COVID drop: Cases are declining around the world, experts say many factors are at play

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A seemingly sharp decline in global COVID-19 cases has triggered exuberance among some infectious doctors and epidemiologists, although they are unsure of the exact cause of the downward spike.

A seemingly sharp decline in global COVID-19 cases has triggered exuberance among some infectious doctors and epidemiologists, although they are unsure of the exact cause of the downward spike.
Tables and charts illustrating the burden of COVID in most countries, including Canada and the United States, show steep dives from all-time highs just a few weeks ago.

Experts say a combination of factors are likely at play in the virus’s apparent decline, including a seasonal aspect of SARS-CoV-2, some level of herd immunity in some locations, and the impact of lockdowns and lockdowns. our own behaviors.

The fact that the drop is happening now, amid the threat of more transmissible variants, seems a bit puzzling, however, says Winnipeg epidemiologist Cynthia Carr.

“That’s the really interesting part about it,” she says. “We know these variants have spread much faster and we’ve seen them become more dominant, but the numbers are still not exceeding how we might have predicted.

Carr says the worrisome variants – those first detected in the UK, South Africa and Brazil – have been found in several countries and are quickly overtaking older strains in some places. In Berlin, for example, she notes that the variant first detected in the UK accounts for 20% of new cases, up from 6% two weeks ago.

Carr suspects that one of the reasons for the lack of an increase in cases could be because governments have gotten better at setting public health directions over the past year and people have become better off. managed to join it.

But as things appear to be improving, Carr warns that “we can’t rest on our laurels now.”

“Once (the variants) make up 90, 100 percent of all infections… we could really see this escalation,” she said.

Infectious disease specialist Dr. Sumon Chakrabarti in Mississauga, Ont., Agrees people shouldn’t assume the pandemic is over because cases around the world are declining. But the global decline is a positive development that should not be overlooked, he added.

Chakrabarti says there are probably several reasons for this decline, with the situation in some countries being explained more easily than others.

Vaccination efforts could be credited in Israel, for example, where 87% of the population has received at least one dose of a COVID vaccine. Countries like Canada, which have been mostly on lockdown in the past six weeks, may point to restrictions and limited contact as a plausible reason for their decline in COVID.

More than one factor could also work in different regions, Chakrabarti added. And a possible seasonal aspect of the COVID virus can be an overarching theme.

Infections caused by some viruses tend to peak once a season before easing naturally, Chakrabarti says, like the flu, which typically peaks between November and January. Other coronaviruses have followed a similar pattern.

“Seasonality means that (viruses) are cycled at some point in the season,” he said. “We don’t know if that’s 100% the case with COVID. But it could be. ”

While the timing of the first wave of COVID in Canada last spring seems to run counter to the notion of seasonality, we weren’t exposed to large amounts of the virus until March, so it didn’t have the chance to travel earlier, explains Chakrabarti.

Some parts of the world, including the United States, may also face some level of herd immunity brought on by natural infection, Chakrabarti says, which could simplify, but not entirely, their recent drop in cases.

Although the exact number of COVID infections is difficult to assess, Chakrabarti estimates that undetected cases could be five to 10 times higher than reported cases, either because people were truly asymptomatic or had symptoms so minor that ‘they have never been tested.

“If you have a significant number of people who have been infected and have, maybe not necessarily full immunity, but some degree of immunity, at the very least that should slow the outbreaks,” Chakrabarti said.

However, the concept of collective immunity poses problems.

University of Toronto epidemiologist Dr Prabhat Jha says that although experts believe people who have had COVID infections in the past may have some protection against the variants first detected in the UK and South Africa, which may not be the case with that found for the first time in Brazil.

Jha points out that not all countries are seeing a decrease in COVID cases – Brazil is a region with stable rates or possible increases – and he fears the labeling of herd immunity as the reason for the drop in cases. could be dangerous.

“We don’t know what collective immunity really means,” he said. “It’s a theory that in a number of people who are infected, the virus is running out of customers. But we have very little basis to understand what this level is.

Jha says the potential reasons for the global decline are only theoretical at this time.

“No one really has a clear idea of ​​why cases are down,” he said. “So I think you have to be very careful when you talk about plausible explanations. ”

This report by The Canadian Press was first published on February 23, 2021.

Melissa Couto Zuber, The Canadian Press

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