Comparison of secondary attack rate and viable virus shedding between patients with SARS‐CoV‐2 Delta and Omicron variants: A prospective cohort study

Abstract

There are limited data comparing the transmission rates and kinetics of viable virus shedding of the Omicron variant to those of the Delta variant. We compared these rates in hospitalized patients infected with Delta and Omicron variants. We prospectively enrolled adult patients with COVID‐19 admitted to a tertiary care hospital in South Korea between September 2021 and May 2022. Secondary attack rates were calculated by epidemiologic investigation, and daily saliva samples were collected to evaluate viral shedding kinetics. Genomic and subgenomic SARS‐CoV‐2 RNA was measured by PCR, and virus culture was performed from daily saliva samples. A total of 88 patients with COVID‐19 who agreed to daily sampling and were interviewed, were included. Of the 88 patients, 48 (59%) were infected with Delta, and 34 (41%) with Omicron; a further 5 patients gave undetectable or inconclusive RNA PCR results and 1 was suspected of being coinfected with both variants. Omicron group had a higher secondary attack rate (31% [38/124] vs. 7% [34/456], p < 0.001). Survival analysis revealed that shorter viable virus shedding period was observed in Omicron variant compared with Delta variant (median 4, IQR [1−7], vs. 8.5 days, IQR [5–12 days], p < 0.001). Multivariable analysis revealed that moderate‐to‐critical disease severity (HR: 1.96), and immunocompromised status (HR: 2.17) were independent predictors of prolonged viral shedding, whereas completion of initial vaccine series or first booster‐vaccinated status (HR: 0.49), and Omicron infection (HR: 0.44) were independently associated with shorter viable virus shedding. Patients with Omicron infections had higher transmission rates but shorter periods of transmissible virus shedding than those with Delta infections.

Clinical and virological features of asymptomatic and mild symptomatic patients with SARS‐CoV‐2 Omicron infection at Shanghai Fangcang shelter hospital

“…In contrast, early viral variants required a longer time to be cleared from the upper respiratory tract. [26][27][28] In this study, the median duration of negative conversion duration was 7 days for both asymptomatic and mild symptomatic patients, which might indicate that asymptomatic and mild symptomatic patients carry the virus and are infectious for a similar duration of time. It was also worth noting that the symptomatic patients had significantly lower C t values than the asymptomatic patients in the study.…”

“…Our results found that 225 (40.8%) patients achieved a virus‐free status within 7 days (data not shown). In contrast, early viral variants required a longer time to be cleared from the upper respiratory tract 26–28 . In this study, the median duration of negative conversion duration was 7 days for both asymptomatic and mild symptomatic patients, which might indicate that asymptomatic and mild symptomatic patients carry the virus and are infectious for a similar duration of time.…”

Judicious ending of isolation based on reverse transcription–polymerase chain reaction (RT-PCR) cycle threshold only for patients with coronavirus disease 2019 (COVID-19) requiring in-hospital therapy for longer than 20 days after symptom onset

“…First, the study period in the Ct group coincided with a predominance of the Omicron SARS-CoV-2 variant. Omicron exhibited a shorter duration of PCR positivity and viable virus shedding than Delta [ 22 ]. In addition, a higher proportion of patients were immunized against SARS-CoV-2 infection in the Ct group.…”

The epidemiological and clinical characteristics of COVID‐19 patients admitted to a Fangcang shelter hospital in Beijing before the change in China's prevention and control policy

“…Although COVID‐19 vaccines were developed rapidly and the vaccination was actively advocated for, constant viral mutations affected the efficacy of approved vaccines 2 . The infectivity and immune escape ability of SARS‐CoV‐2 variants constantly changed, which caused different disease characteristics in the epidemic dominated by the original strain to the Omicron variant, and the Omicron variant had higher infectivity and immune escape ability 3 . In view of the high infectivity and pathogenicity of SARS‐CoV‐2, China still adhered strictly to epidemic prevention and control and took the safety and health of people as the priority before the launch of the “New Ten Rules” policy.…”

“…2 The infectivity and immune escape ability of SARS-CoV-2 variants constantly changed, which caused different disease characteristics in the epidemic dominated by the original strain to the Omicron variant, and the Omicron variant had higher infectivity and immune escape ability. 3 In view of the high infectivity and pathogenicity of SARS-CoV-2, China still adhered strictly to epidemic prevention and control and took the safety and health of people as the priority before the launch of the "New Ten Rules" policy. The epidemic wave, in which the Omicron subvariant was dominant, in Shanghai and Guangzhou was successfully controlled and prevented through the "dynamic zeroing" strategy.…”