Why the delta variant is spreading COVID-19 so quickly — and what that means for Canada

The recent outbreak in the United States has led the US Centers for Disease Control and Prevention (CDC) to recommend that Americans wear masks in areas with high transmission “regardless of vaccination status”.

So why is this particular species spreading so quickly? What is the mechanism behind its apparent success in infecting the human host?

The answers are complex, and there are still unknowns about exactly how the delta variant was able to take hold at such a rapid pace, throwing boldness into the global effort to stamp out the pandemic.

But we’re getting closer to understanding how it works — and why vaccines, fortunately, still hold up.

How contagious is delta?

The delta variant is thought to be significantly more contagious than the early strain of SARS-CoV-2, the virus that first swept the world. The World Health Organization has described Delta as a different concern.

“We are fighting the virus itself but it is a virus that is getting fitter and better adapted to transmission between us humans,” Dr. Michael Ryan, executive director of the World Health Organization’s Health Emergencies Programme, said during a news briefing on Friday.

Scientists estimate it spreads about 50 percent faster than the alpha variant, which was 50 percent more infectious than the original virus strain, According to the Yale School of Public Health.

This means that each infected person is able to pass the virus on to more people than before, helping this variant spread through the population quickly — and even faster among those whose immune systems are not already on high alert due to a previous COVID-19 infection. or vaccination.

Watch | The World Health Organization warns that the COVID-19 delta variant is a ‘dangerous virus’:

Why is it more portable?

While the exact mechanism that makes delta more transmissible is not entirely clear, emerging research is pointing to possible reasons why it is so contagious.

One lab study published in the journal host cell and microbe, from researchers at Kumamoto University and the Weizmann Institute of Science, suggest that mutations on the barbed protein of the SARS-CoV-2 variant can evade cellular immunity and may increase infection.

University of Ottawa epidemiologist Raywat Dionandan explained that the spike protein is an important feature on the surface of the coronavirus that allows it to reach our cells.

“It fits into a receptor in our cells and then gets into the cell through that receptor. Something in the mutation has changed a shape or feature on the spike protein that makes it fit a little bit better,” he said.

As a result, you need fewer viruses to get infected.

Another study from a team in China, which has not yet been reviewed, found that people with the delta variant carry, on average, more than 1,000 times more virus in their nose than the original strain – which likely means they shed more of it.

The researchers also found that people with this variant test positive faster: about four days after exposure, compared to about six for the original strain. This indicates that delta is multiplying at a faster pace inside a person’s body.

“They may actually secrete more viruses which is why they are more transmissible,” microbiologist Sharon Peacock, who directs the UK effort to sequence the genomes of coronavirus variants, told Reuters recently.

How effective are vaccines in protecting against this?

If delta load means people could shed more virus and pass it on to others more easily, vaccines certainly have a harder job — because people’s immune systems are now facing a larger army and need to ramp up to mount a defense.

In the United States, the CDC warned on Friday that Emerging data from a county in Massachusetts notes that higher viral loads may mean vaccinated people can still pass delta to others.

But the good news is that leading-edge vaccines, including those approved for use in Canada, appear to prevent serious illnesses that can lead to hospitalization or death.

A recent study in the New England Journal of Medicine It was found that two doses of the Pfizer-BioNTech vaccine were 88% effective against the delta variant, while two doses of the AstraZeneca-Oxford vaccine were 67% effective.

It was a sign of a decrease in the ability of vaccines to suppress infection of any severity level – whether mild or more severe – when compared to the previous alpha formula, but the researchers said there were only “modest differences”.

Last Data from Israel It also showed that the Pfizer injection reduced the risk of serious illness by a whopping 91 percent, and hospitalization by 88 percent. The level of protection against symptomatic infections was generally less than half that, but there are questions about how the government collects its data and how many infections are involved.

Still, it’s a hopeful, real-world snapshot of how a pioneering mRNA vaccine stave off serious illness, and it’s likely that Moderna’s highly-like shot is also used in Canada in the same way.

“I don’t want to downplay the risks of things like ‘long COVID’, but one of the biggest risks is how likely you are to get seriously ill after being infected,” stressed Angela Rasmussen, a virologist at the University of Saskatchewan Vaccine. and the Infectious Diseases Organization.

“The bottom line here is that vaccination is still very protective,” she said.

How widespread is delta?

This variant has certainly spread around the world since it was first reported in October 2020 in India, with other countries later reporting high levels as well.

“It outperforms all other viruses because it spreads much more efficiently,” Shane Crotty, a virologist at the La Jolla Institute of Immunology in San Diego told Reuters.

In the United States, Delta now accounts for more than 80 percent of new infections. Cases are increasing in many areas with low vaccination rates, and data show that total unvaccinated individuals approach 97 percent of all severe cases.

Across Africa, meager vaccination rates, along with a high delta variable, are putting great pressures on hospital systems in various countries.

The variant has now been found in at least 26 African countries, and 21 countries have seen cases rise by more than 20 percent for at least two weeks, the World Health Organization announced in late July.

Countries from the UK to Singapore are also dealing with delta booms – including Canada. Variants of this virus now make up the bulk of SARS-CoV-2 infections.

By early July, Delta accounted for nearly 70 percent of the country’s cases, according to the most recent full genome sequencing data available from Public Health Canada.

That represents a huge jump since early May, when Delta still accounted for less than 10 percent of serial infections.

So what does all this mean for Canada?

There are now increasing signs that the delta’s rise could lead to another sweeping increase in cases – although nearly six in 10 Canadians have now been fully vaccinated, millions remain unprotected.

Ontario and Quebec have largely stabilized for new daily COVID-19 cases after weeks of declining numbers, while the number New cases reported every day in British Columbia have already tripled During the past three weeks.

virus too It is spreading faster in Alberta from what happened during the height of the county’s third wave — all while that county is set to loosen its strictest restrictions around mask-wearing and isolation requirements.

Watch | Alberta removes most COVID-19 isolation, testing requirements:

Alberta will roll back requirements for COVID-19 testing, contact tracing and quarantine, despite a spike in cases in the province. 2:05

Even if overall case growth begins to pick up, some experts hope that Canada, as a whole, will avoid more serious outcomes, including massive strain on the country’s hospital networks and a similar number of deaths to previous waves.

Rasmussen said most people may still be able to avoid infection if they are vaccinated and play safely, even in high-density urban areas, although she expects outbreaks in schools if mitigation measures are not implemented.

Dionandan said many Canadians are still wearing masks and taking precautions in social settings.

“I am somewhat optimistic that if this good decision continues to be made, we can be world leaders in this endeavour.”