Sweden 
Czechia 
GermanyFirst Influenza records
and possible epidemics
The origin of the Influenza virus and its early epidemics/pandemics remains unclear.
The oldest record associated with the possibility of an influenza epidemic/pandemic dates from about 8000 years ago in China1. However, the temporal distance and the impossibility of having direct or indirect evidence of what happened leads us to consider this first record as strongly speculative.
Later, Greek records from 412BC have been identified regarding epidemic outbreaks that could be due to influenza2. Since then, other registers have been found in the literature about possible influenza epidemics/pandemics (e.g., in the years 1580, 1729, 1830)2.
The 1918-1920 Spanish flu pandemic was one that caused the most significant damage, being estimated to have infected over half of the world population, with a mortality count between 40-50 million individuals2.
The influenza virus has only been isolated and identified in the early 1930’s by Shope3.
Further pandemics were registered2-4, such as the Asian flu (1957-1958), Hong Kong flu (1968-1970), and swine flu (2009-2010).
Characteristics
of the Influenza Virus
Total Molecular Weight5: ~3.9x106; Dimensions6: 80-120 nanometers; Composition7: Single-stranded; RNA Family7: Orthomyxoviridae.
What is the
Influenza Virus
Four types of influenza virus are identified in the scientific literature8-11.
Influenza A and B are the types mainly associated with the disease ́s seasonal epidemics; Influenza C and D are also registered to cause illness but at lower scales.
The classification of influenza A10 viruses encompasses different subtypes according to the composition of proteins in their surface, namely the hemagglutinin (H) and neuraminidase (N). So far, 18 types of hemagglutinin have been identified, along with 11 neuraminidase. The combination of these proteins could potentially form 198 different influenza A viruses, although only 131 have been identified up to the moment (e.g., H1N1, H3N2). These viruses may also be further classified according to “clades” and “sub-clades”, corresponding to “groups” and “subgroups” that identify each virus type according to different genetic compositions. Influenza A viruses are known to circulate both in humans and domestic animals.
The classification of influenza B viruses includes two main lineages: B/Yamagata and B/Victoria. These viruses can also be classified into different “clades” and “sub-clades”. Their circulation is known to occur only in humans, although rare cases have been reported in animals. In recent years, the B/Yamagata lineage has not been significantly detected globally. As a result, several countries — including those in Europe and the USA — have started transitioning from quadrivalent to trivalent influenza vaccines that include only the B/Victoria lineage.
Influenza C10 viruses are identified to have six genetic lineages. Although these viruses are considered as not posing a risk for epidemics, they may still cause mild illness or asymptomatic infection. Around 90% of the population already presents seropositivity to influenza C by 7-10 years old12.
The Influenza D9, 10,13 viruses are known to mainly affect cattle, pigs, small ruminants, horses and other animals, with no events being found on human infection or illness.”
History of Influenza
epidemics/pandemics
Two main mechanisms are identified14-17 for the changes in the influenza viruses, allowing for the recombination of antigens according to different H and N proteins: Antigenic Drift and Antigenic Shift. These comprise the changes in influenza virus genetic compositions that allow for influenza re-infection.
Antigenic Drift
This mechanism occurs within virus replication, producing small changes in the virus that originate virus with similar antigenic combinations. The accumulation of changes due to the antigenic drift may lead to the appearance of viruses with different antigenic combinations.
Antigenic Shift
This mechanism assumes a more sudden change in the influenza viruses antigen combination, for example through zoonosis. This abrupt change composes a major threat for pandemic influenza outbreaks since the population’s immunologic response may be totally unprepared to deal with the new antigenic combination of the influenza virus.
Influenza
Signs and Symptoms
Influenza (flu) is only one of many types of respiratory diseases caused by virus infection18, such as the syncytial virus, rhinovirus, coronavirus, adenovirus, among others.
There are several signs and symptoms associated with influenza and other respiratory infections18-23, such as: fever, cough, headache, muscle and joint aches, fatigue, sore throat, runny nose.
The signs and symptoms between some respiratory diseases often present similarities, such as COVID-19, Influenza (Flu) and Common Cold.
| Signs and Symptoms | COVID-19 | Influenza (Flu) | Commom Cold |
|---|---|---|---|
| Fever | Common | Common | Rare |
| Aches | Common | Common | Sometimes |
| Chills | Common | Common | Rare |
| Fatigue | Common | Common | Sometimes |
| Sneezing | - | Sometimes | Common |
| Cough | Common | Common | - |
| Stuffy Nose | Rare | Sometimes | - |
| Store Throat | Sometimes | Sometimes | Rare |
| Headache | Sometimes | Common | |
| Shortness of Breath | Common | Rare | - |
| Diarrhea/Vomiting | Sometimes | Common | - |
| Loss of taste/smell | Common | Rare | Rare |
Sources: ECDC21 & WHO23.
Influenza (Flu) is not an aggravated form of the common cold.
Although influenza is registered to cause mild to severe illness, it may also lead to death18, with high-risk groups being more vulnerable to aggravated forms of illness (e.g., elderly, pregnant women, young children, individuals with chronic and immunosuppressive health conditions.
Evolution of the
influenza vaccination
Influenza
burden of disease
The WHO estimates that seasonal influenza is responsible for around
one billion infection cases worldwide,
including 3 to 5 million cases of severe illness and
between 290,000 and 650,000 respiratory deaths each year28-29.
Influenza is also identified
in the literature
to aggravate underlying health conditions and exert consequences in different
health domains 28 such as cardiovascular, neurological, renal, respiratory and diabetic complications.
It is estimated 28 that influenza losses of around
24,3 quality-adjusted life years
and 2.9 million absences
(average of 3.6 days at work and 2.4 days at school)
per influenza season.
The economic burden of influenza in Europe is estimated between
6-14 billion euros per year.
Influenza prevention
through vaccination
The effectiveness of influenza vaccination is estimated between 40-60% to reduce the risk of developing flu illness in the general population30-32. However, it must be noted that these values are influenced by patient characteristics (e.g., age, health conditions, etc.), matching between circulating influenza viruses and administered seasonal influenza vaccination, among other aspects.
Demystification of resistances to influenza vaccination
Influenza vaccination
as the best prevention tool
for the disease
Vaccines were one of the great contributions to human health in controlling diseases, some that were managed to be eradicated. Currently, there are over 20 vaccine preventable diseases36-37, some of which being: smallpox, diphtheria, measles, mumps, rabies, tetanus, pertussis, yellow fever, meningococcal disease, diseases caused by human papillomaviruses, polio, among others.
Vaccines work at two levels, reducing the likelihood of contracting the disease, and if one contracts the disease, offering higher protection against severe forms of the disease than without vaccination38. However, vaccination is not a guarantee of 100% protection since its effectiveness depends on different factors (e.g., age and health conditions).
Vaccines should not be seen as a panacea for all disease-related problems38-39 but always used in articulation with a set of preventive mechanisms, such as:
NPM
Personal hygiene, surface cleaning, use of masks in respiratory infections, reduction in the presence of environmental disease vectors (e.g., infections transmitted by mosquitoes), among others.
Education
for health literacy.
PROMOTING
Understanding of culturally influenced health risk perceptions.
