When COVID-19 first emerged, the mystery surrounding what was causing the disease and how it was being transmitted incited fear and confusion around the world. An unprecedented global research effort has since provided clarity on these matters, but important questions like how long the virus remains infectious and what causes severe disease remain.
“A clearer understanding of disease pathogenesis is necessary to support the development of risk stratification tools, improve limited medical resource allocation and develop novel or re-purpose existing therapeutics which target critical pathways in the COVID-19 inflammatory cascade,” said Lisa Ng, a Senior Principal Investigator at A*STAR’s Singapore Immunology Network (SIgN) and Executive Director of the A*STAR Biomedical Research Council (BMRC).
With other members of the Singapore 2019 Novel Coronavirus Outbreak Research team, an interdisciplinary group of researchers from various institutions across the country, Ng and Executive Director of A*STAR’s Infectious Diseases Laboratories Laurent Renia conducted a comprehensive study to better understand COVID-19 and improve management of the disease. “Our findings on the virus have implications on identification, patient triage and transmission control measures,” he said.
To design effective transmission control measures, it is important to know how long the virus remains infectious. While most studies have looked at the number of days the virus remains viable after infection, Ng and her team found that a proxy value called the cycle threshold, or Ct value, may also be useful.
The Ct value describes the number of cycles needed to detect the virus in a polymerase chain reaction test, the gold standard test used to detect SARS-CoV-2. Viable virus was only detected at a Ct value less than 30, or in samples collected less than 14 days after symptoms first emerged. However, Ng cautioned that additional studies are needed in more patients—including asymptomatic cases—before the Ct value can be widely used as an indicator.
The study also looked at the link between disease severity and the appearance of antibodies and inflammatory signals across time. The researchers found that patients with severe symptoms develop antibodies earlier and at higher concentrations than those with mild symptoms, knowledge that can be used to predict which patients may develop severe disease.
What’s more, severe cases had higher levels of several proinflammatory signals and growth factors. This implies that already available drugs that target and inhibit these signals could be repurposed to treat patients with severe COVID-19, Ng said.
The team is now monitoring patients throughout both disease and recovery to better understand changes in the immune response with time.