Transmission and Infectious SARS-CoV-2 Shedding Kinetics in Vaccinated and Unvaccinated Individuals

Abstract

Key Points Question Do individuals fully vaccinated against COVID-19 have a shorter duration of viable SARS-CoV-2 viral shedding and a lower rate of secondary transmission than in partially vaccinated or unvaccinated individuals? Findings In this cohort study of 173 health care workers, inpatients, and guardians and 45 participants in a community facility, secondary transmission of SARS-CoV-2 was significantly less common, and viable virus was detected for a shorter duration in fully vaccinated individuals than in partially vaccinated or unvaccinated individuals. Meaning Fully vaccinated individuals had a shorter duration of viable viral shedding and a lower rate of secondary transmission than partially vaccinated or unvaccinated individuals.

Comparison of outward transmission potential between vaccinated and partially vaccinated or unvaccinated individuals with the SARS-CoV-2 delta variant infection

“…All patients were investigated for the number of close contacts during their infectious period (from ≤2 days before symptom onset in symptomatic patients or ≤2 days before the diagnosis day in cases of asymptomatic patients to isolation)(3), and the number of contact individuals who were diagnosed with SARS-CoV-2 infection within 1 week of contact. Definition of close contacts were found in our previous study ( 3 ).…”

“…However, given the low number of fully vaccinated individuals in this study (n=6), we could not detect a significant difference in the duration of viable viral shedding between the two groups that was a different viral shedding kinetic cohort from the cohort for the calculation of the secondary attack rate ( 3 ). Nevertheless, this prospective cohort study builds on our earlier publication ( 3 ) with a different independent cohort involving more fully vaccinated or partially vaccinated and unvaccinated hospitalized patients with COVID-19 at varying degrees of severity. We evaluated the secondary attack rate and viral shedding kinetics in the same cohort and found that fully vaccinated individuals with SARS-CoV-2 infection had lower transmissibility than partially vaccinated or unvaccinated individuals.…”

“…Our previous study reported that fully vaccinated individuals had a lower secondary attack rate than partially vaccinated or unvaccinated individuals ( 3 ). However, given the low number of fully vaccinated individuals in this study (n=6), we could not detect a significant difference in the duration of viable viral shedding between the two groups that was a different viral shedding kinetic cohort from the cohort for the calculation of the secondary attack rate ( 3 ).…”

“…Our previous study reported that fully vaccinated individuals had a lower secondary attack rate than partially vaccinated or unvaccinated individuals ( 3 ). However, given the low number of fully vaccinated individuals in this study (n=6), we could not detect a significant difference in the duration of viable viral shedding between the two groups that was a different viral shedding kinetic cohort from the cohort for the calculation of the secondary attack rate ( 3 ). Nevertheless, this prospective cohort study builds on our earlier publication ( 3 ) with a different independent cohort involving more fully vaccinated or partially vaccinated and unvaccinated hospitalized patients with COVID-19 at varying degrees of severity.…”

“…Genomic and subgenomic PCR was performed the same method as described in our previous studies ( 3 ). A cut-off value of negative conversion in genomic and subgenomic PCR was a cycle threshold (Ct) of 36, equivalent to a viral copy number of 2.6 log copies/mL, a 95% limit of detection.…”