In recent days we have witnessed an expected and worrying event, according to the media. It is about the coexistence in a person of 2 viruses at the same time; that of the flu and SARS-CoV-2. We even have a name for the new infection; the flurona, which goes in search and capture.
But, please, do not confuse it with a heterocyclic chemical compound of the same name related to fluorescent compounds and for pharmacological use, because it has nothing to do with it.
A lot of information to read about
After 2 years of the pandemic, it was as if we were waiting for this to happen and confirmation had to come from abroad. From Israel specifically, although it seems that it had already happened before, even in Spain. Although now it seems that it is quite a danger, the lion may not be as fierce as it is painted.
Before activating the alarms we must ask ourselves if this fact is really important. Or is it just one more phenomenon that occurs and was occurring long before the pandemic with a greater frequency than we think. We may once again have too much noise for too few nuts.
Respiratory viruses everywhere
More than 2 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… That is, they are respiratory tract infections that cause inflammation. As for local inflammation, it only represents the activation of the immune system against viral infection, regardless of the virus it is.
A few years ago, a study was carried out on viruses that live with us and that are located in the lungs and up to 19 different types were found. These viruses are the round viruses (you can already 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. This is because everything depends on the severity of the symptoms they produce. In many cases, the symptoms are so mild that we do not even notice them since the relationship between the virus and the immune system does not produce aggressive responses.
Woman lying down with flu symptoms
The danger of co-infection with 2 aggressive respiratory viruses such as SARS-CoV-2 and a flu virus would be found in the symptoms.
In other cases, even viruses are useful in preventing other diseases such as bacterial infections. This is because the cells they infect are not ours but those of bacteria and thus control the population of bacteria that could cause us diseases. You know, that “the enemy of my enemy is my friend”.
The relationship between microorganisms and the immune system is established from birth. We are subject 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 suffering from immunodeficiency know very well that not having an efficient immune system makes them a target for even the most innocuous microorganism. There we have the example of HIV patients and the recurrent and fatal diseases they suffered before antivirals arrived.
Influenza viruses and coronaviruses are not the same
Since the start of the pandemic, there has been some suspicion of the coexistence between the wave of flu and the wave of coronavirus. It is not because they are 2 similar viruses, which they are not. If not because both can produce saturation of the health system separately, as they have already shown. Influenza viruses belong to the large family of orthomyxoviruses. In this family, we find influenzaviruses A, B, C, and D.
Illustration of the H3N2 influenza virus
The hemagglutinin (orange) and neuraminidase (green) proteins can be seen in this illustration of the H3N2 influenza virus.
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 viruses are the ones that cause pandemics while B viruses have less travel. The C viruses create mild illnesses that are not considered pandemics, and the D viruses essentially affect cattle.
Influenza viruses contain 2 important proteins in their membrane that characterize them. These are hemagglutinin (H), which is used to infect cells by binding to a membrane sugar -sialic acid- and neuraminidase (N), which is used by new virions to separate from sialic acid and be able to infect a host. 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.
Illustration of the Spike (S) protein of the SARS‑CoV‑2 virus binding to an ACE2 receptor.
Some combinations have been shown to be very lethal, such as H5N1, but have not yet shown the ability to spread easily among humans. Coronaviruses, however, use another mechanism that is already known. Their Spike (S) protein binds to the ACE2 protein of the respiratory epithelium (including the lung) and thus infects the cells of the respiratory tract.
Influenza virus and coronavirus
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 means that the respective mechanism of genome replication is very different.
In addition to that, in the remote assumption that both viruses infect the same cell, it is impossible for their genomes to be combined that could give rise to a viable virus with hybrid characteristics. The possibility, if it existed, would be extremely remote and would be a real molecular surprise.
The real risk is in the symptoms it generates
The danger of co-infection with 2 aggressive respiratory viruses such as SARS-CoV-2 and a flu virus in unison would be found in the response to infection, that is, in the symptoms. Seasonal flu is capable of producing thousands of deaths per year by itself. This even in vaccinated people, as their immune systems cannot fight off the infection.
Therefore, if both viruses co-infect an immunologically depressed person, their combined action would generate symptoms already known as pneumonia; the cytokine storm and multiorgan failure thatalso occur in cases of influenza, respiratory syncytial virus, pneumococcus, and other respiratory pathogens separately.
Young girl being vaccinated
The best prevention against flu and Covid-19 is to strengthen the immune system with vaccination.
Apart from this problem, which is already worrying in itself, the other speculations about the recently baptized disease with such an unattractive name should be considered nothing more than speculation lacking a solid scientific basis. In any case, it should already be clear that to be prevented against the flu and SARS-CoV-2 infection, the best strategy is to strengthen the immune system with vaccination.