In recent days we are starting to record, still sporadically, the first cases of seasonal flu in Italy for 2024. The 2024/2025 vaccination campaign began in October and will continue for the duration of the flu season. This year, 8 types of vaccines have been authorized, each suitable for certain categories of people. With autumn and the first cold weather we begin to talk about influenza and the administration of flu vaccines. It is one of the few viral diseases to which one does not develop immunization after being infected for the first time, but one can also get sick every year and this is due to the extreme genetic variability of the different strains of influenza viruses. Often underestimated compared to other infections, the flu is actually estimated to cause worldwide from 290,000 to 650,000 deaths per year for respiratory consequences; Alone in Europe, between 10% and 30% of the population becomes infected every year. Influenza is dangerous for vulnerable subjects such as children, the elderly or at-risk categories, but it can cause serious complications such as pneumonia, encephalitis and myocarditis even in healthy adults. Prevention is carried out precisely through the vaccine. In Italy all flu vaccines are authorized by AIFA (Italian Medicines Agency) and EMA (European Medicines Agency).
A premise: influenza viruses, what they are and types
The influenza viruses that circulate throughout the world and which in our latitudes present epidemic peaks during the winter are respiratory viruses because they affect the upper (nose and throat) or lower (bronchi and lungs) airways and are transmitted by inhalation of infectious respiratory droplets from one individual to another. The incubation period is usually 2 days, but can vary from 1 to 4 days. They belong to the Orthomixoviridae family and, since the first influenza virus was isolated in humans in 1933, four types have been classified: the type A virus and the type B virus, mainly responsible for flu symptoms, the C type almost always asymptomatic e the D type for which the mechanism of infection is not yet clear.
In this season, mainly type A viruses and a small amount of type B are circulating in Italy. The A strains are coded by convention with the letters H and N (for example H1N1, H3N2) corresponding to the initials of two proteins that characterize the surface of these pathogens, thehaemagglutinin (HA) and the neuraminidase (NA). Influenza virus strains have the characteristic of undergoing continuous variations over time and for this reason vaccines must be updated and reformulated every year. Based on what has already been observed in recent months in the southern hemisphere where the seasonal flu has already passed, the symptoms that can be expected from this flu wave appear to be rather severe.
What is the flu vaccine, when can it be done and its composition
In February of each year, theWHO (World Health Organization) provides information on the correct composition of influenza vaccines for the following season (for example, the vaccine formulation for the 2024/2025 season was defined in February 2024). Subsequently, the Ministry of Health, based on the indications provided by the WHO, issues an update circular for the control of seasonal influenza. This year, so-called vaccines have been recommended trivalent, that is, composed of two new type A strains and a new type B strain (for professionals, the three components of the current vaccine are coded as: A/Victoria/4897/2022 (H1N1) pdm09-like virus, A /Thailand/8/2022 (H3N2)-like virus and B/Austria/1359417/2021-like virus).
The vaccine can be done from October 2024 and can be done throughout the autumn period until the end of the flu season. A single dose of the vaccine is sufficient and two doses are recommended only for children under 9 years of age. The flu vaccine coverage obviously does not give the absolute certainty of not getting sick essentially for three reasons:
- the vaccine takes about two weeks to be fully active and in that period of time you remain partially vulnerable to the virus;
- Influenza viruses undergo frequent mutations and it may happen that a minimal difference occurs between the strains used for vaccines and the pathogens in circulation;
- Sometimes older people develop fewer antibodies than younger people after administration of the vaccine and therefore they can become ill although in a milder form.
It must be said that vaccines themselves cannot absolutely be responsible for influenza illness.
How vaccines work
Vaccines have the task of simulating the attack of a pathogenic organism (viruses or bacteria capable of causing a disease) in order to activate our immune defenses, without however causing the disease. Vaccines exploit the principle of “memory” that an organism develops following an infection. In fact, when a pathogen manages to penetrate our organism, a series of cells distributed in various parts of the body, called lymphocytesintercept it, neutralize it through the production of antibodies and then they put into circulation “memory cells” that in the event of a new attack by the same “invader” they are able to remember it and activate a secondary immune responsemuch faster and more effective than the first.
The vaccine, being a preparation obtained by modifying the pathogenic organism itself in order to make it harmless, once administered to the patient is able to trigger the immune response by leaving memory cells in circulation so that, in the event of a real infection, the antibodies they will recognize the enemy and will be able to neutralize him in a short time. Vaccines can be produced by live but “attenuated” viruses or bacteria (which have therefore lost the ability to cause the disease), can be completely “inactivated” (therefore killed but with structure still intact) or they can be portions of pathogens (for example surface proteins of the virus or bacterium obtained with genetic engineering techniques). In particular they can be obtained with recombinant DNA technology which is based on the laboratory production of a specific protein of an infectious agent. Currently, both inactivated, attenuated and recombinant DNA influenza vaccines are on the market.
Who is advised to get vaccinated against the flu?
The flu vaccination can be administered by your general practitioner or by the Local Health Authority Vaccination Services. The flu vaccine is strongly recommended for some categories of people and in particular for elderly people, pregnant women, as well as people with pathologies that increase the risk of complications in case of flu. Health workers and some essential service workers are also advised to avoid putting hospitals or certain activities at risk in the most critical moments. A specific Recommendation of the Council of the European Union suggests that Member States achieve vaccination coverage against seasonal influenza in 75% of the elderly and people with particular pathologies.
The vaccine is available to many categories administered free of chargein particular to people aged 60 years or over, pregnant women, people suffering from a series of pathologies that increase the risk of complications from influenza, family members living with these people, healthy children in the age group between 6 months and 6 years included, healthcare personnel, police forces, firefighters, blood donors, farmers, slaughterers and public veterinarians.
Any side effects
It is possible that after administration of the vaccine some local side effects may occur, such as swelling and redness in the injection area, or of a systemic type such as fever And muscle pain. As regards specific precautions or contraindications, these are reported in the information leaflet of the individual product and indications must be provided by the doctor or the Vaccination Center based on the age group and characteristics of the patient.
