvaccinated individuals in California. SARS-CoV-2 reverse transcription polymerase chain reaction cycle threshold values for specimens from patients by vaccine status from Healthy Yolo Together (City of Davis and Yolo County, CA, USA) (A) and from specimens by vaccine and symptom status from Unidos en Salud (Mission District, San Francisco, CA, USA) (B). Box plots show first quartile, median, and third quartiles in the shaded region; diamonds indicate outliers beyond 1.5 times the interquartile range; P values were calculated with 2-sided t tests. Abbreviations: Ct, cycle threshold; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2.