A Canadian study has linked the new variants of SARS-CoV-2, particularly the Delta variant, to an increased risk of severe disease and death.

The University of Toronto issued a study in the Canadian Medical Association Journal (CMAJ) on 212,326 cases in Ontario from February to June 2021. The study compared the risks of hospitalization, ICU admission, and death from the VOCs with those risks from non-VOC SARS-CoV-2 strains.

The researchers concluded that Alpha, Beta, and Gamma variants have a mutation that increases transmission, while Delta has a mutation that increases its ability to replicate.

Increased risk from the Delta variant

The 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, the infectious diseases specialist at the Vanderbilt University Medical Center in Nashville, TN, noted that while it is well recognized that Delta is more contagious than other virus variants, this new study strongly reinforces the finding that it also causes more severe disease.

Vaccination reduces the risk, but precautions are still important

In the meantime, the study brought some positive news; vaccination, partial or complete, does reduce the risk of severe disease and death from all the VOCs. During the course of the study, while vaccination numbers were increasing, hospitalizations, ICU admissions, and deaths were decreasing.

“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,” according to Schaffner.

Dr. Kirsten Patrick, interim editor-in-chief of the CMAJ, observed that most COVID-19 patients who required critical care were unvaccinated, and "we need to be smarter than the virus, by taking all available precautions to avoid future lockdowns." She advised governments to continue with measures such as extending vaccine mandates and passports, ensuring global vaccine delivery, and continuing to identify, track, and control outbreaks.