Study shows high proportion of Omicron infections are asymptomatic

1 July 2022

Initial findings of the Ubuntu trial highlighted the high proportion of Omicron infections that were asymptomatic. The study, “High Asymptomatic Carriage with the Omicron Variant in South Africa”, was published in the journal Clinical Infectious Diseases.

CAPRISA is contributing to the COVPN 3008 study, a multicenter Phase 3 clinical trial in sub-Saharan Africa, which is testing the efficacy of the Moderna vaccine among persons with and without HIV. The trial is also investigating the impact of persistent viral replication among immunocompromised  populations, in terms of viral evolution of further variants of concern, explained lead author and Head of Pathogenesis and Vaccines, Dr Nigel Garrett. 

The study results showed a 23% asymptomatic SARS-CoV-2 Omicron carriage rate in January 2022. Baseline nasal swab data were available for 719/1172 (61.3%) enrolled participants and 162 (23%) had asymptomatic SARS-CoV-2 infection by RT-PCR. SARS-CoV-2 infection was more frequent among SARS-CoV-2 seronegative (95/317) compared to seropositive (67/402) participants, regardless of baseline HIV status (30% vs 17%, p <0.001). 

SARS-CoV-2 infection was detected among 51/153 (33%) persons with HIV (PWH) with a CD4 count <500 cells/mm3 versus 66/354 (19%) of PWH with CD4 counts ≥500 cells/mm3 (p <0.001) (Figure 1), an association seen in both SARS-CoV-2 seropositive and seronegative PWH.

Importantly, many of these asymptomatic carriers had high nasal viral titers, as indicated by the relatively low RT-PCR cycle threshold values. The high prevalence of cryptic carriage of Omicron helped explain its rapid and widespread dissemination globally. 

For further reading see: Garrett N, et al. Clinical Infectious Diseases 2022. doi: 10.1093/cid/ciac237.

Figure 1:  A, Percent of PWH positive for SARS-CoV-2 PCR (blue) among those with CD4 + T-cell counts ≥500 and <500 cells/mm3. 

B, Probability of PCR positivity by CD4 + T-cell count among PWH. Dots display observed data in baseline seronegative (purple) and seropositive (green) asymptomatic study participants