Ciriaco Piccirillo

Dr. Ciriaco Piccirillo

Immunology & Vaccine Protection Pillar Co-Lead, T cell responsesProfessor and Graduate Program Director, McGill University
Senior Scientist, Research Institute of the McGill University Health Centre

Dr. Cory Neudorf

Public Health, Health Systems and Social Policy Impacts Pillar Co-Lead
Interim Senior Medical Health Officer,, Saskatchewan Health Authority
Professor, University of Saskatchewan

Cases of Omicron rose rapidly over the holidays and, since then, it has become the dominant variant.

When it was first identified in November 2021, doctors feared the worst. With numerous mutations that could help the virus evade the vaccines’ targets, many researchers predicted Omicron was going to significantly increase the number of people infected with SARS-CoV-2, the virus that causes COVID. “The world was holding its breath because this thing was spreading three to four times more quickly than the other variants,” said CoVaRR-Net’s Ciriaco Piccirillo, who is also a Senior Scientist at the Program in Infectious Diseases and Immunity in Global Health at Research Institute of the McGill University Health Centre.

The predictions of high transmissibility have proven to be true.

Omicron appears to be less virulent than expected for those double- and triple-vaccinated

“Where you live, your underlying health and your vaccine status will determine how Omicron is going to affect you,” says CoVaRR-Net’s Cory Neudorf, a professor and researcher in the Department of Community Health and Epidemiology at the University of Saskatchewan.

“Even though we’re getting more breakthrough infections, it’s less severe in people who’ve been immunized fully, leading to a less severe clinical picture.”

There has been a reduction in hospitalizations among the vaccinated, immunocompetent individuals who have contracted Omicron, and many have experienced less severe symptoms than Delta. However, unvaccinated and vulnerable groups like older adult and those with immunodeficiencies remain at a significantly higher risk of developing serious complications due to COVID-19.

“For the unvaccinated or the not-optimally-vaccinated, the virus is more likely to walk down the path of causing severe disease,” says Piccirillo.

With the unvaccinated continuing to face the high likelihood of developing severe symptoms that require hospitalization, and the higher transmissibility of Omicron even in the vaccinated populations, medical facilities have been stretched beyond capacity.

Why Omicron shows less virulence than the previous variants of concern

Omicron is normally found in the upper respiratory tract and has typically shown an inability to infect a person’s lungs, even among some of the more vulnerable populations. That could explain why runny noses have accompanied this variant, something we did not see with Delta or the ancestral virus.

“An overarching evolutionary feature for many viruses of this type is that their survival depends on their capacity to enter our systems but not kill our systems. I suspect that we’re going down that path,” said Piccirillo.

What we can do to ensure lower numbers of infections

“We need to keep high proportions of the population fully immunized and continue the wearing of masks, distancing and improving ventilation,” says Neudorf. “All of those things can help reduce the likelihood of outbreaks happening in schools, coupled with rapid antigen testing in households so that kids can be kept home if they are positive.” He adds that widespread adherence to gathering restrictions and short-term closures will keep numbers down to a level where it’s not straining the healthcare system.

Both Neudorf and Piccirillo add that if we want to avoid new variants and subsequent waves of the pandemic, we need to also make sure Canada and others in the West help impoverished countries raise their vaccination levels. They say they need to have the abilities to distribute, access and deploy vaccines into their local communities.

To arrange an interview with Dr. Ciriaco Piccirillo or Dr. Cory Neudorf, please contact: