If you treat the flu and a cold, the illness will last a week; if you don’t treat it, it will last seven days. How accurate is this folk wisdom, and what else do we not know about this well-studied ailment?
A Familiar Stranger
The flu is an acute respiratory viral infection that has been known to humanity for thousands of years. Hippocrates described an outbreak of “Perinthian cough” as early as 412 B.C.: this ancient physician left written evidence of a respiratory illness with flu-like symptoms. A similar illness, dubbed “peasant fever,” broke out in England in 1173. Mass outbreaks of flu have been recorded since the 16th century. In Europe alone, three epidemics of this disease were documented in the 18th century. One of them, from 1781 to 1782, is considered the largest in history, infecting over three-quarters of the population of England.
Although the flu viruses were only isolated in laboratories in the 20th century (the influenza A virus in birds in 1901, the influenza A virus in pigs in 1931, and the influenza A, B, and C viruses in humans in 1933, 1940, and 1951), the name for this illness, influenza (which translates from Italian as “influence”), spread to European languages from Rome as early as the mid-18th century. According to one theory, the term influenza indicates the potential virulence of the infection, a threat to the health of the population.
Another theory suggests that the name from the Renaissance era referred to the disease as a result of unfavorable astrological influences. The second European name for the infection, “flu” (in French, alongside die influenza, it is la grippe; in German, it is die grippe), may derive from the word “to catch.” In Slavic languages, “flu” sounds similar to the word “wheeze,” which also evokes associations with the symptoms of the illness.
Despite the fact that flu is caused by specific viruses (over 2,000 modifications are known today), flu symptoms can also appear in other acute respiratory viral infections (ARVI). Due to this similarity, they are referred to as “flu-like illnesses.” More than 200 types of respiratory viruses (rhinoviruses, adenoviruses, respiratory syncytial viruses, etc.) can cause similar conditions. Therefore, it is incorrect to refer to any ARVI as “the flu.”
Flu Pathogens
Flu viruses are divided into three types, differing in their transmission strength and severity of illness. The most common cause of seasonal flu is the influenza A virus, which is considered the most dangerous because it infects both humans and animals, transmitting from person to person, from humans to animals, and birds, and vice versa. This form of the virus is regarded as the most life-threatening, as it consists of genomes from both humans and animals. The influenza A virus causes severe and moderate illness. It is the only type of flu virus capable of causing pandemics.
The influenza B virus can only trigger localized outbreaks in specific regions. While influenza A epidemics occur every 2 to 3 years, those caused by influenza B happen once every 4 to 6 years. Influenza B infections can occur before or simultaneously with influenza A and are observed only in humans (primarily in children). The influenza C virus can also threaten only humans—children and immunocompromised adults. It often manifests alongside influenza A, but this virus does not cause epidemics or complications; the illness typically runs mild or may not present any symptoms at all.
Despite the well-founded belief in the high contagiousness of the flu, which spreads easily through respiratory droplets (during coughing, sneezing, or talking), its virus forms a lasting immunity in individuals. The cause of illness is usually a state of weakened immunity, in which people become quickly infected. Although all age groups are susceptible to the flu, the highest risk is among those aged 65 and older, followed by those aged 50 to 64. In addition to older adults, children, pregnant women, and individuals with chronic heart and lung diseases are also at high risk of infection.
Seasonal Nature
The peak of flu infections occurs during thaws: at temperatures around 0°C, the virus can survive for a month. The highest risk of infection is at temperatures between -5°C and +5°C. A combination of cold and dry airways creates favorable conditions for the virus to enter the body when humidity decreases. The recurrence of illness and the likelihood of annual seasonal flu outbreaks (typically in winter and fall) result from the virus’s variability: a consequence of antigenic drift and antigenic shifts. Research indicates that the frequency of epidemics is linked to the frequent changes in the virus’s antigenic structure while it exists in natural conditions. Due to the virus’s frequent variability (it changes its form every year), new strains of the disease with more pronounced symptoms emerge annually.
Primarily affecting the upper respiratory tract and bronchi (less frequently the lungs), the flu stands out among other viral infections for its potential for severe progression and high mortality during epidemics, which occur almost every year in the fall and winter, affecting 8% to 15% of the population. Each year, up to 500 million people worldwide are infected, with 2 million of them dying. In terms of mortality, the flu ranks eighth among all diseases (between diabetes and kidney diseases), so it should not be taken lightly.
Meanwhile, the vast majority of people infected with the flu do not seek medical help. According to an analysis of illness rates from 2005 to 2011 (data from The Lancet Respiratory Medicine), flu symptoms were observed in only one-fifth of patients, and only 17% of them consulted a doctor. At the same time, all virus carriers spread it during their illness: through aerosol transmission, an infected person, even with mild symptoms, is a source of infection from the first hour to the 5th or 7th day of the illness. This is why it is crucial to isolate the sick during flu season, wear masks, and avoid crowded places. Due to the virus’s constant mutation, medicine still lacks foolproof antiviral medications, and to achieve herd immunity through vaccinations, 80% of healthy individuals and 90% of at-risk populations need to be vaccinated.
Flu Symptoms
The flu can manifest as an infection of the upper and lower respiratory tracts, showing signs of illness 1 to 4 days after infection. Diagnosing the flu is complicated by the similarity of initial symptoms to those of other respiratory infections. Because flu symptoms resemble those of other ARVI, confirming the illness can only be done through laboratory tests. Identification of the flu virus is possible from the epithelial cells of the nasal mucosa, throat swabs, or through blood tests. In nonspecific laboratory studies, flu virus diagnosis is conducted through blood and urine analysis. A chest X-ray is mandatory during examination to detect flu complications.
Without conducting tests, the flu is diagnosed based on epidemiological data regarding simultaneous illness among other residents in the area. Flu manifests acutely with an incubation period of 3-24 hours to 2-5 days from the moment of infection (on average, this is about 1-2 days).
The main signs of the flu include:
- high body temperature (antipyretics may not alleviate it for a week), fever;
- increased weakness;
- muscle and joint aches;
- severe headache;
- nasal congestion;
- dryness in the nasal cavity and throat;
- throat and trachea pain (in the chest area);
- persistent cough;
- excessive sweating;
- tearing;
- light and noise sensitivity;
- skin rashes;
- loss of appetite.
In addition to the above, symptoms may include decreased sensitivity in the nose, dizziness, dry mouth, a sickly shine in the eyes, ringing in the ears, coating on the tongue and lips, cracks in the corners of the mouth, rapid breathing, high pulse, and irritability. Periodically, the patient’s condition may either improve or worsen.
How Long Does the Flu Last?
Depending on the degree of intoxication, overall health, age, and previous experience with the flu, the illness can take a mild, moderate, or toxic form. In mild cases, the flu may not raise the temperature at all (it may be normal or slightly lowered) or may increase to 38 degrees. In moderate cases, the temperature rises to 38.5-39.5 degrees. In severe toxic forms of the flu, body temperature can reach 40 degrees. In this state, the patient may suffer from seizures, vomiting, nosebleeds, and hallucinations.
Stomach pain and diarrhea are not mandatory symptoms of the flu, although they occur quite frequently with colds. However, they may indicate another virus. For example, gastroenteritis is most often caused by rotavirus, which, when multiplied, causes inflammation of the gastrointestinal tract. Stomach or intestinal flu should not be confused with regular flu: rotavirus infection is treated differently. Characteristic signs of stomach flu include severe vomiting and dehydration.
While flu symptoms are similar to those of other ARVI, there are also differences. In viral infections, the temperature sharply rises to a maximum immediately, while in colds, it does not exceed 38 degrees. Instead, colds are characterized by severe nasal congestion, while in the flu, it is practically absent: the nose is blocked. During ARVI, the patient often sneezes, but their eyes generally do not tear or redden, and there is usually no cough. In contrast, a flu cough can persist for more than two weeks.
A person with the flu is considered most contagious on the 3rd to 4th day after symptoms appear. If the illness is not complicated, the temperature may last for 2-4 days, and recovery occurs within 7-10 days. Most people overcome flu symptoms within a week without medical assistance. However, in severe cases, flu treatment can last up to 15 days. Weakness, irritability, sleep disturbances, and headaches may persist for two to three weeks after recovery.
Treatment of the Flu
Fever up to 38 degrees should not be reduced with medications: the body must activate its protective mechanisms independently in the fight against the virus. Flu treatment should not be conducted without consulting a doctor, as this may lead to complications.
Patients are prescribed:
- antihistamine tablets;
- nasal sprays and drops to relieve congestion and cold symptoms;
- isotonic water for rinsing the nasal cavity and vasoconstrictor drops;
- medications for throat irritation and pain;
- cough suppressants to reduce mucus viscosity.
Until the 1960s, people did not know specific medications to combat the virus and only used symptom-relief medications. Today, flu treatment still relies on various combinations of symptomatic agents—disinfectants, hemostatics, and analgesics.
It is essential to maintain fluid balance and drink 2 liters of water daily during illness. Helpful remedies for the flu include rosehip tincture, fruit drinks, lemon tea, and other warming beverages rich in vitamin C. Fluids will help expedite the elimination of toxins produced by the virus from the body.
Home remedies for the flu include:
- gargling with herbal infusions—chamomile, eucalyptus, sage, coltsfoot;
- aromatherapy with essential oils of lavender, eucalyptus, peppermint, rosemary, chamomile, and lemon;
- alkaline-oil inhalations.
Antiviral medications should be started before clinical manifestations of the flu appear: delayed administration is not effective. Antibiotics are not used in the treatment of flu as a viral infection: antibacterial medications will not help defeat the virus; their use is justified only in cases of inflammatory and purulent complications, such as pneumonia, bronchitis, otitis, or sinusitis.
In addition to bacterial infections, the flu can provoke complications affecting the cardiovascular or nervous systems (meningitis, encephalitis, etc.). For the flu to pass without a trace, it is crucial for the patient to adhere to bed rest. Patients are advised against getting up, sitting at the computer, reading, or watching television. All of these activities add extra strain that exhausts the body.
Reasons to call a doctor include:
- loss of consciousness;
- breathing difficulties (shortness of breath), especially in children: a critical condition is the ability to breathe only when leaning forward;
- pain during coughing in the side rib area (right and left);
- coughing up pink mucus (with blood);
- if high body temperature does not decrease after three consecutive doses of different medications (considering the action time of the drugs);
- if body temperature drops to 37-37.5°C and then rises again to 38°C or higher: this is a sign of a secondary infection.
In most cases, a fatal outcome from the flu is likely among infants under 2 years old and elderly individuals aged 65 and older. In such cases, do not hesitate to call for emergency assistance.
Flu Prevention
To prevent illness before the expected surge of seasonal disease, vaccination or antiviral medications make sense. However, the virus must be stopped before it arrives. To avoid seasonal flu, vaccinations should be administered in October: this allows the body to develop immunity—acquire protective properties to combat the virus—before the cold weather sets in. Interferon and immunoglobulin are used for emergency flu prevention when necessary.
Antiviral medications can support the health of unvaccinated individuals if the infection penetrates a closed environment or during an epidemic. This preventive measure can be recommended for at-risk individuals. Antiviral drugs reduce the number of clinical manifestations and shorten the duration of the illness. These pharmaceutical agents should be taken as prescribed by a doctor. The course of treatment lasts 1-2 months.
It is crucial to prevent the virus from entering mucous membranes. Regularly ventilating rooms, humidifying the air, taking warm baths, and rinsing the nose with saline solution will be beneficial in preventing illness. The flu virus is not afraid of frost but is killed by regular soap, drying, and temperatures above 70°C.
Reducing contact with sources of infection, getting fresh air, maintaining hygiene, and strengthening immunity will help prevent infection. Eliminating harmful habits, avoiding stress, getting enough sleep, eating a balanced diet, and leading an active lifestyle are just as important in combating the flu as disinfection and clean hands.