Thread by @MisterRan

Shedding of Infectious SARS-CoV-2 Despite Vaccination.

The SARS-CoV-2 Delta variant might cause high viral loads, is highly transmissible, and contains mutations that confer partial immune escape

medrxiv.org/content/10.110…

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Read this very carefully:

Outbreak investigations suggest that vaccinated persons can spread Delta.

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We observed low Ct values (<25) in 212 of 310 fully vaccinated (68%; Figure 1A) and 246 of 389 (63%) unvaccinated individuals. Testing a subset of low-Ct samples revealed infectious SARS-CoV-2 in 15 of 17 specimens (88%) from unvaccinated individuals

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and 37 of 39 (95%) from vaccinated people .

Low Ct values were detected in vaccinated people regardless of symptoms at the time of testing (Figure 1C). Ct values <25 were detected in 7 of 24 unvaccinated (29%; CI: 13-51%)

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and 9 of 11 fully vaccinated asymptomatic individuals (82%; CI: 48-97%), and 158 of 232 unvaccinated (68%, CI: 62-74%) and 156 of 225 fully vaccinated (69%; CI: 63-75%) symptomatic individuals.

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Combined with other studies these data indicate that vaccinated and unvaccinated individuals infected with the Delta variant might transmit infection
Importantly, we show that infectious SARS-CoV-2 is frequently found even in vaccinated persons when specimen Ct values are low

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The inclusion of viruses from Pango lineages B.1.617.2, AY.2, and AY.3
and multiple counties without a linking outbreak
indicate that Delta-lineage SARS-CoV-2 can achieve low Ct values consistent with transmissibility in fully vaccinated individuals across a range of settings

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Vaccinated and unvaccinated persons should get tested when symptomatic or after close contact with someone with suspected or confirmed COVID-19.

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Individuals infected with SARS-CoV-2 despite full vaccination have low Ct values and shed infectious virus.
A. Ct values for SARS-CoV-2-positive specimens grouped by vaccination status. RT-PCR was performed by Exact Sciences Corporation, responsible for over 10% of all PCR

tests in Wisconsin during this period, using a qualitative diagnostic assay targeting the SARS-CoV-2 N gene (oligonucleotides identical to CDC’s N1 primer and probe set) that has been authorized for emergency use by FDA (fda.gov/media/138328/d…).

B. Infectiousness was determined for a subset of N1 Ct-matched specimens with Ct <25 by inoculation onto Vero E6 TMPRSS2 cells and determining presence of cytopathic effects (CPE) after 5 days in culture. Specimens were selected by N1 Ct-matching between fully vaccinated and not

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fully vaccinated persons, then specimens from persons with unknown vaccination status were excluded from the analysis. Circles indicate presence of CPE; ‘X’ indicates no CPE detected. C. N1 Ct values for SARS-CoV-2-positive specimens grouped by vaccination status for

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individuals who were symptomatic or asymptomatic, or those whose symptom status was not determined, at the time of testing. In A and C, boxplots represent mean N1 Ct values +/- one standard deviation. P-values were calculated by comparing mean Ct values by

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independent two-group Mann-Whitney U tests.

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Concordance between self-reported vaccination status and the Wisconsin Immunization Registry (WIR) or Wisconsin Electronic Disease Surveillance System (WEDSS). For all individuals, vaccination status was determined using WIR/WEDSS electronic registries when data were

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available. Individuals were identified as unvaccinated at the time of testing if WIR/WEDSS data indicated receipt of a first SARS-CoV-2 vaccine dose after the test date.

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Density distributions of unvaccinated and vaccinated specimen collection dates by day since symptom onset. Day 0 on the x-axis denotes self-reported day of symptom onset. Negative values for days indicate specimen collection prior to symptom onset.

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Symptom onset data were available for n=263 unvaccinated cases and n=232 vaccinated cases.