Friday, December 09, 2022

Why the Twin Pandemic of Corona Virus and Flu Could Never Happen – 04/13/2022 – Balance & Health – Play Crazy Games

An intriguing theory may help explain why the flu and COVID-19 didn’t dominate the United States at the same time – the so-called twin pandemic that many public health experts feared.

The idea is that it was not just masks, social distancing or other restrictions from the pandemic that caused the flu and other respiratory viruses to disappear as the coronavirus reigned and re-emerged.

Exposure to respiratory viruses can put the body’s immune defenses on high alert, preventing other invaders from entering the airways. This biological phenomenon, called viral interference, limits the amount of respiratory virus that can circulate in an area at any one time.

“My hunch, based on my recent research, and my feeling is that viral intervention is real,” said Ellen Foxman, an immunologist at Yale School of Medicine. “I don’t think we’re going to have flu and coronavirus spikes at the same time.”

On an individual level, she said, some people may be infected with two or three viruses at the same time. But at the population level, according to this theory, one virus outperforms another.
Still, she cautioned: “The health care system may be overwhelmed well before the upper limit of circulation is reached, as O’Microon’s wave showed.”

Viral interference may help explain patterns of infection observed in large populations, including those that may arise when the coronavirus becomes endemic. But the research is in its infancy, and scientists are still struggling to understand how it works.

Before the coronavirus became a global threat, the flu was one of the most common serious respiratory infections each year. In the 2018-2019 season, for example, it was responsible for 13 million medical consultations, 380,000 hospitalizations and 28,000 deaths.

The 2019-2020 flu season was coming to an end before the coronavirus spread around the world, so it was unclear how the two viruses might affect each other. Many experts feared that a twin pandemic, the virus would hit crowded hospitals the following year.

These concerns have not been realized. According to the Centers for Disease Control and Prevention (CDC), cases remained exceptionally low during the 2020-2021 season as the coronavirus continued to spread, despite a weak effort to increase flu vaccination. ,

Only 0.2% of samples tested positive for the flu from September to May, compared with about 30% in recent seasons, and flu hospitalizations were the lowest on record since the CDC began collecting this data in 2005. .

Many experts attributed the flu-free season to masks, social distancing and restrictions on movement – especially for young children and older adults, both of whom are at increased risk of getting severe flu. A year later, flu numbers peaked in the winter of 2021-2022, when several US states waived restrictions, but numbers were still below pre-pandemic averages.

So far this year, the US has recorded nearly 5 million cases, 2 million doctor visits, less than 65,000 hospitalizations and 5,800 flu-related deaths.

Instead, the coronavirus continued to dominate the winter, far more common than the influenza virus, respiratory syncytial virus, rhinovirus, and the common cold virus.

Respiratory syncytial virus, or RSV, typically emerges in September (fall) in the Northern Hemisphere and peaks in late December to February (winter), but epidemics have distorted their seasonal patterns. It remained low throughout 2020 and peaked in the summer of 2021 when the coronavirus hit its lowest level since the start of the pandemic.

The idea of ​​some sort of interaction between viruses emerged in the 1960s, when polio vaccines, which contain weakened polioviruses, significantly reduced the number of respiratory infections. The idea gained ground in 2009: Europe seemed set for a spike in swine flu cases later that summer, but when schools reopened the rhinovirus winter somehow seemed to stop the flu pandemic.

“This led many people to speculate about the idea of ​​viral intervention at the time,” Foxman said. Even in a normal year, rhinovirus peak occurs in October or November and again in March at the end of flu season.

Last year, a team of researchers began studying the role of existing immune responses in fighting the flu virus. Since intentionally infecting children with the flu would be unethical, he gave children in The Gambia (West Africa) a vaccine with a weakened strain of the virus.

Virus infection triggers a complex cascade of immune responses, but the first defense comes from a set of non-specific defenders called interferons. The team found that children who already had high levels of interferon had far fewer flu viruses in their bodies than those with low levels of interferon. The findings suggested that previous viral infections prompted the children’s immune systems to fight off the flu virus.

Tushan de Silva, an infectious disease specialist at the University of Sheffield in England, who led the study, said, “Most of the viruses we have seen before vaccination in these children were rhinoviruses.”

This dynamic may partly explain why children who have more respiratory infections than adults are less likely to be infected with the coronavirus. The flu can also prevent coronavirus infection in adults, said Guy Boivin, a virus and infectious disease specialist at Laval University in Canada.

Recent studies have shown that flu and coronavirus co-infections are rare, and people with an active influenza infection are about 60% less likely to test positive for the coronavirus, Boivin said.

“We are now seeing an increase in flu activity in Europe and North America, and it will be interesting to see if the Sars-CoV-2 circulation decreases in the coming weeks,” he said.

Technological advances in the last decade have made it possible to show the biological basis of this intervention. Foxman’s team used a tissue model of the human airway to show that rhinovirus infection stimulates interferons that can ward off the coronavirus.

“The protection is for a certain period of time while you have the interferon response triggered by the rhinovirus,” said Dr Pablo Murcia, a virus specialist at the MRC Center for Virus Research at the University of Glasgow, whose team found similar results.

But Marcia also discovered a twist in viral interference theory: The onslaught of the coronavirus could not prevent infection by other viruses. He said it may have something to do with the ability of the coronavirus to evade the immune system’s initial defense.

“Compared to the flu, it activates these antiviral interferons less,” Silva said of the coronavirus. This finding suggests that, in a given population, it may be important which virus appears first.

Silva and his colleagues collected additional data from The Gambia – with no epidemiological restrictions that could have influenced the observed viral patterns – showing that rhinovirus, flu and The coronavirus was at its peak.

That data “convinced me a little more that intervention might play a role,” he said.

Nevertheless, the behavior of viruses can be greatly influenced by their rapid evolution and by social restrictions and vaccination patterns. Therefore, the potential impact of viral intervention is unlikely to become apparent until the coronavirus settles in a predictable endemic pattern, experts said.

RSV, rhinovirus and flu have coexisted for years, said Nassia Safdar, a specialist in healthcare-related infections at the University of Wisconsin-Madison.

Safdar said of the coronavirus, “Over time, the same thing will happen to him, he will become one of many.” Some viruses may outweigh the effects of others, she said, but the patterns may not be immediately apparent.

Looking at the common cold, some researchers have predicted that Sars-CoV-2 will become a seasonal cold infection that may coincide with the flu. But the coronavirus that causes Kovid-19 has already shown itself to be different from its cousins.

For example, it is rarely seen in co-infection, while 1 in 4 common cold coronaviruses is often seen as co-infection with the other three.

“It’s an interesting example that makes us hesitate to make generalizations about many viruses,” said Jeffrey Townsend, a biostatistician at the Yale School of Public Health who has studied the coronavirus and its seasonality. “It seems a little virus-specific how these things happen.”

Translated by Luiz Roberto M. Gonsalves

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