Publish Time: 2025-12-08 Origin: Bioteke
H3N2 is a subtype of influenza A virus that has recurred as seasonal influenza since causing a global pandemic in 1968.
Compared to H1N1, it has two significant characteristics:
1. Its antigenic drift is rapid, requiring annual adjustments to the vaccine; if the match is poor, the protection rate may drop to 30%–40%.
2. It poses a greater threat to the elderly, with a significantly higher risk of hospitalization and pneumonia in people over 65 years of age. Therefore, when H3N2 becomes the dominant circulating strain of the season, medical institutions often face early shortages of clinical space, with a particularly high proportion of children and elderly patients among those seeking treatment.
The key change in this year's flu is the shift in the circulating strains. The dominant strain in the previous quarter, H1N1, has fallen to a secondary position, while H3N2 has become the mainstream strain this season.
According to data from the European Centre for Disease Prevention and Control(ECDC), a new "K" subclade K variant of influenza A (H3N2) has emerged this year, and this variant has been found in multiple countries around the world. This new strain is more likely to adhere to the respiratory tract, invade the human body, and spread rapidly in schools, homes, and workplaces.
Cross-infection of multiple viruses: This year, in addition to influenza, multiple respiratory viruses are circulating simultaneously: respiratory syncytial virus(RSV), adenovirus(ADV), and others are all active. Some people have just recovered from one infection and then contracted other viruses. Some people have even been infected with influenza A and influenza B at the same time.
The 2025 influenza vaccine already covers the H3N2 strain, with a protection rate of 60% to 80%. Even if infection occurs after vaccination, the risk of severe illness can be significantly reduced. Furthermore, influenza vaccination can significantly reduce the risk of influenza outbreaks among students and other groups.
Antiviral drugs are not "miracle drugs," but they can save lives when used at the right time.
Influenza is a self-limiting disease, and most people recover on their own within 3-7 days. The value of antiviral drugs lies in reducing the probability of severe illness. Studies show that starting antiviral drugs within 48 hours of symptom onset can reduce the risk of severe illness by 60%-70%; even if more than 48 hours have passed, medication is still recommended if the condition worsens or if the person is in a high-risk group.
Common anti-influenza drugs
Oseltamivir: Oseltamivir is the most commonly used drug, mainly used to treat influenza. It needs to be taken for 5 consecutive days. Gastrointestinal reactions such as nausea and vomiting may occur, so it is recommended to take it with meals. Do not use oseltamivir for "preventative" purposes: Healthy people without symptoms or a clear history of close contact will not only find oseltamivir ineffective, but it will also increase the risk of gastrointestinal reactions and drug resistance.
If antipyretics need to be taken at the same time, it is recommended to wait at least two hours to reduce vomiting. In addition, be aware of rare side effects; less than 1% may experience neuropsychiatric symptoms (hallucinations, delirium). Parents should strengthen nighttime supervision of teenagers after they take the medication, and seek medical attention immediately if any abnormalities occur.
Marbaloxavir tablets require only a single oral dose, offering convenience but at a higher price. They are suitable for adults at high risk of influenza-related complications and children aged 12 and older with influenza. The dosage should be adjusted according to weight (40 mg for 20kg–80kg, 80 mg for ≥80kg).
Note!
Taking these medications concurrently with dairy products or calcium, magnesium, and iron supplements will significantly reduce blood drug concentration; a 4-hour interval is required.
Not recommended: Amantadine and rimantadine (high viral resistance rates). Antibiotics are ineffective! Influenza is a viral infection; antibiotics such as amoxicillin and cephalosporins are ineffective unless a bacterial infection is clearly confirmed.
Pregnant women: Oseltamivir is classified as FDA Pregnancy Category C, but substantial real-world data has not revealed any teratogenic risk. The WHO recommends its use when the benefits outweigh the risks; domestic guidelines list pregnant women as the "highest priority" group for this medication.
Lactating women: The concentration of oseltamivir and its active metabolites in breast milk is significantly lower than in maternal plasma. The dose ingested by the infant through breast milk is approximately 0.5% of the mother's weight-adjusted dose, far below the therapeutic dose.
Premature infants and full-term newborns: The CDC permits the use of oseltamivir 2 mg/kg/dose twice daily for 5 days in newborns aged 0–14 days; extremely premature infants with a birth weight <1500g require further dose reduction.
Danger Zone 1: Taking multiple cold medicines simultaneously, especially acetaminophen overdose, can lead to acute liver failure. Solution: Carefully read the ingredient list before use, and only take one type of medication per family.
Danger Zone 2: Overdosing in an attempt to "recover faster." Solution: Strictly follow the instructions or doctor's prescription; for children, the dosage must be calculated precisely based on weight.
Danger Zone 3: Blindly using intravenous infusions, believing that "IV drips lead to faster recovery." Solution: If oral administration is effective, intravenous infusion is unnecessary, reducing the risk of adverse reactions and cross-infection.
Danger Zone 4: Giving children adult aspirin may cause Reye's syndrome. Solution: Pediatric-specific formulations are the first choice for children's medications; aspirin is contraindicated.
1. Persistent high fever for >3 days, or fever recurring after initial reduction in fever.
2. Rapid breathing, blood oxygen saturation <93%.
3. Confusion, drowsiness, convulsions.
4. Chest pain, hemoptysis, severe diarrhea and dehydration.
5. Decreased fetal movement in pregnant women, or increased lochia accompanied by fever postpartum.
Wash your hands frequently: Use soap or alcohol-based hand sanitizer.
Wear a mask: Protect yourself and others.
Daily monitoring: Use respiratory multiplex antigen test kits for screening and self-testing.
Ventilate rooms: Keep indoor air circulating.
Strengthen your health: Get enough sleep, eat a balanced diet, and exercise moderately.
Institutional prevention and control: Conduct periodic disinfection and epidemic monitoring in schools, offices, etc.
[Reference]
Shanghai Armed Police Hospital
China CDC
European Centre for Disease Control and Prevention
Science Popularization China