Flu vs ARVI: how to distinguish and why it is important for treatment

Influenza and ARVI are the two most common "guests" in the cold season, which even doctors often confuse during the first examination. But behind this apparent similarity lie fundamentally different viruses, different rates of development, different risks of complications, and, most importantly, different approaches to treatment. If you catch the first symptoms and think, "It's just a runny nose and a slight fever — I'll rest for a couple of days and it will pass," then it's worth considering: could this be influenza? Because with influenza, "waiting" can turn into pneumonia, myocarditis, or even hospitalization. In this article, as an infectious disease physician with 15 years of experience, I will explain not only how to distinguish influenza from ARVI by symptoms but also why this difference is critical for choosing a treatment strategy — especially if there are children, elderly relatives, or people with chronic illnesses in the house. We will cover everything: from genetics to laboratory diagnostics, from mistakes in self-treatment to real data on epidemiology in Russia and the world. And yes — without "water," only verified facts and practical recommendations.

Classification of the disease according to ICD-11

According to the International Classification of Diseases 11th Revision (ICD-11), influenza and ARVI belong to different categories, although both fall under the section "Infectious and parasitic diseases" (Chapter 1). Influenza is coded as BA40 — "Influenza caused by the influenza virus," and the subtype depends on the serotype of the virus: A(H1N1), A(H3N2), B/Victoria, B/Yamagata, etc. This is important: it is the serotype that determines whether the vaccine will be effective this season and what form of the disease to expect — mild or severe.
ARVI is not a single disease but a group of acute respiratory viral infections caused by more than 200 types of viruses. In ICD-11, they are grouped under the code BA41 — "Other acute respiratory viral infections." This includes: rhinoviruses (about 40% of all ARVI), coronaviruses (not SARS-CoV-2!), adenoviruses, respiratory syncytial virus (RSV), metapneumovirus, and others. Each of them has its own clinical "signature": for example, rhinoviruses almost always start with nasal congestion and sneezing, while RSV more often affects the lower respiratory tract in children under 2 years old.
It is important to understand: in medical documentation, influenza is never referred to as "ARVI," even if the patient says, "I have ARVI, but my temperature is 39.5." This is not just a formality — it is a matter of accurate diagnosis, which affects the decision about hospitalization, the prescription of antiviral drugs, and epidemiological surveillance.

History of the disease and interesting historical facts

Influenza has been known to humanity since ancient times. The first reliable description of an epidemic resembling influenza is found in Hippocrates in the 5th century BC: he describes a widespread illness with fever, cough, and muscle pain that swept through Greece and Asia. However, a real breakthrough in understanding came in the 20th century.
In 1918, the "Spanish flu" broke out — a pandemic of influenza A(H1N1) that claimed the lives of 50 to 100 million people worldwide. Interestingly, the name "Spanish flu" arose not because the virus originated in Spain (it most likely started in the USA), but because Spain was a neutral country during World War I and did not censor news about the disease — unlike other countries. Thus, the world learned about the scale of the disaster.
Another interesting fact: in 1957, the influenza virus A(H2N2) — "Asian flu" — was first isolated, which claimed about 2 million lives. And in 1968 — A(H3N2), "Hong Kong flu." These strains became the basis for the creation of modern vaccines. Today we know that the influenza virus mutates in two ways: antigenic drift (slow mutations in hemagglutinin and neuraminidase) and antigenic shift (sharp recombination of genes between human and animal strains — for example, swine or avian). It is the shift that leads to pandemics.
As for ARVI — its history is less dramatic but no less significant. For example, rhinoviruses were first isolated in 1956 from nasal swabs of patients with a runny nose. Before that, a runny nose was considered a "cold" — a result of hypothermia. Only with the advent of molecular biology methods did it become clear: behind 80% cases of "cold" are viruses, not drafts.

Epidemiology: statistics on the occurrence of the disease

According to WHO, annually, influenza affects from 5% to 10% of the adult population worldwide and from 20% to 30% of children. During the peak activity season (in the Russian Federation — usually from November to March), up to 10–15% visits to therapists and pediatricians with respiratory symptoms are registered. But only 15–30% of them are confirmed influenza. The rest are ARVI.
In Russia, according to Rospotrebnadzor for the 2024/2025 season:

• The total number of ARVI cases is about 18.7 million (an increase of 12% compared to the previous season);
• Confirmed cases of influenza — 2.4 million;
• The largest increase occurred during weeks 48–51 (December), when the incidence level exceeded the epidemic threshold by 2.3 times;
• The mortality from influenza and influenza-like conditions in the same season amounted to 1,842 cases (according to FGBUN CNII Epidemiology of Rospotrebnadzor).

The statistics by age groups are particularly alarming: among children under 5 years and individuals over 65 years, the proportion of hospitalizations for influenza is 4–6 times higher than for ARVI. At the same time, 70% of fatal outcomes occur in people with chronic lung, heart diseases, or diabetes.
An interesting point: in recent years, there has been a shift in seasonality. Previously, influenza "arrived" in December–January, and ARVI — in February-March. Now, due to changes in social practices (mask mandates, remote work, fewer contacts), the seasons are becoming less distinct, and outbreaks are more prolonged and "spread out."

Genetic predisposition to this disease

Genetics plays a role not in whether you will "get sick at all," but in **how severe** the infection will be and what the likelihood of complications is. Studies show that certain polymorphisms of immune response genes affect susceptibility to influenza and ARVI.
Key genes:

• IFITM3 (interferon-induced transmembrane protein 3): the rs12252-C variant is associated with an increased risk of severe influenza A(H1N1)pdm09. In carriers of this allele, the virus penetrates lung cells more quickly.
• TLR3 (toll-like receptor 3): mutations reduce the recognition of viral RNA, which slows down interferon production and increases viral load.
• HLA-DRB1*07: associated with a milder course of influenza, while HLA-B*27 — is associated with a high risk of myocarditis after influenza.

For ARVI, the data is less clear, but it has been established that people with a deficiency of secretory IgA (immunoglobulin in mucous membranes) more often experience recurrent rhinovirus infections. The role of the gene is also important FUT2 — it determines whether a person secretes "group substances" in saliva and mucus to which rhinoviruses attach. Carriers of the non-functional allele ("non-secretor") are less likely to get rhinoviruses.
Important: genetic predisposition is not a sentence. It merely modifies risk. Vaccination, hygiene, and timely treatment can fully compensate for this predisposition.

Risk factors for the development of this disease

Risk factors can be divided into three groups: biological, behavioral, ecological.
Biological:

• Age: children under 2 years and individuals over 65 years — due to an immature or suppressed immune system;
• Chronic diseases: bronchial asthma, COPD, coronary heart disease, diabetes, immunodeficiencies;
• Pregnancy (especially the II–III trimester): hormonal changes reduce cellular immunity;
• Obesity (BMI ≥30): adipocytes secrete pro-inflammatory cytokines, exacerbating the response to the virus.

Behavioral:

• Smoking: damages the ciliated epithelium of the respiratory tract, reducing barrier function;
• Lack of sleep and chronic stress: suppress interferon production;
• Refusal of vaccination: the most significant modifiable risk factor for severe influenza;
• Self-medication with antibiotics for viral infections: leads to dysbiosis and secondary bacterial complications.

Environmental:

• High population density (schools, offices, transport);
• Low humidity (<30%): dries the mucosa, making it vulnerable;
• Air pollution (PM2.5, NO₂): exacerbates inflammation in the lungs;
• Seasonality: cold and short daylight hours reduce vitamin D synthesis, weakening immunity.

If your task is to protect a child in kindergarten — pay attention not to "antiseptics at the doors," but to the humidity in the group and the regularity of ventilation. This works better than 10 antiseptics.

Diagnosis: symptoms, laboratory and instrumental methods

The difference between influenza and ARVI begins at the stage of taking the history. Here are the key differences:

Laboratory diagnostics:

• Rapid tests for influenza antigen (nasal swab): sensitivity 50–70%, specificity >95%. A positive result is a reason to start antiviral therapy immediately. A negative result does not exclude influenza (PCR is needed).
• Real-time PCR — "gold standard". Detects not only the type of influenza (A/B) but also the subtype (H1N1, H3N2), as well as rhinoviruses, RSV, adenoviruses. Time frame — 2–4 hours.
• Serology (ELISA for antibodies) — used retrospectively: an increase in IgG titer in paired sera (acute and recovery) confirms infection. Not for emergency diagnosis.

Radiological methods:
Chest X-ray is prescribed when pneumonia is suspected — especially if the temperature does not subside after the 5th day, shortness of breath appears, or cough with purulent phlegm. In the image, diffuse infiltration is often seen in influenza pneumonia, while focal infiltration is seen in bacterial pneumonia.
Differential diagnosis:
It is necessary to exclude:

• COVID-19 (symptoms overlap, but with coronavirus, loss of smell, diarrhea, persistent fever >7 days is more common);
• Adenovirus infection (often with conjunctivitis and lymphadenopathy);
• Mononucleosis (in adolescents: sore throat, lymphadenopathy, splenomegaly);
• Bacterial sore throat (streptococcus): without cough, with white coating on the tonsils, high temperature >39°C.

Treatment: general principles and tactics

The main rule: influenza requires specific antiviral treatment within the first 48 hours, ARVI — symptomatic therapy and immune support.
General treatment (for both):**

Pharmacological treatment:
For influenza:

• Oseltamivir (Tamiflu) — a neuraminidase inhibitor. Dose: 75 mg twice a day for 5 days. Effective if started within the first 48 hours. In children from 1 year — by weight.
• Zanamivir (Relenza) — inhalation analogue, but not recommended in case of bronchospasm.
• Baloxavir marboxil (Xofluza) — a new drug that blocks cap-dependent endonuclease. Single dose of 40–80 mg (depending on weight). Especially effective in children.

For ARVI — only symptomatic treatment:

• Antipyretics: paracetamol (up to 15 mg/kg/dose) or ibuprofen (up to 10 mg/kg/dose). Do not give aspirin to children — risk of Reye's syndrome.
• Cough suppressants: codeine - only by prescription, for dry cough without phlegm. It is better to use mucolytic agents (acetylcysteine, ambroxol) for wet cough.
• Vasoconstrictor nasal drops: phenylephrine or xylometazoline - no more than 5 days, otherwise mucosal atrophy.

Surgical treatment:
Not used directly for influenza and ARVI. But in case of complications - yes:

• Lung abscess - drainage or resection;
• Pleural empyema - thoracentesis or drainage placement;
• Sinusitis with bone destruction - surgery on the sinuses.

Important: antibiotics are prescribed ONLY for confirmed bacterial superinfection (for example, with the growth of Streptococcus pneumoniae in sputum or with pneumonia X-ray showing foci). Self-medication with antibiotics for viruses is a direct path to dysbiosis and resistance.

List of drugs used for treatment

Here is the current list of drugs registered in the Russian Federation as of 2026, with an emphasis on proven efficacy:

Please note: many "antiviral" medications in pharmacies (e.g., Anaferon, Arbidol) have no proven efficacy in large randomized studies. WHO and the Ministry of Health of the Russian Federation do not recommend them as the basis of therapy. They can only be used as an adjunct — but not instead of oseltamivir for influenza.

Disease monitoring: control stages, prognosis, complications

After diagnosis, it is important to organize monitoring. Here are the control points:

• Day 1–2: assessment of temperature, respiratory function, level of weakness. If the temperature >39.5°C and does not decrease after antipyretics — call a doctor at home.
• Day 3–4: disappearance of fever — normal. If the temperature remains >38°C — suspicion of complications (pneumonia, sinusitis).
• Day 5–7: cough should become productive and decrease. If it worsens, and there is sputum with pus or blood — urgently see a doctor.
• Day 10: complete recovery. If weakness, shortness of breath, dizziness persist — a consultation with a cardiologist or neurologist is needed (risks of myocarditis, post-viral asthenia).

Forecast:
With timely treatment of influenza in healthy individuals — favorable. Complete recovery in 7–10 days. For ARVI — 5–7 days. But in at-risk groups, the prognosis may worsen:

• Pneumonia — develops in 1–5% cases of influenza, in 0.1–0.5% of ARVI;
• Myocarditis — in 1–2 out of 10,000 cases of influenza, especially in adolescents;
• Sinusitis, otitis — more common in children with rhinoviruses and influenza;
• Exacerbation of COPD/asthma — in 20–30% of patients with chronic conditions.

The "second wave" is especially dangerous: when the temperature rises again after 5–7 days — this is a sign of bacterial superinfection. In this case, a blood test for C-reactive protein and sputum culture is necessary.

Age-related features of the disease course

Children under 3 years:
Influenza in infants often masquerades as "intestinal form": vomiting, diarrhea, without pronounced runny nose. Temperature can reach up to 40°C, seizures are possible. The danger is laryngotracheitis ("false croup"): a sharp barking cough, stridor, cyanosis. Requires immediate hospitalization.
ARVI in children often starts with rhinitis, then cough joins. RSV is the main culprit of bronchiolitis: shortness of breath, retraction of intercostal spaces, "bubble" breathing. Without treatment, oxygen therapy may be required.
Adolescents and young adults (15–40 years):**
Here, influenza manifests "classically": body aches, high fever, adynamia. But it is in this group that myocarditis most often occurs — especially after physical exertion. Therefore, a ban on sports for 2 weeks after recovery is not a recommendation, but a mandatory condition.
Individuals over 65 years:
A feature is "atypical" course: temperature may be subfebrile (37.2–38°C), but there may be confusion, weakness, drop in blood pressure. This is called "influenza without fever" and is easily missed. Risk of pneumonia — up to 30%. In such patients, even a mild runny nose requires a doctor's examination.
Pregnant women:
In the II–III trimester, the risk of hospitalization due to influenza is 4 times higher than in non-pregnant women. The virus does not cross the placenta, but hypoxia and fever can provoke premature labor. Oseltamivir is allowed from the 1st trimester — the benefits outweigh the risks.

Questions and Answers

Question 1: Can influenza be treated without antiviral drugs?**
Yes, but only in mild cases in healthy individuals. However, the risk of complications from influenza is 5–7 times higher than with ARVI. If you are unsure of the diagnosis — take a rapid test. If it is positive, start oseltamivir within 48 hours. A delay of 1 day reduces effectiveness by 30%. For the elderly, pregnant women, and those with chronic conditions — antivirals are mandatory, even if symptoms are "not that severe."
Question 2: Why does a cough persist for a long time after ARVI?**
This is not a "residual phenomenon," but a protective reaction. The virus damages the ciliated epithelium of the bronchi, and recovery takes 2–6 weeks. Coughing helps clear the airways of dead cells. If the cough is dry and painful, you can use butamirate for up to 5 days. If it is wet, use ambroxol or fluimucil. But if the cough lasts more than 3 weeks, an X-ray is needed to rule out tuberculosis or allergic asthma.
Question 3: The flu vaccine doesn't help — I got vaccinated, and still got sick. Why?**
The vaccine does not provide 100% protection, but reduces the severity of the disease by 60–80%. If you got sick after vaccination, it is likely an ARVI (the virus is not included in the vaccine), or the flu strain has mutated (antigenic drift). In any case, vaccinated people have fewer complications and hospitalizations. Vaccination is not a "guarantee not to get sick," but a "guarantee not to die."
38.5°C on the 5th day, purulent sputum, leukocytosis >12×10⁹/l.

Mistake 1: "I'll take aspirin — it will quickly reduce the temperature"**
Aspirin in children and adolescents can cause Reye's syndrome — acute liver and brain damage. Instead, use paracetamol or ibuprofen. In adults, aspirin is acceptable, but only in the absence of ulcers and hemorrhagic diathesis.
Mistake 2: "I'll keep going to work — it's just a little fever"**
The flu is not a "cold." Even with a temperature of 37.5°C, you can transmit the virus to 2–3 people in the office. The incubation period is 1–4 days, and the virus is shed 1 day before symptoms appear. Stay home for at least 5 days from the onset of illness.
Mistake 3: "I'll buy immune stimulants — I'll strengthen my body"**
Many dietary supplements and "immune stimulants" (such as echinacea, ginseng) have not proven effective against the flu in controlled trials. It's better to spend money on vitamin D3 (2000 IU/day), zinc (15 mg/day), and adequate sleep. Immunity is not "pumped up," it is supported.
Mistake 4: "I'll do inhalations with saline — I'll recover faster"**
Inhalations with saline during the flu can worsen the condition: warm moist air stimulates mucus secretion, and with mucosal edema, this leads to airway obstruction. Inhalations are allowed only with a wet cough and under a doctor's supervision.

Remember: your task is not to "recover quickly," but to "prevent deterioration." Health is not something that can be "made up later." It is like the foundation of a house: if a crack appears, it needs to be reinforced now, before the wall collapses. Be attentive to yourself and your loved ones. And yes — if in doubt, call the clinic. We are always ready to help.