what do we risk in case of human-to-human contagion

Less than a week after the news of the third human case of avian influenza A (H5N1) in the United States, today, June 6, 2024, theWorld Health Organization (WHO) announced that a man in Mexico died after contracting the A H5N2 virus. It is a different strain from what is circulating in the cow farms in the United States, but remains – explained the WHO – the “first human case confirmed in the laboratory of influenza A (H5N2) virus infection reported globally”.

Although the man had other underlying conditions – it is therefore impossible to establish with certainty whether his death was caused by avian influenza or not – the fact that has not had contact with poultry farms (where the virus has been detected), nor with other animals is a non-negligible fact. Even if we are talking about two different strains of avian influenza, it is clear that this news has increased the alarm levels on the risks of a possible large-scale contagion among men.

Specifically, special observation is the H5N1 viruswhich in recent months has made the leap from birds to species, infecting many other mammals, most recently in dairy cows on several farms in the United States, where the three cases of human infection also come from. As the European health authorities have also underlined, the fear now is that this virus you continue to change until it adapts to man. But how realistic is it the risk of a new pandemic? Fanpage.it asked the Prof. Giovanni Rezzaprofessor of Hygiene at the Vita-Salute San Raffaele University of Milan and former general director of Health Prevention of the Ministry of Health during the Covid-19 pandemic.

What changes with the first case of death from avian flu in Mexico?

In reality, this news adds nothing to the information on the pandemic risk linked to the highly pathogenic avian influenza A (H5N1) virus (HPAI) because the person who died in Mexico had contracted a different subtype of the same virus, H5N2, different from ‘H5N1, which is the strain that is circulating in livestock in the United States.

However, this does not mean that the news should be underestimated. In fact, it reminds us that various viruses are circulating in the animal world that could make the so-called species leap, passing from animals to humans. In fact, there are several avian viruses that could mutate and adapt to humans. It is not certain that they will do so, but this possibility exists. For this reason, the case in Mexico leaves questions unanswered.

What questions are you referring to?

The aspect that leaves us somewhat concerned about this specific case is the absence of information on the methods of contagion. Let me explain better: we don’t know how the person contracted the virus, if he was infected by birds or if the virus passed from person to person. We cannot know, but this would change the cards on the table, because in the case of human-to-human contagion we would be faced with confirmation of the fact that that virus can also transmit from human to human.

Let’s go back to the avian influenza A (H5N1) virus. The cases in the United States are creating some fear. Is there a pandemic risk or not?

The risk of a pandemic is always there. An influenza pandemic is a phenomenon that can never be ruled out, but at the same time it is not predictable: we cannot know that there will be a pandemic until it occurs.

So why do we talk so often about avian risk in humans?

With respect to H5N1, there has been talk of a risk of a new pandemic because we are faced with a virus that has caused around 900 human cases since it began circulating at the beginning of 2023. This data has caused some concern and the virus is now a special observation. But let’s not forget that there are many other animal viruses, avian but also porcine, which are capable of making the leap from animal to human. As the case of the man in Mexico demonstrated. However, without causing alarmism, even when this occurs it is not certain that the virus will mutate and adapt to humans to the point of becoming transmissible from person to person. This is the real danger.

To understand better: are the several deaths among cows on US farms proof that the virus has adapted to a new species?

In reality, from what has been observed in the laboratory, the virus found in dead cows does not show such a high number of mutations. The fact that it managed to infect several specimens may also depend on the presence of some receptors different from human ones and which could make it circulate in some animal species more than what happens among humans.

Do we know what could happen if the virus adapted to humans? So far human cases of H5N1 have not caused serious symptoms…

It’s very difficult to say. In the event that a more efficient passage from person to person occurred, therefore a consequence of a mutation of the virus that made it able to adapt to humans, it is not certain that the virulence would remain the same, we do not even know what symptoms it could cause in the event of infection, it is not certain that they will remain the same as those we see today in individual cases of human infection.

What about Italy? Is our situation less at risk?

So, without prejudice to the limits that we have said so far regarding the impossibility of predicting a new human pandemic, we can say that the risk of contagion discussed in the United States with respect to the consumption of raw milk in Italy does not exist because the H5N1 virus does not it is circulating in our cows and even if it were to be found in our farms, in Italy the milk on the market is only pasteurized, so we would not be exposed to this risk. In short, this seems to me to be the least of the problems.

What can we do today to protect ourselves?

We need to keep our attention on these viruses and improve surveillance systems. We have vaccines that could easily be adapted to be administered on a large scale, but it would still take 4-6 months to do so. At this moment we should not be alarmed, but we must also prepare for worse scenarios.