Delta Variant is More Deadly and Contagious Than Experts First Thought

Canadian research shows that the Delta variant among COVID patients is significantly a more deadly wave and more virulent than what experts thought.

A modelling for Australia's path out of the pandemic made experts at the Doherty Institute assume that Delta was more contagious, but not more virulent than Alpha. However, future forecasts of 'normality' remains hazy but will reflect new understanding of how serious the Delta variant is.

Professor James McCaw from the University of Melbourne who also works with the Doherty Institute said that assumption would change.

"We made an agreed and very deliberate assumption that it was Alpha-like," he said. "And, of course, as scientists we update our understanding based on available evidence, and it's now far clearer that Delta is more severe."

New evidence changes the equation

Original assumption was that 'the Delta variant might cause more severe illness than previous variants in unvaccinated people' as what United States' Centers for Disease Control and Prevention publicly cited. This is also a widely adopted view from University of Toronto research and Burnet Institute modelling.

However, Professor McCaw said all these were made on the evidence available at the time.

"At the time that the Doherty work was done, it was very clear that Delta spread more quickly, and that is, of course, incorporated in the work," he said. "But evidence that Delta was more severe in terms of clinical outcomes was either scant, or certainly unsettled in the international community."

According to the professor, the Doherty Institute provides ongoing advice to governments on reopening, including the new assumption.

"Forecasts of potential hospitalizations, when we get to that stage, would account for the increased severity of Delta. So, we always are updating our views and updating our advice accordingly."

Infectiousness of the Delta variant

It still remains a fact that Delta may more likely put patients in intensive care, and more infectious on older people.

"Unfortunately, all studies have shown the equivalent of a doubling of hospitalisation across all age groups for Delta," says Epidemiologist Catherine Bennett from Deakin University who already saw early signs.

"But [the Canadian study] also breaks it down further and shows that actually, if you're hospitalized, you're even more likely to end up in the ICU with Delta, than with other variants."

Professor Bennett added that it is impractical to wait until the Canadian research is peer-reviewed, and that "it looks like a very solid retrospective study", given that it is "consistent with the other studies that have been going through peer review, and many which are now fully peer-reviewed, that tell the same story."

Moreover, experts say vaccinating parents is the best way to stop COVID-19 infection among children.

"A lot of kids that we see getting infected, they get infected by the parents in the home," says Professor Nick Golding from Curtin University, also working with the institute. He suggested that adding children to vaccination thresholds could inflate vaccination rates, as young people are very used to getting vaccinated.