Viral dynamics of Omicron and Delta SARS-CoV-2 variants with implications for timing of release from isolation: a longitudinal cohort study

Abstract

BackgroundIn January 2022, United States guidelines shifted to recommend isolation for 5 days from symptom onset, followed by 5 days of mask wearing. However, viral dynamics and variant and vaccination impact on culture conversion are largely unknown.MethodsWe conducted a longitudinal study on a university campus, collecting daily anterior nasal swabs for at least 10 days for RT-PCR and culture, with antigen rapid diagnostic testing (RDT) on a subset. We compared culture positivity beyond day 5, time to culture conversion, and cycle threshold trend when calculated from diagnostic test, from symptom onset, by SARS-CoV-2 variant, and by vaccination status. We evaluated sensitivity and specificity of RDT on days 4-6 compared to culture.ResultsAmong 92 SARS-CoV-2 RT-PCR positive participants, all completed the initial vaccine series, 17 (18.5%) were infected with Delta and 75 (81.5%) with Omicron. Seventeen percent of participants had positive cultures beyond day 5 from symptom onset with the latest on day 12. There was no difference in time to culture conversion by variant or vaccination status. For the 14 sub-study participants, sensitivity and specificity of RDT were 100% and 86% respectively.ConclusionsThe majority of our Delta- and Omicron-infected cohort culture-converted by day 6, with no further impact of booster vaccination on sterilization or cycle threshold decay. We found that rapid antigen testing may provide reassurance of lack of infectiousness, though masking for a full 10 days is necessary to prevent transmission from the 17% of individuals who remain culture positive after isolation.Main PointBeyond day 5, 17% of our Delta and Omicron-infected cohort were culture positive. We saw no significant impact of booster vaccination on within-host Omicron viral dynamics. Additionally, we found that rapid antigen testing may provide reassurance of lack of infectiousness.

The effects of vaccination on the disease severity and factors for viral clearance and hospitalization in Omicron-infected patients :A retrospective observational cohort study from recent regional outbreaks in China

“…The policy of a five-day home quarantine plus a mask for additional five days, which was once implemented in the United States, has turned out quite inadequate and ineffective in inhibiting the viral transmission. 30 Altogether, the findings from the current study evidence that vaccination reduces disease severity and accelerates viral clearance, which signifies an urgency of vaccinating the elderly population with underlying illnesses to lower the risks of hospitalization. The median time of 15 NAN suggests that the infected should be quarantined for at least 15 days to minimize the transmission of the virus.…”

“…The policy of a five-day home quarantine plus a mask for additional five days, which was once implemented in the United States, has turned out quite inadequate and ineffective in inhibiting the viral transmission. 30…”

Buildout and integration of an automated high-throughput CLIA laboratory for SARS-CoV-2 testing on a large urban campus

“…A study on matched anterior nares swabs tested with both RT-PCR and Abbott BinaxNOW TM (Abbott Laboratories, Chicago, IL) was critical during the omicron surge as the demand for rapid diagnostic tests increased [28] . Data from the BU CTL, contact tracing, and sequencing data provided insight on vaccine efficacy [30] , transmission of SARS-CoV-2 in classrooms [31] , post-quarantine transmission and quarantine length [32] , and isolation release after infection [33] .…”

Prevalence and factors associated with antigen test positivity following SARS-CoV-2 infection among healthcare workers in Los Angeles

“…[12] While data demonstrate that boosted individuals were less likely to be infected with Omicron,[13] emerging data suggest those with breakthrough infections might have delayed viral decay and a longer time to viral clearance, which might explain our findings. [14, 15] However, we did not perform viral culture or repeat PCR testing as part of this study. Since this was an optional testing program, it is also possible that unvaccinated HCWs were more likely to have symptomatic infections that made them ineligible to participate in return-to-work testing, so findings should be interpreted within this context.…”