COVID-19 measures paralyzed the flu. Why experts say the next season is unpredictable

COVID-19 measures paralyzed the flu.  Why experts say the next season is unpredictable

People wear masks as they walk past a pharmacy offering flu shots in downtown Calgary on October 30, 2020.Jeff McIntosh/The Canadian Press

John Paget was stunned.

For years, the infectious disease scientist had been studying influenza B/Yamagata, one of the two main lineages of influenza B virus that sickens people around the world and dominates the annual flu season about every seven years. But in the spring of 2020, at the start of the COVID-19 pandemic, B/Yamagata infections plummeted. B.last monthAlthough other flu viruses had resurfaced, B/Yamagata had not yet, leading Dr. Paget and his colleagues to wonder if it was extinct.

“That was mind-boggling in the world of flu, for that to happen,” said Dr. Paget, a senior researcher at the Netherlands Institute for Health Services Research, noting that he and other experts still aren’t sure what to make of their flu. absence. “Has it really disappeared? Are you inactive? is waiting? To return to?

The apparent demise of B/Yamagata is just one of many unexpected effects the COVID-19 pandemic has had on the flu. And while life for many is now back to pre-pandemic normality, COVID-19 continues to exceed experts’ expectations for what was once a relatively predictable seasonal virus.

To begin with, the fact that influenza could be largely suppressed through non-pharmaceutical means, such as travel bans, restrictions on gatherings, and school closures that were widely introduced to slow the spread of COVID-19, was something that the Dr. Paget said that he and his colleagues had not done so. seen evidence of. With the exception of frequent and thorough handwashing, there was very little data before the pandemic to show that these measures could affect the flu, he said, noting that even the use of face masks against the flu was considered questionable.

However, these measures stopped the flu. According to Canada flu surveillance In the national surveillance system, sporadic positive influenza tests were reported, but no widespread community circulation of influenza occurred during the 2020-2021 influenza season, reflecting the situation globally.

When provinces and territories began lifting public health measures earlier this year, influenza also returned with an unusually late start to Canada’s flu season, which typically runs from October through March. The number of laboratory-confirmed influenza detections began growing sharply in April, at a time when they would normally be declining.

Elsewhere, the return of the flu has also not followed its usual pre-pandemic patterns. In Australiawhere flu season is typically June through September, the number of laboratory-confirmed influenza cases had surpassed the country’s five-year average by mid-April.

While flu patterns in the southern hemisphere, with earlier winter, generally foreshadow how the northern hemisphere flu season will unfold, it is not certain that Canada’s flu season this year will be similar to that of Australia.

Some suggest the large number of flu cases reported in Australia were simply a reflection of increased testing in that country, said Sameer Elsayed, an infectious disease physician and medical microbiologist at Western University. In other words, it’s possible that the flu season there wasn’t particularly worse than it was before the pandemic, it’s just that more people were being tested.

Additionally, there are multiple factors that make the upcoming flu season in Canada unpredictable. For example, COVID-19 could compete with the flu. Dr. Elsayed explained that there is something called “viral interference,” where the body, when infected with one type of virus, produces antiviral substances called interferons that fight many other types of viruses. So while it’s unknown how much of an impact viral interference might have, people are less likely to get the flu when there’s a lot of COVID-19, he said.

On the other hand, the flu can cause more symptoms, especially in young children whose immune systems have never dealt with the flu in their lives, Dr. Elsayed said.

Another potential twist is the effect of human behavior. If Canadians anticipate a bad flu season and take public health measures, such as widespread use of masks and an aggressive flu vaccination campaign, that could quell the flu again, Dr. Elsayed said. As of October 15, influenza activity was increasing in Canada, but was still at levels normally seen between seasons.

For Dr. Paget, one of the most curious observations is that even as flu activity resumed around the world, B/Yamagata has been conspicuously absent. The reason for this remains an enigma, said Dr. Paget.

But it has important implications for the formulation of future flu vaccines, he said. In Canada, influenza vaccines generally protect against three or four influenza viruses: two influenza A viruses and one or two influenza B viruses. If B/Yamagata is gone for good, policymakers Health and vaccine manufacturers will need to decide whether to omit it from the annual flu shot or replace it with another virus, he said.

In addition, it raises the possibility that if one influenza virus can be driven to extinction, others might disappear as well.

“Before COVID, no one would have thought this was possible,” Dr. Paget said.

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