Warning of the risk of dengue fever outbreak out of season

Dengue fever lurks before the unseasonal rains

Although it is the dry season in the South, some areas have experienced unseasonal rain, as predicted by the National Center for Hydro-Meteorological Forecasting. According to experts, climate change causes extreme weather patterns such as La Nina to increase the rate of unseasonal rain, leading to humidity, creating favorable conditions for dangerous disease vectors to thrive, especially Aedes mosquitoes - the main agent transmitting dengue fever.

Meanwhile, according to the forecast of the national meteorological agency, the weather in the North will have sunny days in the afternoon, then turn to drizzle and light rain the next day. Temperatures will sometimes be above 20 degrees, creating favorable conditions for Aedes mosquitoes to develop. The North is also entering a humid period, with increased humidity, creating conditions for mosquito eggs to hatch faster.

What is worrying is that Aedes eggs can survive in dry conditions for months and constantly adapt to environmental conditions. Therefore, even when the dry season lasts long or the weather is cold, the mosquito population still quietly maintains and waits for a favorable opportunity to breed. Rain creates stagnant water and water-holding objects, creating ideal conditions for mosquito eggs to hatch and develop.

For many years, dengue fever has not been a disease exclusive to the rainy season. According to statistics from the Department of Disease Prevention, in just the first 2 months of 2025, Ho Chi Minh City recorded 4,213 cases of dengue fever, even though it was not yet the rainy season. The situation in the North of our country is also alarming when in the cold spell in early 2025, Hanoi still recorded 137 cases. Previously, in 2023, Hanoi also recorded twice as many cases of dengue fever as Ho Chi Minh City.

In addition, during the changing seasons, not only dengue fever but people also face the risk of contracting other dangerous infectious diseases, such as influenza and hand, foot and mouth disease. Specifically, in January 2025, Hanoi recorded 820 cases of influenza, an increase of 51 cases compared to the same period last year. Meanwhile, from February 24, 2025 to March 22, 2025, Ho Chi Minh City recorded a 62% increase in the number of hand, foot and mouth disease cases compared to the average of the previous 4 weeks.

New challenges in preventing and controlling dengue fever

In a discussion on effective measures to prevent and control dengue fever held at the end of 2024, Prof. Dr. Vu Sinh Nam - Senior Advisor on Dengue Fever, National Institute of Hygiene and Epidemiology, General Secretary of the Vietnam Preventive Medicine Association, stated that the prevention and control of dengue fever in Vietnam is still very difficult to completely resolve. The four main challenges listed by the professor include: climate change, trade development, urbanization and lack of specific treatment drugs.

Prof. Dr. Vu Sinh Nam - Senior Advisor on Dengue Fever, National Institute of Hygiene and Epidemiology, General Secretary of Vietnam Preventive Medicine Association

Although Vietnam has applied biological measures such as killing mosquito larvae for many years and achieved certain results, completely eliminating mosquitoes that transmit dengue fever is not a simple task, according to experts.

More worryingly, dengue fever often starts with non-specific symptoms such as fever, headache, muscle pain, which can be easily confused with other diseases, or even have no obvious symptoms, leading to delayed diagnosis and increased risk of the disease becoming severe and spreading rapidly in the community. In addition, the subjective mentality that the disease only appears during the rainy season or is only contracted once in a lifetime, also contributes to a significant increase in the number of infections and severe cases.

Faced with the complicated developments of dengue fever, Prof. Dr. Vu Sinh Nam said that vaccines are an important tool in disease prevention. However, he emphasized that relying on vaccines alone is not enough, because mosquitoes, larvae and viruses still exist, maintaining the risk of spreading. Therefore, vaccination needs to be closely combined with traditional measures such as mosquito eradication and larvae removal to ensure long-term and sustainable disease control.

The World Health Organization (WHO) also recommends that dengue vaccination be integrated into an overall disease control strategy. This strategy includes vector control, effective case management, awareness raising and active community participation. Comprehensive vector control remains important, as the dengue-carrying mosquito poses a threat not only with the dengue virus but also with other dangerous diseases.

It is forecasted that by 2025, dengue fever and other infectious diseases will continue to develop complicatedly, becoming a major challenge for global health. Synchronous combination of measures will help reduce the spread of dengue fever, while ensuring effective and sustainable disease prevention.

This information is for informational purposes only; should not be used to diagnose or treat a health problem or disease; and is not intended to be a substitute for consulting with a physician. Please consult your physician for further advice.

Content provided by Takeda Pharmaceutical Co., Ltd., professionally approved by the Vietnam Preventive Medicine Association. C-ANPROM/VN/NON/0005, March 2025