On 30/1, Doctor Dao Huu Than, Head of the Infectious Disease Control Department at the Hanoi Center for Disease Control, stated that Lunar New Year (Tet) is typically a period when flu cases rise due to increased travel and social gatherings. He explained that before, during, and after Tet, people travel to their hometowns, visit relatives, attend festivals, go shopping, move between regions and provinces, and even cross international borders. This extensive movement facilitates a more rapid spread of the flu.

Beyond social factors, daily routines often change significantly during Tet. People tend to stay up late, get less sleep, consume more protein, sweets, fatty foods, and alcohol. These seemingly minor changes can lead to fatigue, metabolic imbalances, and a weakened immune system, creating favorable conditions for the flu virus to enter the body and cause illness.

In addition to lifestyle factors, the unpredictable weather at the beginning of the year, including deep cold temperatures, especially in the northern region, helps the flu virus survive longer and spread more widely within the community.

Continuous gatherings are one of the factors that cause the flu virus to spread faster during Tet than on normal days. Photo: ShutterStock

Doctor Dao Huu Than emphasized that this year's early flu season presents notable developments. In the 2025-2026 flu season, a new variant of the A/H3N2 flu virus, known as the K variant, has emerged as the predominant circulating strain in many countries across Asia and globally. Data from the global flu surveillance system indicates that from 5-11/2025, the K variant accounted for approximately one-third of recorded H3N2 flu cases. By 12/2025, this strain had been detected in over 34 countries. Based on regional transmission trends and global warnings, Doctor Dao Huu Than believes it is highly probable that the K variant of A/H3N2 is currently circulating in Vietnam. He advises the public not to be complacent and to proactively implement preventive measures.

The K variant of A/H3N2 features significant structural changes compared to previous strains, which enhances its transmissibility. "To date, there is no evidence that the K variant causes more severe illness than previous A/H3N2 strains. However, people still need to be aware and cautious, as A/H3N2 flu in general can still lead to severe disease," Doctor Than stated.

The progression of A/H3N2 infection is not uniform across all individuals. According to medical literature, this flu strain often significantly increases the risk of hospitalization in older adults, especially those aged 65 and above. Monitoring data from the US shows that this age group accounts for approximately 50-70% of hospitalizations and 70-85% of flu-related deaths.

For children, particularly those under 5 years old, the risk of hospitalization due to H3N2 flu is also higher compared to older children. The highest hospitalization rate is observed in infants under 6 months of age, an age group too young to receive the flu vaccine. Beyond causing respiratory illness, H3N2 flu can also lead to neurological complications and increase the risk of secondary infections. This risk is further elevated in premature infants or those with underlying conditions such as bronchial asthma, heart disease, neurological disorders, or obesity.

Pregnant women are also more susceptible to complications when infected with flu. Flu infection can increase the risk of hospitalization, severe respiratory complications, premature birth, and even miscarriage. The hospitalization rate due to H3N2 flu in pregnant women is about three times higher than in non-pregnant individuals. Another high-risk group includes people with underlying conditions such as cardiovascular disease, kidney disease, lung disease, diabetes, or obesity. In this group, the hospitalization rate when infected with H3N2 flu is approximately seven times higher than in healthy individuals.

To prevent illness, Doctor Dao Huu Than advises people to take proactive measures early: wash hands frequently, wear masks in crowded places, cover their mouths when coughing or sneezing, maintain a balanced diet and adequate rest, get the flu vaccine as early as possible, and seek medical attention immediately if any unusual symptoms appear.

"Regarding vaccination, the current flu vaccine remains effective against the circulating K variant of A/H3N2. Real-world data from the UK in autumn 2025 showed that the vaccine still significantly reduced the burden of disease caused by the K variant. In children, the risk of hospitalization or emergency visits decreased by 72-75%, while in adults, this risk decreased by 32-39%," the doctor reported.

Notably, the quadrivalent flu vaccine has demonstrated protective efficacy against four flu virus strains, including A/H3N2. A study by Greek scientists conducted at a maternity hospital in Athens, Greece, during the 2018-2019 flu season involving 423 pregnant mothers, revealed that the quadrivalent flu vaccine helped reduce the risk of flu by 72% and the risk of flu-related hospitalization by 86% for the mothers. The mothers subsequently gave birth to 446 infants (including cases of twins and triplets). The research team followed the infants for the first 6 months of life and found that babies whose mothers were vaccinated against flu during pregnancy had a 64,5% reduced risk of contracting flu and a 65% reduced risk of needing a doctor's visit for flu. Thus, maternal vaccination during pregnancy helps transmit antibodies to the fetus, protecting the baby during the first 6 months of life when they are too young to be vaccinated.

Kim Anh