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A health-care worker holds up a sign signalling she needs more COVID-19 vaccines at a mass vaccination facility at the CAA Centre in Brampton, Ont.Nathan Denette/The Canadian Press

When news of the Omicron variant first made headlines late last month, Canadian scientists were desperate for any shred of data that would illuminate what people should expect from a troubling new development in the course of the pandemic.

Just over three weeks later, the information is starting to pour in. Now, the challenge is knowing which results are the most reliable and relevant from a public-health perspective.

“All labs are under pressure right now to produce data,” said Marc-André Langlois, a molecular virologist at the University of Ottawa who heads up Canada’s Coronavirus Variants Rapid Response Network. “You want to make sure that the best possible science is coming through.”

But even given that caveat, there is an emerging profile of the Omicron variant and its projected impact that public-health experts say must be taken seriously. This includes key details about the variant’s transmissibility, its ability to circumvent vaccines and its likelihood of causing severe disease. All three of these in turn feed into the one variable that matters most, which is the rate of hospital admissions because of COVID-19.

Here’s what scientists have learned:

How transmissible is the Omicron variant?

The short answer is: very. While it’s difficult to measure the transmissibility of the variant relative to the original version of the virus, it’s now abundantly clear that Omicron is spreading fast wherever it goes. Several factors are likely behind this, including the fact that Omicron is less hindered by vaccines and can spread more easily through a vaccinated population than other variants.

But there is also early evidence from a multicentre study led by Swiss researchers that shows the variant has elevated affinity for the ACE2 receptor that is the coronavirus’s docking point on host cells. The study, posted online on Tuesday, has not yet been peer-reviewed.

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Whatever the reason, the practical outcome is that the effective reproduction number of the virus – the average number of cases expected to arise by transmission from a single case – is more than three and possibly more than four.

This range far exceeds the equivalent number for the Delta variant and, because of the power of exponential growth, that translates into a doubling of case numbers about every 2.5 days, based on an estimate by the UK Health Security Agency. In Canada, that means Omicron is on track to become the dominant variant of the coronavirus as early as this month.

“The growth rate of this variant is really, truly shocking,” said Jason Kindrachuk, a medical microbiologist at the University of Manitoba. “We have to adapt as the virus is adapting.”

How much does Omicron compromise vaccines?

Omicron carries more than three times the genetic mutations that other variants exhibit. This means it looks different to the antibodies generated by vaccines to fight the virus. At least half a dozen lab studies have now provided scientists with a measure of the degree to which Omicron can evade those “neutralizing” antibodies.

Broadly speaking, those studies show the ability of antibodies to neutralize the variant and prevent infection has been reduced by a factor of 20 to 40. In a situation where many Canadian adults and teens are reaching the six-month points after their second doses and are likely to have waning antibody levels, this means the possibility of breakthrough infections is far higher than has been seen so far with Delta.

The good news is that antibodies are only one aspect of any individual’s immune-system arsenal. Even if an infection begins, for those who are vaccinated it’s still likely that other immune cells will start to recognize those parts of the coronavirus that haven’t mutated, allowing immune cells to swing into action.

“It’s kind of like a boxer in a ring who has taken a hit,” said Jennifer Gommerman, an immunologist at the University of Toronto. “They’re up against the ropes and they’re kind of shaking their head but they’re going to get up and get back into the fight.”

So far, vaccines are appearing to hold up against severe disease, but the new variant’s presence underscores the need for those who are eligible to receive third doses to raise their immunity as much as possible. Meanwhile, those who are still unprotected by vaccines now face a variant that can move among the vaccinated population and find them.

What about disease severity?

One study that drew plenty of media attention on Wednesday was conducted by researchers at the University of Hong Kong. Working with tissue samples, the study team found that Omicron was able to multiply at 70 times the rate of other variants in the bronchus – the part of the airway that lies at the entrance to the lungs. Yet its multiplication rate was only one tenth that of the Delta variant in lung tissue. Since infections in the lungs are more likely to lead to severe disease, the results may help explain why Omicron has been associated with fewer severe outcomes, based on a large South African population study reported earlier in the week.

But, while scientifically interesting, neither of these studies has been peer-reviewed. Dr. Langlois cautioned that hopes for a less deadly illness are no cause for complacency. Modelling by the Canadian network shows that the ability of Omicron to cause severe disease would have to be lowered by a factor of 10 to prevent a higher rate of hospital admissions than has been seen in the pandemic to date. The unlikelihood of that scenario – reinforced on Friday by a report from researchers at Imperial College London that found no evidence of lower severity in Omicron – implies the need for stronger public-health measures.

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