Doug Manuel

Dr. Doug Manuel, MD

Director, CoVaRR-Net Wastewater Surveillance Research Group
Deputy, CoVaRR-Net, Public Health, Health Systems and Social Policy Impacts Pillar
Senior Scientist, Ottawa Hospital Research Institute
Distinguished Professor, University of Ottawa

Sarah (Sally) Otto

Sarah Otto, PhD

Co-Lead, CoVaRR-Net Computational Analysis, Modelling and Evolutionary Outcomes (CAMEO) Pillar
Canada Research Chair in Theoretical and Experimental Evolution, and Killam University Professor, University of British Columbia

How concerned should Canadians be about the Omicron subvariant known as BA.2?

Is the perception that BA.2 is highly contagious but doesn’t endanger our health accurate, or do Canadians need to respond by choosing appropriate precautions to mitigate a serious threat and stay healthy? The answer from CoVaRR-Net experts is the latter. Due to its high transmissibility and rapid spread as public health measures have been reduced, BA.2 is fueling the sixth wave of the pandemic and increasing both the health risks for Canadians and the need for thoughtful, appropriate protections.

BA.2 is much more transmissible than BA.1 and seized “market share” fast

The BA.2 subvariant is more transmissible than the BA.1 subvariant (the first Omicron variant that was dominant from December to February), so it infects people more readily and puts them at higher risk of developing COVID-19. “Both modelling and household transmission indicate that BA.2 is better able to spread, doubling in frequency here in Canada every 8-10 days, relative to the frequency of BA.1, which in turn was much more transmissible than Delta. BA.2 can better infect and replicate in our cells, allowing the virus to jump from person to person more easily,” says Dr. Sarah Otto, CoVaRR-Net’s Computational Analysis, Modelling and Evolutionary Outcomes (CAMEO) Pillar Co-Lead, Killam University Professor at University of British Columbia and Canada Research Chair in Theoretical and Experimental Evolution.

BA.2 has a strong selection advantage, which enabled this variant to capture “market share” at an accelerated pace and almost entirely replace BA.1. “BA.2 is now the overwhelmingly dominant strain in Canada, representing more than 70 per cent of cases, and has become the dominant variant globally,” says Dr. Otto.

BA.2 has triggered a spring wave of rising infections and hospitalizations

The fact that BA.2’s high transmissibility and very strong selection advantage comes at a time when public measures were lifted across the country has not helped. “We’re seeing a steep rise in infections in wastewater surveillance signals in locations across Canada and increased positivity rates. Infections are rising and projected to keep climbing. Hospitalizations are increasing due to the growing number of infections and one of the biggest risks is that hospitalizations will go even higher than projected last month from models,” says Dr. Doug Manuel, CoVaRR-Net’s Public Health, Health Systems and Social Policy Impacts Pillar Deputy and Director, CoVaRR-Net Wastewater Surveillance Research Group.

Health risks rise

The levels of COVID-19 found in wastewater today in Canada at an increasing number of sites are comparable to those seen during the winter BA.1 Omicron wave in which over 7,000 Canadians died. So, although there may be perceptions that BA.1 and BA.2 are “milder” than the Delta variant and that the health risks from COVID-19 are diminishing or have passed, BA.2 remains a serious threat that is causing Canadians to suffer severe disease, hospitalizations, and deaths every day.

The long-term effects of more infections cannot yet be ascertained, but as more people develop COVID-19, more people are also likely to suffer from long-COVID. This will increase the subsequent strain on the healthcare system and the economy, with a loss of productivity and more absenteeism.

The risks of severe disease, hospitalization, and death from BA.2 have increased particularly for unvaccinated and incompletely vaccinated Canadians, and people who are immunocompromised or more vulnerable because of their age:

  • While more than 85 per cent of Canadians aged 5 and older have received two doses of vaccine, only 57 per cent of Canadians 18 and older have received three doses.
  • Less than 40 per cent of Canadians from 5 to 11 years old have received two doses.
  • A person who has received a booster (third dose) is almost seven times less likely to be hospitalized for COVID-19 than an unvaccinated person and six times less likely to die.

Third and fourth doses also offer much greater protection against severe disease from BA.2 than do two doses and are a vital safeguard for anyone who received a second dose last fall or earlier since COVID-19 immunity wanes over time. “If you have two doses, you are incompletely vaccinated against BA.2 and you need an additional vaccination to protect you. Take the vaccine offered to you and you are less likely to become ill,” advises Dr. Manuel.

In addition to how many doses, it matters how long ago you had those doses, especially in protecting people from infection in the first place. Right after a third or fourth dose, antibody levels in the body skyrocket, allowing the body to better fight off infections. This immune response generates really robust (20-30x) protection from hospitalization, but this protection wanes over time, especially with the genetically distinct Omicron variant (BA.1 and BA.2). “By about four months, we’re seeing that protection fall again, which is why we recommend an additional dose to anybody with a health vulnerability as soon as they are eligible,” advises Dr. Manuel.

Take precautions to protect Canadians who are most susceptible

When deciding whether to wear a mask, it’s also important to consider the health status of the people around you “People need to take responsibility to protect those around them who are vulnerable because of lower or compromised immunity. You might not be aware of their immune status because it is an invisible disability,” says Dr. Manuel.

Because BA.2 is so contagious and can more easily cause severe disease in people with a weaker immune system, Canadians who are older or immunocompromised need additional safeguards through additional vaccine doses (if eligible) and precautions taken by the people around them. “A big concern in the current BA.2 wave is the increased risks for the most susceptible populations, older and immunocompromised Canadians who have less protection against hospitalization because of their waning immunity. For these vulnerable populations, the risk of being hospitalized during this BA.2 wave is 2-3 times as high as in the first BA.1 Omicron wave unless they receive another dose. An essential goal in the current wave is to protect people who are most at risk of developing severe disease, going into hospital, and dying from COVID-19,” says Dr. Otto.

Blunt the wave through vaccination, masks, and rapid tests to reduce transmission

Whether to get vaccinated, wear a mask in crowded indoor spaces, and do rapid testing (which can be hard to access for some people) when appropriate will make a difference in the trajectory of the spring BA.2 wave and the number of Canadians whose health is adversely affected.

“Everybody plays a role in reducing transmission. We are in another wave and if enough people take their masks off, the wave will be a lot higher. It’s not just about wearing a mask for your own protection, but masks also protect others by reducing the amount of virus in the air, especially since many people don’t realize they’re infectious. We appeal to the good judgement of people to wear masks in crowded spaces and get vaccinated with the third dose, or the fourth dose, if they need it,” says Dr. Otto, noting that businesses could also help by offering safe shopping days where customers know that masks will be worn by all customers and by investing in better ventilation systems to protect customers.

View modelling done by Dr. Caroline Colijn, CoVaRR-Net’s Computational Analysis, Modelling and Evolutionary Outcomes (CAMEO) Deputy, showing an estimated rise in infections from BA.2 with and without public health measures.


  1. Public Health Agency of Canada.
  2. Public Health Agency of Canada. COVID-19 vaccination coverage in Canada –
  3. Public Health Agency of Canada. COVID-19 vaccination coverage in Canada –
  4. Public Health Agency of Canada.

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