Image of a woman suffering home page from flu Influenza is a disease caused by viruses of the orthomyxovirus genus, which infect the airways (nose, throat, lungs).
It is very contagious, because it is easily transmitted through droplets of mucus and saliva, with coughs and sneezes, but also simply by talking to another person, or indirectly, through contact with hands contaminated by respiratory secretions.
Influenza prevention and control
Influenza represents a serious public health problem and a significant source of direct and indirect costs for the implementation of control measures and the management of cases and complications of the disease and is among the few infectious diseases that, in fact, every man experiences several times during his life, regardless of lifestyle, age and place where he lives.
In Italy, as in the rest of Europe, the flu occurs with annual epidemics during the winter season. Sporadic cases can also occur outside the normal flu seasons, although in the summer months the incidence is negligible.
Annual epidemics: high morbidity and mortality
- Annual influenza epidemics are associated with high morbidity and mortality. Influenza strikes an average of 8% of the Italian population every year, maintaining an intermediate level compared to that observed in the 2005-2006 season,
- in which the historical minimum of influenza activity was recorded (4%), and that observed in the 2004-2005 season, in which the incidence reached the highest level (12%) since the start of surveillance in 1999.
Based on the data relating to the various influenza seasons
The epidemic curve generally reaches its peak at the beginning of February, especially affecting the pediatric population (0-4 and 5-14 years), with a cumulative incidence that decreases with increasing age (until reaching the minimum value in the over 64s).
- Severe cases and complications of the flu are, however, more frequent in people over 65 years of age and with risk conditions, such as, for example, diabetes, immune or cardiovascular and chronic respiratory diseases.
- Some studies have found an increased risk of serious illness in very young children and pregnant women. However, severe cases of flu can also occur in healthy people who do not fit into any of the categories mentioned.
The European Center for Disease Control (ECDC) estimates that, on average, around 40,000 people die prematurely each year from influenza in the European Union. 90% of deaths occur in individuals over the age of 65, especially among those with underlying chronic medical conditions. Annual circular of the Ministry
Every year the Ministry of Health prepares a circular containing indications for the prevention and control of seasonal influenza: epidemiological and virological surveillance, prevention of influenza through vaccination and personal hygiene and protection measures.
Virus mutations and pandemic risk
- The circular also indicates the categories of people for whom vaccination is recommended and offered free of charge.
- The Ministry of Health also monitors the progress of vaccinations, publishes data on vaccination coverage and promotes the national system of epidemiological and virological surveillance of influenza, InfluNet and the surveillance of serious and severe cases.
At the basis of influenza epidemiology is the marked tendency of all influenza viruses to vary, i.e. to acquire changes in surface proteins, which allow them to bypass the barrier constituted by immunity present in the population with previous experience of infection ;
This explains why the flu can repeatedly strike the population and cause recurring epidemics, the only prevention of which remains vaccination prophylaxis.
This also explains why vaccination must be repeated every year.
On the basis of laboratory data relating to circulating viruses, the World Health Organization (WHO) annually gives indications on the composition of the vaccine to be used, which is then referred to in the ministerial circular.
The influenza A and B viruses, responsible for the disease in humans
Undergo frequent and permanent changes in their genetic structure, causing the appearance of new stems from an antigenic point of view.
Antigenic changes can be:
- minor (“antigenic drift”); they are very frequent and constantly lead to the appearance of strains responsible for the flu epidemics that follow one another from year to year
of greater magnitude (“antigenic shifts”); - in fact, they occur only for type A viruses, they do not concern type B viruses and are responsible for the appearance of new subtypes of influenza viruses with very different antigenic characteristics compared to previous viruses.
“Mutated” viruses have pandemic potential, i.e. the ability to cause epidemics that spread across the entire population of the globe in a short time. The completely new characteristics compared to the circulating viruses, in fact, mean that the human population has no immunity protection (it acquires naturally or as a result of vaccination) against them.