Written by Katharine Lang — Fact checked by Alexandra Sanfins, Ph.D.
A Canadian study has found a link between the new variants of SARS-CoV-2, particularly the Delta variant, and an increased risk of severe disease and death.
The retrospective study, by the University of Toronto and appearing in the Canadian Medical Association Journal (CMAJ), looked at 212,326 cases in Ontario from February 7 to June 27, 2021. The study authors compared the risks of hospitalization, ICU admission, and death from the VOCs with those risks from non-VOC SARS-CoV-2 strains.
The researchers screened the cases for Alpha, Beta, Gamma, and Delta VOCs. Non-VOC infections made up 22.4% of the cases. More than three-quarters of the cases were Alpha, Beta, or Gamma, while 2.8% were probably Delta.
Alpha, Beta, and Gamma variants have a mutation that increases transmission, while Delta has a mutation that increases its ability to replicate.
The authors note that before May 2021, there was no routine screening for the Delta variant, so it is likely that the numbers underestimate the prevalence of this variant.
Increased risk from the Delta variant
The present study found that all VOCs increased people’s risk of hospitalization, ICU admission, and death due to COVID-19.
However, the highest risks were from the Delta variant. In the Delta cases, there was a 108% increase in the risk of hospitalization, a 235% increased risk of ICU admission, and a 133% higher risk of death, compared with the original variant.
These effects were present even when the researchers adjusted the data for factors such as age, sex, vaccination status, and comorbidities.
Prof. William Schaffner, infectious diseases specialist at the Vanderbilt University Medical Center in Nashville, TN, commented:
“This important study from Canada reinforces the serious impact the Delta variant is having. It is well recognized that Delta is more contagious than other virus variants. This new study convincingly reinforces the finding that it also causes more severe disease.”
The Delta variant is now the dominant variant in the European Union, the United Kingdom, and the United States.
The findings of the present study corroborate those of the studies in England, Scotland, and Singapore that have also shown increased risks from the Delta variant.
Speaking to Medical News Today, Dr. Christopher Coleman, assistant professor of infection immunology at the University of Nottingham in the U.K., highlighted the international relevance of the study.
He said, “Although this [Canadian] study has some limitations, as acknowledged by the authors, this is exactly the kind of study that helps ‘build a picture’ by showing that similar observations can be observed in a lot of different circumstances.”
“It is not something unique about the U.K. that means the Delta variant is associated with more dangerous infections only here,” he added.
Some good news from this study is that vaccination, both partial and complete, reduced the risk of severe disease and death from all the VOCs. During the course of the study, as vaccination numbers increased, hospitalizations, ICU admissions, and deaths decreased.
“These results from Canada now add to those from studies from England, Scotland, and Singapore, all showing that Delta infection causes more severe disease. Fortunately, our currently available vaccines continue to provide good protection against severe Delta infections.”
– Prof. William Schaffner
The authors highlight that these VOCs have led to a pandemic that is “larger and more deadly” than it would otherwise have been.
Dr. Kirsten Patrick, interim editor-in-chief of the CMAJ, observed that most COVID-19 patients who required critical care were unvaccinated, but said, “The virus has become smarter and more dangerous, which means that we need to be smarter too.”
She stressed that we “must use all the tools at our disposal to prevent future lockdowns.” As well as boosting vaccination rates, governments must continue with measures such as extending vaccine mandates and passports, ensuring global vaccine delivery, and continuing to identify, track, and control outbreaks.