How is Omicron spreading so fast? The virus could now multiply 70 times faster in the respiratory tract

Researchers found that, just 24 hours after infection, Omicron multiplied 70 times faster than the Delta variant or the original SARS-CoV-2 virus in tissue samples from human bronchial tubes – the two large tubes that carry air from your windpipe to your lungs. .

It’s a finding that could explain why Omicron appears to be transmitted faster between humans than previous variants, and stands in stark contrast to how the variant replicated in the team’s actual lung tissue samples. research in relation to the bronchi. In these lung samples, the variant multiplied at a rate more than 10 times slower than the original virus.

It is the lungs – not the bronchi – that are linked to life-threatening complications of COVID-19 such as pneumonia and, in severe cases, acute respiratory distress syndrome or ARDS. So, if these findings hold true in a real-world context, the team suspects that slower replication in the lungs could mean reduced disease severity.

The observation also echoes early evidence from South Africa suggesting that Omicron may be linked to a milder course of the disease.

But the severity of the disease is not only a function of where and how quickly a virus replicates in a certain organ, “it is also a function of our immune response,” said Dr Dominik Mertz. , an infectious disease specialist at McMaster University in Hamilton, in an email exchange with CBC News.

People need to be careful when drawing direct conclusions from lab studies about how infections will actually look in the real world, he wrote.

“The latter needs to be based on observations in those with confirmed infections, and we still need to learn more in terms of actual severity in a population like ours that has mRNA vaccine immunity first and foremost.”

The Omicron threat is probably “very important”

The Hong Kong lead researcher – Dr Michael Chan Chi-wai, associate professor in the university’s school of public health – also acknowledged that the severity of the disease is related to other factors, such as whether the system A person’s immune system goes haywire in response to a coronavirus infection in what is called a “cytokine storm”.

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“It is also noted that by infecting many more people, a highly infectious virus can cause more serious illness and death even though the virus itself may be less pathogenic,” he said in a statement.

“Therefore, together with our recent studies showing that the Omicron variant can partially evade immunity from vaccines and past infections, the global threat of [the] The Omicron variant is likely to be very important. “

Ryan Troyer, virologist and researcher at Western University in London, Ont., Stressed that the Hong Kong team’s results are still preliminary.

“The differences they find here seem pretty significant,” he said. “It will be interesting to see if this is supported by further studies.”

Variety of symptoms, from mild to severe

Troyer also noted that the study adds to the growing pile of evidence that COVID-19 infections can present in a variety of ways, even before the rise of the Omicron variant, with symptoms ranging from severe and potentially fatal to much lighter and perhaps barely noticeable.

Take the ongoing testing of professional sports teams like the NBA and NHL, for example. Troyer said these tests often detect infections in healthy young players that the athletes themselves haven’t even noticed, as vaccination status, age of those infected and other factors all play a role. in the severity of the disease.

a tuesday presentation of Discovery Health, South Africa’s largest private health insurance administrator, offered an analysis of an Omicron outbreak using more than 200,000 COVID-19 test results.

The team noted that for patients with Omicron who required acute care outside of a hospital, the incubation period is typically only three to four days, with patients recovering within days after that. – a shorter period than the previous estimated incubation period ranging from one to 14 days.

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How Boosters Protect Against Omicron

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“The most common early symptom seems to be a scratch or sore throat,” Dr Ryan Noach, CEO of Discovery Health, said during the presentation.

Nasal congestion and a dry cough are also commonly reported, he continued, along with muscle aches or pains manifesting in different areas. “Particularly in lower back pain, which appears to be a hallmark of out-of-hospital presentation,” he said.

Such mundane symptoms are easy to ignore, but experts say this is one of the many ways a more transmissible variant could spread – both quickly and silently.

“I think it’s important for people to think about the fact that you can’t assume that no symptoms mean no virus,” Troyer said.