Flurone: what is the double infection of influenza and covid viruses and why is it not so rare

In recent days we have witnessed an expected and worrying event according to the media: the coexistence in a person of two viruses at the same time, the flu and SARS-CoV-2.

So much so that we already have a name for the new infection, flurone, which is searching and capturing. Please do not confuse it with a heterocyclic chemical of the same name related to fluorescent and pharmacological compounds, because it has nothing to do with it.

After two years of a pandemic, it was as if we waited for this to happen and confirmation had to come from abroad. Of Israel specifically, although it seems that it had already happened before even in Spain.

Although now it seems that it is a danger, possibly the lion is not as fierce as it is painted.

Before activating the alarms, we must ask ourselves if this fact is truly important or just one more phenomenon that occurs and occurred long before the pandemic with a greater frequency than we think.

We may once again have too much noise for so few nuts.

Respiratory viruses everywhere

More than two hundred viruses cause respiratory diseases in humans. They are not few.

Of them, most produce very similar symptoms such as sinusitis, pharyngitis, laryngitis, tracheitis, bronchitis, etc, etc … That is, infections of the respiratory tract that cause inflammation.

Regarding local inflammation, it only represents the activation of the immune system against viral infection, regardless of the virus.

A few years ago a study was carried out on viruses that live with us and that are located in the lungs and they were found up to 19 different types.

These viruses are the roundviruses (you can imagine why they are called that) and they do not cause disease unless our immune system is somewhat damaged.

The relationship between virus and disease is relatively complex since everything depends on the severity of the symptoms they produce.

In many cases, the symptoms are so mild that we do not even appreciate them since the relationship between the virus and the immune system does not produce aggressive responses.

In other cases, viruses are even useful to prevent other diseases such as bacterial infections, since the cells they infect are not ours but bacteria and thus they control the population of bacteria that could cause us diseases.

You know, “the enemy of my enemy is my friend.”

The relationship between microorganisms and the immune system it is established since we are born.

We are subjected to invasion by multiple microscopic bacterial or viral organisms from birth and our survival is determined by our body’s ability to keep them at bay.

People with immunodeficiency know very well that not having an efficient immune system makes them a target of even the most innocuous microorganisms.

There we have the example of HIV patients and the recurrent and deadly diseases they suffered before the antivirals arrived.

Flu viruses and coronaviruses are not the same

Since the beginning of the pandemic, there has been some suspicion of the coexistence between the flu wave and the coronavirus wave.

It is not because they are two similar viruses, which they are not, but because both can cause saturation of the health system separately, as they have already shown.

Influenza viruses belong to the large family of orthomyxoviruses. In this family we have influenza viruses A, B, C and D.

Of them, A and B cause the seasonal epidemic that visits us year after year (except last year thanks to social isolation measures).

Specifically, influenza A are those that cause pandemics, while B have less travel, C create mild diseases and are not considered pandemic and D essentially affect livestock.

Flu viruses contain two important proteins in their membrane that characterize them.

It is hemagglutinin (H), which serves to infect cells by binding to a membrane sugar -sialic acid- and neuraminidase (N), which are used by the new virions to separate from sialic acid and be able to infect a new cell.

In humans, 18 types of hemagglutinin and 11 types of neuraminidase have been characterized and their combination determines the type of virus that affects us year after year.

Some combinations have been shown to be very lethal, such as H5N1, but they have not shown the ability to spread easily among humans, for now.

Coronaviruses, however, use another well-known mechanism. Its Spike (S) protein binds to the ACE2 protein of the respiratory epithelium (including the lung) and thus infects the cells of the respiratory tract.

Another big difference between flu viruses and coronaviruses is their genome.. While in influenza viruses the genome is made up of 8 pieces of negative RNA, that of coronaviruses is made up of a single strand of positive RNA.

This assumes that the respective genome replication mechanism is very different.

In addition, in the remote assumption that both viruses infect the same cell, it is impossible for combinations of their genomes to be produced that can give rise to a viable virus with hybrid characteristics.

The possibility, if it existed, would be extremely remote and would be a true molecular surprise.

The real risk is in the symptoms it generates

The danger of co-infection with two aggressive respiratory viruses such as SARS-CoV-2 and an influenza virus in unison would be found in the response to the infection, that is, in the symptoms.

Seasonal flu is capable of causing thousands of deaths annually by itself even in vaccinated people, since their immune systems cannot stop the infection.

Therefore, if both viruses co-infect an immunologically depressed person, their combined action would generate known symptoms such as pneumonia, cytokine storm and multi-organ failure that also occur in cases of influenza, respiratory syncytial virus, pneumococci and others respiratory pathogens separately.

Apart from this problem, which is already worrying in itself, the other speculations about the recently christened disease with such an unattractive name should be considered nothing more than speculations lacking a solid scientific basis.

In any case, it should already be clear that to be prevented against influenza and SARS-CoV-2 infection, the best strategy is boosting the immune system with vaccination.

* This article was originally published on The Conversation. You can read the original version here.

Guillermo López Lluch is a professor in the area of ​​Cell Biology, an associate researcher at the Andalusian Center for Developmental Biology and a researcher in metabolism, aging and immune and antioxidant systems at the Pablo de Olavideen University in Seville.

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