High Rate of Asymptomatic Carriage Associated with Variant Strain Omicron

Abstract

The early widespread dissemination of Omicron indicates the urgent need to better understand the transmission dynamics of this variant, including asymptomatic spread among immunocompetent and immunosuppressed populations. In early December 2021, the Ubuntu clinical trial, designed to evaluate efficacy of the mRNA-1273 vaccine (Moderna) among persons living with HIV (PLWH), began enrolling participants. Nasal swabs are routinely obtained at the initial vaccination visit, which requires participants to be clinically well to receive their initial jab. Of the initial 230 participants enrolled between December 2 and December 17, 2021, 71 (31%) were PCR positive for SARS-CoV-2: all of whom were subsequently confirmed by S gene dropout to be Omicron; 48% of the tested samples had cycle threshold (CT) values <25 and 18% less than 20, indicative of high titers of asymptomatic shedding. Asymptomatic carriage rates were similar in SARS-CoV-2 seropositive and seronegative persons (27% respectively). These data are in stark contrast to COVID-19 vaccine studies conducted pre-Omicron, where the SARS-CoV-2 PCR positivity rate at the first vaccination visit ranged from <1%-2.4%, including a cohort of over 1,200 PLWH largely enrolled in South Africa during the Beta outbreak. We also evaluated asymptomatic carriage in a sub study of the Sisonke vaccine trial conducted in South African health care workers, which indicated 2.6% asymptomatic carriage during the Beta and Delta outbreaks and subsequently rose to 16% in both PLWH and PHLWH during the Omicron period. These findings strongly suggest that Omicron has a much higher rate of asymptomatic carriage than other VOC and this high prevalence of asymptomatic infection is likely a major factor in the widespread, rapid dissemination of the variant globally, even among populations with high prior rates of SARS-COV-2 infection.

Detection of SARS-CoV-2 Omicron variant (B.1.1.529) infection of white-tailed deer

“…All retested samples showed amplification of orf1a/b and S gene dropout in the TaqPath multiplex assay, suggestive of Omicron VoC as previously described 21 . However, we also observed an unusual N-gene dropout or Ct value shift in most of the samples with the TaqPath assay.…”

Reduced risk of hospitalisation among reported COVID-19 cases infected with the SARS-CoV-2 Omicron BA.1 variant compared with the Delta variant, Norway, December 2021 to January 2022

“…Conversely, another potential bias could be systematic differences between the variants among non-diagnosed cases. For example, Omicron infections may have a higher rate of asymptomatic carriage than other variants of concern [ 13 ]. Such infections may be less likely to be diagnosed, which could result in an underestimation of the true reduction in risk of hospitalisation for Omicron compared with Delta.…”

Emergence of SARS-CoV-2 Omicron (B.1.1.529) variant, salient features, high global health concerns and strategies to counter it amid ongoing COVID-19 pandemic

“…As a result, they are not counted in the total tally. While studying the transmission dynamics of Omicron in immunocompetent and immunosuppressed populations, it was found that in comparison to other VOCs, asymptomatic carriage is increased to 16% in both people living with HIV and people living with HIV/AIDS in comparison to 2.6% during the Beta and Delta outbreaks ( Garrett et al, 2022 ).…”