No Significant Difference in Viral Load Between Vaccinated and Unvaccinated, Asymptomatic and Symptomatic Groups When Infected with SARS-CoV-2 Delta Variant
(preprint, 2021)
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Shout-out to Dr Jonathan J Couey at Gigaohm Biological for bringing this paper to light.
Abstract
We found no significant difference in cycle threshold values between vaccinated and unvaccinated, asymptomatic and symptomatic groups infected with SARS-CoV-2 Delta. Given the substantial proportion of asymptomatic vaccine breakthrough cases with high viral levels, interventions, including masking and testing, should be considered for all in settings with elevated COVID-19 transmission.
Background
Vaccines reduce infection, severe disease, and death from SARS-CoV-2 (COVID-19) [1], yet breakthrough cases occur [2]. Several reports show no difference in cycle threshold values (Ct-values) between vaccinated and unvaccinated individuals [2, 3, 4]; however, others have suggested that breakthrough infections, particularly among asymptomatic individuals, have a lower viral load and therefore may be less likely to result in transmission [5, 6].
Effective epidemic control requires contemporary data to guide public health mitigation measures. Here, we report on Ct-values among fully vaccinated and unvaccinated individuals, asymptomatic and symptomatic at time of testing, during a period of high transmission of the Delta variant in two distinct populations: a Unidos en Salud (UeS) community-based site in the Mission District of San Francisco and Healthy Yolo Together (HYT) asymptomatic testing through the University of California (UC), Davis.
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, California) (Panel A) and from specimens by vaccine and symptom status from Unidos en Salud (Mission District, San Francisco, California) (Panel B). Box plots show first quartile, median, and third quartiles in shaded region; diamonds indicate outliers beyond 1.5 times the interquartile range; p-values were calculated with two-sided t-tests.
Full paper:
https://www.medrxiv.org/content/10.1101/2021.09.28.21264262v2