The flu season is coming to an end, also thanks to the climate. This is demonstrated by the numbers reported by the RespiVirNet surveillance system of the Istituto Superiore di Sanità. In Easter week, over 300,000 Italians were put to bed by flu-like syndromes, even if they were 25 thousand less than the previous week. The numbers, however, say that it was children who paid the price of the most classic virus of the winter season and the beginning of spring, with 15.30 cases per thousand.
While we are taking stock of what happened, we are already thinking about the future. And they propose the strains that will be contained in the vaccines which will be marketed next autumn. The World Health Organization (WHO) makes the “forecasts”, based on data from the Global Sentinel Flu Surveillance Network.
It is essential to begin the development of vaccines
WHO therefore established the vaccination composition for next autumn. And in September it will do the same thing for the southern hemisphere in order to continue updating the vaccine so that it is as close as possible to the circulating viruses.
“This anticipation is necessary because from this moment manufacturing companies will be able to begin developing influenza vaccines to market starting from autumn 2024 and which every year require a re-evaluation from the point of view of safety and effectiveness, even if they are now consolidated technologies – explains Fabrizio Pregliasco, Scientific Director of Osservatorio Influenza, Director of the specialization school in hygiene and preventive medicine of the University of Milan and company healthcare director of the IRCCS Galeazzi Sant'Ambrogio hospital in Milan”.
A tailor-made vaccine
Obviously not all vaccines are the same. It is essential to think about preparations suitable for different ages of life and above all with specific characteristics based on the type of subject to whom they are administered, both by age and by general state of health and frailty. In this way the aim is to maximize its effectiveness also according to the characteristics of the subject, an effectiveness which certainly manages to avoid the heaviest effects of the disease such as the risk of death although, as is well known, we cannot speak of an effectiveness of the 100%. This is also affected by the fact that sometimes, when we talk generically about the flu, we also take into account symptoms linked to a cocktail of viruses. The vaccine protects only against influenza viruses.
As part of the vaccination composition this year, among other things, they are expected only 3 viral strains: 2 type A (one AH1N1 and one AH3N2 updated this year with a Thai variant) and 1 type B (B/Victoria which however has not been updated). The EMA has in fact suggested “lighten” the wording no longer including the B/Yamagata strain as this strain has no longer been in circulation since March 2020 and therefore no longer appears to represent a threat to public health.
“We therefore expect a season from a virological point of view not particularly heavy as was the case last year precisely because viruses have not changed particularly and therefore a significant share of people who contracted the flu virus last year will be able to enjoy some sort of protection – Pregliasco says. Nonetheless, we will still have to see how the virus evolves because, like every year, it is not only the composition of the virus that determines the number of flu cases but also meteorological and environmental conditions; it is therefore always important not to underestimate the vaccination booster, particularly for those at risk and those who are advanced in age.”
What is the flu
It is a viral disease. It mainly affects the respiratory tract, giving rise to fevereven higher than 38 degrees, widespread weakness, headache, cough and phlegm. Complications are rare, but should not be underestimated. In particular when, due to the weakening of the body's defense system, they develop bacteria that they can give severe bronchitis or pneumonia.
It is caused by a virus formed by a central body that contains the genetic heritage wrapped in a covering composed of two proteins fundamental for its diffusion in the human organism. Hemaglutinin guides the virus and allows it to enter the cells, selecting those of the respiratory system. Neuraminidase, on the other hand, acts like a chisel from the inside and allows the new viruses formed inside the cell to exit and infect other cells.
How the flu spreads and how it is treated
The virus is transmitted through droplets emitted from the respiratory tract of those who have contracted the infection or through contaminated objects (for example handkerchiefs). Even hands, if not carefully washed, can become an important transmission vehicle. The risk of transmission is very high because the disease has an incubation period of 1-3 days during which, even without experiencing any discomfort, one is extremely contagious. Infection is highest in the 24 hours before the onset of fever. As regards therapy, it must be remembered that normal flu is a self-limiting disease, that is, it tends to pass on its own. For this reason, rest in the heat and a light diet rich in liquids help limit the damage. A normal antipyretic can be taken against fever.
How flu viruses are made
These are strains that are part of the family Orthomyxoviridaetype orthomyxovirus. They have the shape of a sphere, more or less similar to a football although of infinitesimal dimensions compared to it, we are in the order of 80-120 nanometers in diameter. But above all on their external surface they appear “thorny”, because they have some thin protuberances called in scientific terms “spikes”.
These structures are fundamental for the body's response to the virus, for the activity of drugs and for the development of vaccines. On these protuberances are in fact the so-called surface antigens, i.e. hemagglutinins (marked by the acronym H) and neuraminidases (marked by the letter N). These two elements are fundamental for the definition of virus subtype: in fact, for each influenza strain, a letter is used which characterizes the viral “family” in general terms based on the internal antigens (A, B and C); for type A, the two acronyms H and N, followed by a number specifically distinguish the antigens of the single strain. However, there is no subtype for viruses B and C. Obviously the complex structure of the virus is not limited to its external part. In fact, the viral genetic heritage is present inside it, in the form of ribonucleic acid (RNA). Type B and C viruses have humans as their only reservoir, while those of type A can infect various animal species: for example pigs, horses, birds and poultry as well as ducks. Indeed, these viruses can also infect marine mammals, such as dolphins or whales.
