The science behind flu season: Why does it happen every year?

Flu season is a time of the year when many people experience the flu, a contagious respiratory illness that can lead to severe cases in some individuals. It is often characterized by fever, cough, sore throat, runny or stuffy nose, muscle or body aches, fatigue, and sometimes vomiting and diarrhea. Flu season usually happens in the fall and winter months, but why does it happen every year?

The science behind flu season is complicated, involving various factors such as the virus itself, human behavior, and environmental conditions. In this article, we will explore the different factors that contribute to flu season and why we can expect it every year.

The Influenza Virus

Influenza viruses are the primary cause of flu season. There are four main types of influenza viruses: A, B, C, and D. However, only types A and B cause seasonal flu epidemics every year. Influenza A viruses are further classified based on their surface proteins: hemagglutinin (HA) and neuraminidase (NA). There are 18 different HA subtypes and 11 different NA subtypes, and each subtype is associated with various animal species.

The influenza virus has two major mechanisms for changing its genetic makeup: antigenic drift and antigenic shift. Antigenic drift is a slow, gradual process of genetic mutations that occur in the virus over time, resulting in minor changes to the virus’s surface proteins. These minor changes can help the virus avoid recognition by the immune system, allowing it to cause seasonal epidemics.

Antigenic shift, on the other hand, is a more dramatic process that occurs when two or more different influenza viruses infect the same host and exchange genetic material. This process can result in a new subtype of the virus, which can cause pandemics if it has not previously been circulating in the human population.

Human Behavior

Human behavior also plays a significant role in the spread of influenza viruses during flu season. The flu is highly contagious and spreads through the air when an infected person talks, coughs, or sneezes. The virus can also spread by touching a surface contaminated with the virus and then touching your mouth, nose, or eyes.

During the fall and winter months, people tend to spend more time indoors, which can increase the transmission of the virus. In addition, the holiday season and colder weather may lead to more social gatherings and travel, increasing the chances of the virus spreading to different areas.

Crowded places such as schools, workplaces, and public transportation can also increase the likelihood of transmission. In some cases, individuals may go to work or school even if they are feeling sick, which can further spread the virus to others.

Environmental Conditions

Environmental conditions can also contribute to the seasonality of the flu. Cold weather and low humidity levels can dry out the nasal passages, making it easier for the virus to infect the respiratory system. In addition, cold weather can cause people to congregate indoors, which can increase the transmission of the virus.

Moreover, ultraviolet (UV) radiation from the sun can damage the influenza virus, reducing its prevalence during times of the year when UV radiation is high. However, during the fall and winter, when UV radiation is low, the virus can survive longer on surfaces or in the air, increasing the chances of transmission.

Preventing Flu Season

The best way to prevent flu season is to get vaccinated. The flu vaccine is typically available in the fall, before flu season begins. The vaccine is formulated each year to protect against the influenza viruses that are expected to be most prevalent that season.

In addition to vaccination, there are several other ways to reduce your risk of getting the flu, such as washing your hands frequently, avoiding close contact with sick people, covering your mouth and nose when coughing or sneezing, and staying home if you are feeling sick.


In conclusion, flu season occurs every year due to various factors such as the influenza virus’s ability to mutate, human behavior, and environmental conditions. Understanding the science behind flu season can help us take preventive measures to reduce the spread of the virus and protect ourselves and our loved ones. Remember, getting vaccinated and practicing good hygiene habits can go a long way in preventing the flu.

Jameson Hunter

Xin chào, tôi là Jameson Hunter, một chuyên gia chia sẻ kiến thức và nhà sáng tạo nội dung với hơn 10 năm kinh nghiệm trong lĩnh vực này. Tôi sinh ngày 14/05/1989 tại Đà Nẵng, và tốt nghiệp Đại Học Bách Khoa Đà Nẵng. Tôi đam mê giải đáp và review các sản phẩm, dịch vụ trong nhiều lĩnh vực khác nhau, và luôn cố gắng chia sẻ những kiến thức hữu ích nhất cho cộng đồng. Cảm ơn vì đã đọc giới thiệu của tôi.

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