CMB graduate student Hannah Despres, right, and Assistant Professor of Microbiology & Molecular Genetics Emily Bruce, Ph.D., in Bruce's Lab in UVM's Stafford Building.

Understanding how variants function allows public health leaders to develop more effective prevention strategies against SARS-CoV-2. In a new study in the journal PNAS, a team of University of Vermont and University of Washington scientists discovered that – based on clinical samples from infected individuals – the Delta variant had a higher infectivity than the Alpha variant of COVID-19.

Senior author Emily Bruce, Ph.D., a University of Vermont assistant professor of microbiology and molecular genetics, and colleagues from the University of Washington and Fred Hutchinson Cancer Research Center, sought to determine “if the ratio between viral RNA and infectious virus levels was changing given the high levels of Delta transmission we saw over the summer,” says Bruce.

The group was surprised by their findings.

“What we saw was that people infected with Delta had almost six times more virus in their nasal swab samples than people infected with Alpha for the same amount of RNA,” says first author and UVM graduate student Hannah Despres.

For this study, the team measured a set of 162 clinical samples containing SARS-CoV-2 Alpha, Delta, and Epsilon variants, collected in identical swab kits from outpatient test sites and processed soon after collection. The researchers measured the amount of viral RNA and the infectious viral titers for each sample, and showed that virus produced from people infected with Delta was six times more infectious than Alpha for the same ‘viral load’ of RNA.

Gaining a better understanding of the biological traits of the variants allows scientists to more quickly and accurately assess new variants for infectiousness and severity of disease, explains Despres.

“This research is of immediate and practical importance for public health officials,” says Jan Carney, M.D., M.P.H., associate dean for public health and health policy at UVM’s Larner College of Medicine. “More infectious variants warrant increased prevention measures and messaging, such as the need for highly-effective booster shots, indoor masking, and testing. Having specific knowledge about current and future variants increases our ability to anticipate and respond, best protecting patients and the public.”

“We hope to continue this work and start unpacking how this increased infectivity is happening on a mechanistic level, and also to investigate how much this may play a role in the infectivity of other SARS-CoV-2 variants,” says Bruce, whose team is already examining characteristics of the Omicron variant.