Influenza in children: features of the course, first signs, and when to run to the doctor

Influenza in children is not just a "cold, but with a fever." It is an acute viral respiratory disease caused by RNA influenza viruses (type A, B, less commonly C), which can develop rapidly and lead to severe complications even in healthy children. Unlike ARVI, influenza begins suddenly: within a few hours, the temperature rises to 39–40 °C, there is body aches, headache, sharp weakness, and cough and runny nose come later — often against a background of pronounced intoxication. In children under 5 years old, especially under 2 years old, the risk of hospitalization is higher because their immune system has not yet "learned" to recognize and block the virus as effectively as in adults. And yes — influenza can be contracted without complications, but only if it is recognized in time, not confused with other ARI, and if the development of a bacterial secondary infection is prevented.

Classification of the disease according to ICD-11

According to the International Classification of Diseases 11th Revision (ICD-11), influenza is coded as BA20 — "Influenza caused by influenza virus A," BA21 — "Influenza caused by influenza virus B," and BA22 — "Influenza caused by influenza virus C." These codes belong to the section "Infectious and parasitic diseases" → "Viral infections of the respiratory tract." Importantly, in ICD-11, influenza is distinguished separately from other acute respiratory viral infections (ARVI), which are designated as BA23 ("Other acute viral infections of the upper respiratory tract"). This is not a bureaucratic detail — it is a difference in treatment tactics, prognosis, and prevention. For example, antiviral drugs like oseltamivir specifically act against influenza viruses A and B, but not against adenoviruses or rhinoviruses, which most often cause the typical "cold."
If you see the code BA23 in the medical history, it is not influenza, but another ARVI. And if the doctor diagnosed "influenza" without confirmation (for example, without a rapid test or PCR), it is worth clarifying: it may be a clinical probability rather than a laboratory-confirmed case. During the peak flu activity season (January-February), doctors often diagnose it based on characteristic symptoms, but it is better to have confirmation for antiviral therapy — especially in children with chronic diseases.

History of the disease and interesting historical facts

Influenza has been known to humanity since ancient times. The first reliable descriptions of mass outbreaks date back to the era of Ancient Rome and Greece — Hippocrates in the 4th century BC described "fever with cough and shortness of breath," which "passed through cities like fire." However, a real breakthrough in understanding influenza occurred only in the 20th century. In 1918, the most destructive pandemic in history broke out — the "Spanish flu" (although its origin is not related to Spain). Over two years, it claimed the lives of about 50 million — more than World War I. It particularly affected young people aged 20-40, while children and the elderly — usually the most vulnerable groups — suffered less. Scientists still argue about why this happened, but one of the hypotheses is related to the "cytokine storm" — an excessive immune response in people with strong immunity.
An interesting fact is that the influenza A virus has the ability for **antigenic shift** — a sharp change in surface proteins (hemagglutinin and neuraminidase) when two different strains (for example, human and avian) exchange genetic material within one cell. This is how the pandemic strains of 1957 ("Asian flu"), 1968 ("Hong Kong flu"), and 2009 ("swine flu" H1N1pdm09) arose. These new strains are particularly dangerous for children because they have no immune "memory" against them — neither from previous illnesses nor from vaccination.
Another curious point: in 1933, British scientists first isolated the influenza A virus from guinea pigs — which is why it is sometimes called "swine flu," although in nature it circulates among birds and mammals. Today we know: influenza viruses are not static entities, but constantly mutating "genetic drifts," which makes creating a universal vaccine an extremely challenging task.

Epidemiology: statistics on the occurrence of the disease

According to WHO, annually influenza affects from 51 million to 101 million adults worldwide and from 201 million to 301 million children. In Russia, the flu season usually begins in late October - early November, peaks in January-February, and subsides by April. According to Rospotrebnadzor for the 2024-2025 year, during the epidemic rise (January-February 2025), the incidence of influenza among children under 14 years old was **187.3 cases per 10,000 child population** — almost 2.5 times higher than among adults (76.1 per 10,000).
What is particularly concerning is the share of hospitalizations among children with influenza: according to statistics from the Federal State Budgetary Institution "NMITZ Health of Children" of the Ministry of Health of the Russian Federation, in the 2024/25 season about **12-15% of children with laboratory-confirmed influenza were hospitalized**, with 3-5% developing complications: pneumonia, bronchiolitis, otitis, myocarditis, or neurological disorders (for example, seizures during fever). The highest risk is among children under 2 years old, especially premature ones, and those suffering from chronic diseases: asthma, diabetes, immunodeficiencies, heart anomalies.
Here is a table with the main indicators by age groups (data for the 2024/25 season, Rospotrebnadzor + NMITZ Health of Children):

Note: even with a decrease in the absolute number of cases compared to the 2009 pandemic, influenza remains one of the main causes of childhood morbidity and temporary incapacity of parents. And yes — vaccination reduces the risk of illness by 40–60%, and severe forms by 70–80%. But the vaccination coverage among children in Russia currently does not exceed 55% (according to the Ministry of Health, 2025), which leaves a significant part of the population vulnerable.

Genetic predisposition to influenza

There is no direct "influenza gene" — but there are genes that influence susceptibility to the virus and the severity of the course. Recent studies show that variants of genes involved in the antiviral response may determine how the body reacts to infection. For example:

• Gene IFITM3 (interferon-induced transmembrane protein 3): its mutation rs12252-C is associated with an increased risk of severe influenza in children. This protein blocks the virus from entering the cell. In carriers of the mutation, the protection is weakened.
• Gene TLR3 (toll-like receptor 3): is responsible for recognizing viral RNA. Defects in it can lead to insufficient interferon production and prolonged viral carriage.
• HLA-class II genes (for example, HLA-DRB1*07): some alleles are associated with a milder course, others — with the risk of complications. This explains why two children from the same family may experience the flu differently.

Important: genetic predisposition is not a sentence. It only increases the likelihood of a severe outcome in the presence of other factors (age, comorbidities, timeliness of treatment). To date, genetic testing for predisposition to influenza is not part of standard practice — it is used only in scientific research. But if a child has already had severe forms of ARVI or influenza, it is worth paying attention to the presence of chronic pathologies and enhancing prevention.

Risk factors for the occurrence and severe course of influenza in children

Risk factors can be divided into three groups: **biological**, **environmental**, and **behavioral**.
Biological:
— Age under 2 years (immature immune system);
— Chronic diseases: bronchial asthma, cystic fibrosis, HPV, immunodeficiencies (congenital or acquired, for example, in HIV);
— Prematurity (especially at less than 32 weeks gestation);
— Obesity (BMI > 95th percentile for age);
— Presence of neurological disorders (cerebral palsy, epilepsy) that increase the risk of aspiration and respiratory failure.
Environmental:
— Close living conditions (kindergartens, schools, large families);
— Air pollution (PM2.5, NO₂) — reduces the barrier function of the respiratory mucosa;
— Seasonality: the highest risk is in the winter months with low humidity (<30%) and a temperature of +15…+20°C indoors, which contributes to the survival of the virus in aerosol for up to 24 hours.
Behavioral:
— Refusal of vaccination;
— Late consultation with a doctor (more than 48 hours from the onset of symptoms);
— Self-treatment with antibiotics (which is not only useless against the virus but also provokes dysbiosis and resistance);
— Insufficient fluid intake and hypodynamia during illness — slow down the elimination of toxins and recovery.
If your child has at least two factors from the list — it is worth discussing with a pediatrician a plan of action in case of a rise in temperature and weakness. Don’t wait until it gets “bad” — preparation is your main shield.

Diagnosis of influenza: how to distinguish it from ARVI and when a test is needed

The main rule: **not all febrile conditions in children are influenza**. But if the symptoms started suddenly, with a sharp rise in temperature to 39–40°C, severe weakness, headache, and body aches — the likelihood of influenza is high. Especially if there are already confirmed cases in the vicinity.
Main symptoms of influenza in children:
— High fever (often without a prodromal period);
— Intoxication: lethargy, refusal to eat, crying without tears, "empty gaze";
— Muscle and joint pain (the child does not want to stand, walk, asks to be "held in arms");
— Headache (in older children — complaints of pain in the forehead, behind the eyes);
— Cough — dry, paroxysmal, appears on the 2nd–3rd day;
— Runny nose — usually moderate, later than with ARVI;
— Nausea, vomiting, diarrhea may occur (more often in children under 5 years — this is not "stomach flu," but a systemic reaction).
Laboratory diagnostics:
— Rapid influenza antigen test (swab from the nose/throat) — result in 15–30 minutes. Accuracy 50–70% (false-negative results are possible, especially if taken late — after 48 hours from the onset of symptoms);
— PCR diagnostics — "gold standard." Detects viral RNA with accuracy >95%. Done from a swab or rinse from the nasopharynx. Time — 2–4 hours in most laboratories;
— Serological method (ELISA for antibodies) — is rarely used, only for retrospective assessment (2–3 weeks after the illness).
Radiological examinations:
Not needed in mild cases. But if there are signs of respiratory failure (increased work of accessory muscles, respiratory rate >40 per minute in children aged 1–5 years), or if the temperature does not subside for 5 days — a chest X-ray is performed to rule out pneumonia. In children under 3 years, ultrasound examination of the lungs is more often used — safe and informative.
Differential diagnosis:
Influenza needs to be distinguished from:
— Adenovirus infection (often with conjunctivitis and enlarged tonsils);
— RSV (always with bronchiolitis, wheezing, in small children);
— Whooping cough (paroxysmal cough with "whooping" vomiting, but without high fever);
— Bacterial tonsillitis (angina): sore throat predominates, high temperature, but no aches and weakness in the first hours.
If in doubt — it is better to do a rapid test. It is available in clinics, some pharmacies, and emergency services. And yes — even if the test is negative, but the clinical picture is typical for influenza, the doctor may prescribe antiviral therapy empirically, especially during the epidemic season.

Treatment of influenza in children: what works and what does not

Treating influenza is not about "treating the virus," but about helping the body cope with it and preventing complications. The main principles:
1. Antiviral therapy (pharmacological):**
— Oseltamivir (Tamiflu, Nomides) — the drug of choice for children from 2 weeks of age. Dosage depends on body weight:
 • Up to 15 kg — 30 mg twice a day;
 • 15–23 kg — 45 mg twice;
 • 23–40 kg — 60 mg twice;
 • >40 kg — 75 mg twice.
Course — 5 days. It should be started within **48 hours** of the onset of symptoms — otherwise, effectiveness decreases. In children with severe illness (hospitalized), the course may be extended to 10 days.
— Zanamivir** (Relenza) — inhalation powder, approved from 5 years. Less convenient for small children, as it requires cooperation during inhalation. Effective against A and B.
— Baloxavir marboxil** (Xofluza) — a new drug, acts on a different target (cap-dependent endonuclease). Approved from 5 years, course — 1 day (one dose). But so far, there is little safety data for children under 12 — used in exceptional cases.
2. Symptomatic therapy:**
— Antipyretics: paracetamol (from 1 month) or ibuprofen (from 6 months). The dose is strictly by weight: paracetamol — 15 mg/kg every 4–6 hours, ibuprofen — 10 mg/kg every 6–8 hours. Never give aspirin — risk of Reye's syndrome!
— Hydration: drinking should be abundant — 1.5–2 ml per 1 kg of body weight per hour (in the first day). Better — electrolyte solutions (Regidron Bio, Gastrolit) than tea or juice.
— Cough remedies — only for dry, painful cough and only as prescribed by a doctor. Codeine and other opioids are prohibited until 18 years old. Allowed: butamirate (Sinekod), prenoxdiazine (Linkas), or herbal (Gedelix, Doctor Mom) — but with caution in allergic individuals.
3. Surgical treatment — not applied.**
Influenza — a viral infection, no operations needed. Exception — complications: for example, lung abscess or pleural empyema — then drainage is required, but this is no longer "treatment of influenza," but treatment of a complication.
4. Folk remedies and "grandmother's methods":**
— Hot foot baths during fever — dangerous: can provoke seizures.
— Garlic, onion in the nose — ineffective and injure the mucosa.
— Steam inhalations — prohibited during fever (risk of burning the airways).
— "Sweating it out" — a myth. Sweating does not eliminate the virus — it regulates temperature. Better — a cool damp wrap (not cold!) and abundant drinking.
If you think: "Maybe we should just wait it out?" — remember: in children, the flu can worsen within 12–24 hours. The "second rise" in temperature on days 4–5 is especially dangerous — this is often a sign of bacterial pneumonia. Don't wait — observe, record symptoms, and seek help in time.

Forecast:
In healthy children without chronic diseases, the prognosis is favorable — recovery occurs within 7–10 days. But it is important: fatigue and cough may persist for 2–3 weeks — this is normal if there is no fever and overall deterioration.
Complications (most common in children):**
— Pneumonia (bacterial or viral) — the main reason for hospitalizations;
— Otitis media — especially in children under 5 years old due to the anatomical features of the Eustachian tube;
— Bronchiolitis — when infected with RSV against the background of influenza;
— Myocarditis and pericarditis — rare, but dangerous: the child becomes pale, complains of chest pain, pulse is rapid;
— Neurological complications: Febrile seizures (at a temperature >38.5°C), encephalopathy (drowsiness, vomiting, speech impairment) — require immediate hospitalization.
If you notice at least one of these signs — do not delay a visit to the doctor. It's better to be safe than to treat complications later.

Age-related features of influenza in children

Influenza in a child is not a "small adult." Their body reacts differently, and symptoms may be atypical.
Children under 1 year:
— Often there is no pronounced cough and runny nose — instead, there is lethargy, refusal to breastfeed/bottle-feed, vomiting, diarrhea;
— The temperature may be "hidden" — not up to 40°C, but 38.5–39, while the child is very pale, and the skin feels cold to the touch;
— The risk of respiratory failure is high — due to weak musculature and narrow airways. Pay attention to "retraction" of the abdomen during inhalation and flaring of the nostrils.
Children 1–3 years:
— Often starts with vomiting and diarrhea — parents mistake it for an intestinal infection;
— Characteristic "breakage": the child does not want to get up, hides under the blanket, cries when touched;
— High risk of febrile seizures — especially with a rapid rise in temperature.
Children aged 4–7 years:
— Can already describe their feelings: "my head is splitting," "my whole body hurts";
— Otitis often joins — complaints of ear pain, crying when pressing on the tragus;
— Pseudocroup (laryngotracheitis) is possible — "barking" cough, hoarseness, difficulty breathing — requires immediate assistance.
Children aged 8–14 years:
— Symptoms are closer to adults: fever, headache, weakness;
— But there is a nuance: adolescents have a higher risk of myocarditis and psycho-emotional reactions (apathy, anxiety, insomnia);
— Often ignore symptoms, continue to go to school — which exacerbates the epidemic and risks their health.
Remember: the younger the child, the less specific the symptoms are. Don't wait for the "classics" — focus on the overall condition. If the child does not recognize you, does not respond to your call, breathes quickly and shallowly — this is a reason to call an ambulance.

Questions and answers: the most common inquiries from parents

Question 1: Is it possible to get a flu shot if the child already has a cold?
No, it is not possible — if there are signs of ARVI (fever, runny nose, cough), vaccination is postponed until full recovery (at least 2 weeks after the fever subsides). But if it is a mild form without fever — the decision is made by the doctor. Important: vaccination does not cause the flu — it uses inactivated or recombinant viruses that cannot reproduce.
Question 2: Why has the child's temperature been high for 5 days, but he is not getting worse?
This can be normal with the flu. Viral fever often lasts 5–7 days. The main thing is not the temperature as a number, but the condition: if the child is drinking, responding, looking into your eyes, breathing calmly — everything is fine. But if on the 5th day the temperature spikes again after a drop — this is a warning signal.
Question 3: Should antiviral medications be given if the flu test is negative?
If the clinical picture is typical for the flu (sudden onset, high fever, intoxication), and the test was done late (after 48 hours), the doctor may prescribe oseltamivir empirically — especially if the child is in a risk group. But this decision is made only by a specialist, not independently.
Question 4: How to distinguish flu from ARVI in a child without tests?
Compare based on three points:
1. Onset: flu - sudden (within 2-4 hours), ARVI - gradual (1-2 days);
2. Temperature: with flu - 39-40°C immediately, with ARVI - 37.5-38.5°C, rarely higher;
3. Condition: with flu - pronounced weakness, "can't get out of bed", with ARVI - the child plays, watches cartoons, even with a runny nose.
Question 5: Can the flu go away without treatment?
Yes, in healthy children - it can. But the risk of complications remains. Antivirals do not "kill the virus instantly", but reduce its replication, shorten fever by 1-2 days, and decrease the likelihood of pneumonia by 60%. It's like insurance - you don't know if there will be an accident, but the seatbelt will save your life.

Typical mistakes parents make when their child has the flu

1. "Let's wait until morning" with a fever of 40°C and lethargy.
- What to do: if the temperature does not decrease after taking an antipyretic, or the child does not respond, does not drink - call an ambulance immediately. Do not wait until morning.
2. Giving antibiotics "just in case".
- What to do: antibiotics do not work against viruses. They are prescribed only by a doctor when there is suspicion of a bacterial infection (purulent discharge, second rise in temperature, worsening after 5 days).
3. Bathing a child with a fever.
— What to do: a bath with water at 36–37°C is acceptable if the child is not shivering and not pale. But not hot, not with the addition of "medicinal herbs" — this does not treat and can provoke collapse.
4. Ignoring dehydration.
— What to do: count urinations. If there is no urine for 6 hours — this is a signal. Give Regidron Bio 5 ml every 2–3 minutes until they start drinking independently.
5. Return to kindergarten/school 2 days after the temperature drops.
— What to do: the child remains contagious for 5–7 days from the onset of symptoms. Even if the temperature is normal, the virus is still being shed. Wait at least 7 days — and only after consulting a doctor.

Conclusion: what is important to remember about influenza in children

Influenza in a child is not a "cold," but a serious viral infection that requires attention, but not panic. Key points:

• Recognize by sudden onset, high temperature and pronounced intoxication — not just a runny nose;
• Vaccination is the most effective way to protect yourself. Even if a different strain appears in the season — it reduces severity;
• Antiviral medications work only in the first 48 hours — do not delay your visit to the doctor;
• The main enemy is dehydration and late consultation. Keep a symptom diary;
• Don't be afraid to ask the doctor: "Is this really the flu?", "Is a test needed?", "What to do if the temperature doesn't go down?" — a good doctor will explain.

As a pediatrician with 18 years of experience, I will say it straight: most severe cases are not due to the virus, but because parents didn't trust their feelings and thought: "Well, they'll get through it." You don't need to be a hero. Take care of your child — and yourself. May this season pass without hospitalizations, without fear, and without questions like "What could I have done?". You are already doing the main thing — reading, learning, preparing. And I am always nearby, in this article and beyond. Stay healthy.