Evidence of co-infection during Delta and Omicron variants of concern co-circulation, weeks 49-2021 to 02-2022, France (preprint)

We report evidence of Delta/Omicron SARS-CoV-2 co-infections during the fifth wave of COVID-19 pandemics in France for 7 immunocompetent and epidemiologically unrelated patients. These co-infections were detected by PCR assays targeting SARS-CoV-2 S-gene mutations K417N and L452R and confirmed by whole genome sequencing which allowed the proportion estimation of each subpopulation. For 2 patients, the analyses of longitudinal samples collected 7 to 11 days apart showed that Delta or Omicron can outcompete the other variant during dual infection.

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.