Gone, but promised to return: what to expect from the influenza virus that disappeared during the COVID-19 pandemic

Extraordinary personal protective measures taken around the world in connection with the coronavirus pandemic have led to a sharp decrease in the incidence of common types of influenza, and two subtypes of viruses, according to experts, could have disappeared altogether. Air force.

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To explain the mechanism of the disappearance of viruses, one should understand their classification.

Seasonal flu epidemics are caused by two families of viruses: influenza A and B.

Influenza A viruses are divided into subtypes based on two proteins on their surface - hemagglutinin (H) and neuraminidase (N).

Now the H1N1 and H3N2 viruses circulate among the population, each of which is subdivided into the so-called clades.

In turn, influenza B viruses are not divided into subspecies or clades, but have two lines (pedigrees, if you will) - B-Yamagata and B-Victoria.

So, the H3N2 hoard, known as 3c3.A, and the B-Yamagata line have not been registered since March 2020.

On the subject: During the COVID-19 pandemic, the flu disappeared in the world: its return could be a disaster

Unlike the biological diversity of species in nature, the reduction of species or diversification in viruses is a good sign (for humanity).

Every year, vaccine developers, several months before the flu season, track the strains circulating around the world and try to guess which ones will be the most common (after all, it is not possible to vaccinate against all types of flu - it is too difficult and expensive ).

So the fewer strains there are, the easier it is to make a choice and the more likely you are to get the right vaccine.

The H3N2 group is especially diverse, and before the pandemic, the clades of this virus multiplied every year.

“In the past, when we made vaccine recommendations, this virus was always a headache,” says WHO spokesman Richard Webby. So, he said, the dramatic decline in diversity of this virus was great news.

However, Webby advises not to flatter yourself ahead of time, since the fact that the virus has not been mentioned in official statistics for a long time does not mean that it has disappeared completely.

The upcoming flu season can be tough

One child in the United States has died from the flu this year. In 2019-2020, 199 children died from the virus, up from 144 in the previous season. Flu cases, which usually number in the tens of millions, amounted to only a few thousand in the United States this year, notes ABC7.

“There was no flu anywhere except for some reasonable activity in West Africa,” Webby said.

“Nobody saw him. This includes countries that have imposed a lockdown. Countries that did not apply any restrictions. Countries that handled the pandemic well. Countries that have not done a good job,” the expert said.

It's not entirely clear why. Many experts believe that the measures taken to combat the coronavirus have also prevented the spread of the flu. It is also possible that the coronavirus has somehow defeated or prevented the flu. In any event, Webby and other experts believe the interruption in flu activity is temporary. They fear that the flu will return, probably this fall, with a vengeance.

“We may be heading into the worst flu season we've ever had,” Webby said.

“When it comes back, it's going to be a challenging season,” agreed Aubrey Gordon, an epidemiologist who studies influenza at the University of Michigan School of Public Health.

One of the reasons the upcoming flu season is likely to be bad can be attributed to human behavior. People tired of isolation, wearing masks and keeping their distance will want to celebrate the freedom offered by vaccines that protect them from the coronavirus and mitigate the pandemic. And they can overdo it.

Travel is already increasing, restaurants are filling up again, and schools are planning to reopen with face-to-face classes.

But while people flocking to resorts, bars, and family gatherings may stay protected from the coronavirus, it will not protect them from the flu or other respiratory viruses that spread in the same way as the coronavirus: in the air, in droplets and on surfaces.

“I think with more people not wearing masks and less social distancing, there will be an uptick in common respiratory infections that we see seasonally,” says Allison Aiello of the University of North Carolina School of Public Health.

Aiello says North Carolina is already seeing an increase in respiratory diseases.

“We should expect some increase, especially in the fall when kids go back to school,” she said.

It's not just the flu to be afraid

“It's not just the flu. These are all other respiratory viruses,” Webby said. These include not only influenza, but also respiratory syncytial virus or RSV, adenoviruses, strains of coronavirus that cause colds, rhinoviruses and others.

"As we take Covid mitigation measures and children return to school in person and we all begin to travel again, especially internationally, there will be many more opportunities for all types of respiratory viruses to become infected and spread," she said. Lynette Brammer, who leads the influenza surveillance team at the US Centers for Disease Control and Prevention.

“And we certainly expect influenza and all the other respiratory viruses that have been at low levels over the last year to return,” she added.

However, Brammer is cautious about his projections.

“Flu is always unpredictable, and that’s truer now than ever,” she said.

There is a second reason to believe that the 2021–2022 flu season might be bad. There is an undocumented theory that the human body's immune response is naturally enhanced by repeated annual exposure to viruses such as the flu. These influences may not be enough to make people sick, but they are enough to remind the immune system to maintain its defenses.

“The longer you are not exposed to the flu, the more likely you are to develop symptoms and the more likely you are to get sick,” Gordon said. - The more symptoms you will have. This leads to more severe cases. We know that for sure."

The same goes for RSV, coronaviruses other than Covid-19, and other infections.

“I would actually worry about all of them. All of them can cause serious illness. All of them can cause pneumonia,” Gordon added.

RSV affects infants and very young children in particular. It kills between 100 and 500 children and 14 adults annually, mostly over the age of 000. Many of the 65 million babies born during the pandemic will become infected with RSV and other viruses for the first time when they first go to kindergarten.

“We don't know what the consequences of all these young children delaying their first exposure to RSV will be,” Gordon said. “There will likely be very large epidemics of RSV.”

Aiello is less confident about the possible effect of avoiding germs for a year or so. A few years of avoiding exposure will have an impact, she believes, but 15 months or so while people distancing themselves from society, working from home or not going to school may not be enough to affect the immune system.

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Each season is unique

But the fall respiratory flu season can be tough anyway, Aiello says. At least many children will be exposed to a variety of viruses in one season, when they should have been exposed to them within 2 years.

“When you haven't been sick for a while, it may seem like you have more severe symptoms,” she said.

Influenza will be the only virus that can be measured. Doctors don't test people for most other respiratory viruses—largely because there is no specific treatment for them—but the U.S. Centers for Disease Control and Prevention (CDC) tracks the flu. According to them, the virus kills between 12 and 000 people a year, depending on the season.

The 2019-2020 season was mild, with 38 million people in the U.S. getting the flu, 18 million seeing a doctor, 400 sick enough to be hospitalized, and 000 dead. According to the CDC, about 22% of the US population gets the flu every season, with a range of 000% to 8%, depending on the season.

Much will depend on how many Americans get vaccinated. Just under half of the population gets the flu vaccine every year, although the CDC recommends getting an annual vaccine for almost everyone over the age of 6 months.

One thing the CDC knows for sure: flu activity is impossible to predict.

Brammer says she has watched each flu season for decades and each is unique.

“Every time you think you know what’s going to happen, it’s going to be completely different,” she said.

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