Global COVID-19 cases dropped by half, and experts are looking for explanations

As the number of new coronavirus infections in Canada continues to decline, a similar phenomenon is developing in many other parts of the world, leading experts to better understand why COVID-19 cases are currently declining.

Stronger measures for public health, stricter compliance with the rules for fear of more rapidly spreading variants, and the natural seasonality of coronaviruses may play a role, observers say. In countries with relatively high vaccination and infection rates, such as the United States and Britain, immunity can also slow the spread.

In the last six weeks, the number of new coronavirus infections worldwide has dropped by almost half, from about five million in the first week of January to about 2.7 million last week. According to the World Health Organization, the highest daily case studies worldwide are the lowest since October.

Canada is part of the trend. In the country, new infections increased from 57,519 in the beginning of January to 20,776 in the past week – a decrease of 64 percent.

“We need to understand what drives the transmission dynamics,” Mike Ryan, head of the WHO’s health emergency program, told a news conference on Monday. ‘Is it the natural seasonality and wavy pattern of the disease? Are we building a level of immunity in the population that prevents the disease from finding the next case? And do controls have an impact on it? I think all of the above is true to some extent. ”

As scientists try to decode the downward trend in overall cases, they do so against the background of an increase in infections caused by more contagious variants of SARS-CoV-2 that threaten to usher in a third wave of the pandemic.

“The problem we face is that when you get a drop like this, you will relax the measures,” said Gerald Evans, chair of the Department of Infectious Diseases at the medical school at Queen’s University. “It puts you in danger.”

One explanation for the decline in business is easy to notice by comparing the business curves of countries celebrating Christmas. Put the cards down on top of each other and their winter peaks come together on January 10 and January 11, two weeks after families and friends gathered for the festive season, regardless of the rules in their respective countries.

The heights of the peaks vary from place to place, but Canada, the United States, Britain, Ireland, South Africa, Brazil, Russia and most of Europe saw a boom after the holidays, followed by a decline in the cases. (The rise after the holidays is not so noticeable in major European countries, including France, Italy, Spain and Germany, where the cases also peaked in late November and early December.)

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In countries where Christmas and the post-holiday boom were particularly strong, governments introduced strict social measures that led to an equally sharp drop in cases. This was especially true in Britain, Ireland and South Africa, three countries where new, faster-spreading variants of SARS-CoV-2, the virus that causes COVID-19, have supplanted an earlier version of the virus.

‘They had big, strict closures and reactions. And I think people were terrified of this new variant, ”said Ian Michelow, a pediatrician for infectious diseases and a professor at Brown University, originally from South Africa. ‘It’s a ghost that is very worrying to people, and rightly so. There is no doubt about it. These are more dangerous viruses [because] they spread more easily. ”

Another puzzle could be the natural seasonality of SARS-CoV-2, said Matthew Binnicker, director of clinical virology at the Mayo Clinic in Minnesota. The six seasonal coronaviruses, which cause mild colds, tend to peak in winter and early spring, according to six years of Mayo Clinic data recently published last summer.

“We knew this winter was going to be very difficult, because [SARS-CoV-2] is a respiratory virus, such as influenza, like other coronaviruses, ‘said Dr. Binnicker said. In the Northern Hemisphere, flu usually rises in December, reaches early to mid-January and falls by mid-February. “And that’s really what we saw with COVID,” said Dr. Binnicker said.

It can be difficult to unravel all the reasons why respiratory viruses thrive in winter. SARS-CoV-2 has been shown to survive longer in colder temperatures. Dry air holds viral particles up longer, making it easier to breathe. Some studies have suggested that breathing cold, dry air affects the mucous membranes in the nostrils in a way that lowers their defenses against viruses.

But Peter Juni, scientific director of Ontario’s COVID-19 scientific advice table and professor of medicine and epidemiology at the University of Toronto, says the likely explanation is that when the weather gets cold and dark, people congregate in poorly ventilated indoor spaces where respiratory viruses spread easily.

According to him, the recognition of a seasonal effect of the decline in COVID-19 cases is a pipe dream.

It is also the idea that immunity – whether through vaccination or infection – makes it more difficult for the coronavirus to find Canadian victims, said Dr. June said.

With only 3.4 vaccine doses injected for every 100 Canadians and less than 900,000 infections confirmed since the onset of the pandemic in Canada, the vast majority of Canadians remain susceptible to the coronavirus.

In the United States, however, it’s possible ‘that edge immunity is contributing to the decline in cases, especially in cities that have suffered devastating waves in previous waves, said Jennie Lavine, a biologist at Emory University in Atlanta. “It’s not where I would put my money, but it’s not unthinkable.”

Either way, something works for the U.S.: the country reported just over 55,000 COVID-19 cases on Monday, at a high of nearly 300,000 in one day on January 8th.

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