Clinical phenotypes and outcomes associated with SARS-CoV-2 variant Omicron, sublineages BA.1, BA.1.1, BA.2 and impact of mutational patterns in critically ill French patients with COVID-19 (preprint)

Infection with SARS-CoV-2 variant Omicron is considered to be less severe than infection with variant Delta, with a rarer occurrence of severe disease requiring intensive care. However, a substantial number of patients infected with variant Omicron still experienced severe COVID-19. Little information is available on comorbid factors, clinical conditions and specific viral mutational patterns associated with the severity of variant Omicron infection. In this multicenter prospective cohort study, patients consecutively admitted for severe COVID-19 in 20 participating intensive care units in France between December 7th 2021 and May 1st 2022 were included. Among 259 patients for whom SARS-CoV-2 variant lineage was determined, we show that the clinical phenotype of patients infected with variant Omicron (n = 148) was different from that in those infected with variant Delta (n = 111). We observed no significant relationship between Delta and Omicron variant lineages/sublineages and 28-day mortality (adjusted odds ratio [95% confidence interval] = 0.68 [0.35–1.32]; p = 0.253). Among Omicron-infected patients, 43.2% were immunocompromised, most of whom had received two doses of vaccine or more (85.9%) but displayed a poor humoral response to vaccination (mean difference in serum anti-spike IgG antibody titers between vaccinated and non-vaccinated immunocompromised patients: 1078 BAU/mL [-319.4; 2475.0]; p = 0.160). The mortality rate of immunocompromised patients infected with variant Omicron was significantly higher than that of non-immunocompromised patients (46.9% vs 26.2%; p = 0.009). In patients infected with variant Omicron, there was no association between specific sublineages (BA.1/BA.1.1 (n = 109) and BA.2 (n = 21)) or any viral genome polymorphisms or mutational profile and the 28-day mortality.

Epidemiological and clinical insights from SARS-CoV-2 RT-PCR cycle amplification values (preprint)

The SARS-CoV-2 pandemic has led to an unprecedented daily use of molecular RT-PCR tests. These tests are interpreted qualitatively for diagnosis, and the relevance of the test result intensity, i.e. the number of amplification cycles (Ct), is debated because of strong potential biases. We analyze a national database of tests performed on more than 2 million individuals between January and November 2020. Although we find Ct values to vary depending on the testing laboratory or the assay used, we detect strong significant trends with patient age, number of days after symptoms onset, or the state of the epidemic (the temporal reproduction number) at the time of the test. These results suggest that Ct values can be used to improve short-term predictions for epidemic surveillance.