The common cold, which is accompanied by a low-grade fever and body aches, is accompanied by a runny nose and cough, and the symptoms usually disappear after about a week, but the flu causes a high fever of 39 degrees or more, chills, headache, and sore throat. Every year, about 5 to 10% of the entire population contracts the flu, and caution is required as the risk of hospitalization and death due to pneumonia and cardiovascular complications is high. The flu (influenza) is prevalent from November to April of the following year. Colds and the flu are caused by different types of viruses, and the flu antigen changes every year, so an annual vaccination is necessary. This is because it is difficult to create a one-time, lifelong vaccine due to the unique characteristics of the flu virus.
The Basics: How Flu Viruses Keep Evolving
Influenza Types A and B: The Key Players in Annual Flu Epidemics
Antigenic Drift vs. Antigenic Shift: What’s the Difference?
How Flu Shots Train Your Immune System
Staying Informed and Protected: Annual Flu Shots as Part of Health Routine
The Basics: How Flu Viruses Keep Evolving
Flu viruses are notorious for their ability to evolve rapidly, which is why we face new flu strains every year. Unlike many viruses that have relatively stable genetic structures, the genetic structure of the flu virus is very unstable and mutates easily. Here are some mechanisms for how flu viruses continue to evolve:
Antigenic Drift:
As the flu virus replicates, small errors in its genetic code can occur. These errors cause the proteins on the surface of the virus, called hemagglutinin (HA) and neuraminidase (NA), to change slightly, causing the virus to become antigenically different from its original version. Over time, these mutations make it harder for the immune system to recognize and fight off the virus.
Antigenic Shift:
When two different influenza A viruses infect the same cell, their genetic material can recombine, creating a hybrid virus with a new combination of HA and NA proteins. The immune system may not be familiar with this new combination, so it often has the potential to spread widely.
Selective evolution: Flu viruses evolve in response to environmental pressures, including the immune response of the host and antiviral treatments. As flu viruses circulate, those with mutations that allow them to evade the immune system or resist antiviral drugs are more likely to survive and reproduce.
Influenza Types A and B: The Key Players in Annual Flu Epidemics
Influenza A and B are actually the main causes of the flu epidemic every year. Let’s take a closer look at each one.
Influenza A:
Influenza A virus is a virus with unique characteristics that are different from colds or the flu. Influenza A virus is divided into various types (subtypes) and periodically mutates to form new types. These mutations change the structure of the antigen so that our body’s immune system cannot recognize it, which is why a new vaccine is needed every year.
The infection route is mainly transmitted through respiratory droplets in the air. It can be transmitted through droplets emitted when an infected person coughs or sneezes, and it is highly contagious. Symptoms cause systemic symptoms such as high fever, headache, muscle pain, fatigue, cough, and sore throat. These symptoms are similar to colds, but are often more severe. Influenza A vaccines are developed every year to match new mutations, and vaccination is recommended.
Influenza B:
Influenza B has fewer mutations than influenza A, so it does not change significantly periodically. Influenza B mainly infects humans, and unlike influenza A, it does not originate from animals and spread to humans or cause co-infection with animals. Like influenza A, influenza B is transmitted through respiratory droplets, but it tends to be less contagious than influenza A, so the risk of a large-scale epidemic is relatively low.
Influenza B causes similar flu symptoms to influenza A, including high fever, headache, muscle pain, fatigue, cough, and sore throat. However, in the case of influenza B infection, children and adolescents have a higher infection rate and can experience severe symptoms. Influenza B viruses are also included in seasonal influenza vaccinations. The vaccines developed each year focus on increasing immunity by including both influenza A and influenza B.
Antigenic Drift vs. Antigenic Shift: What’s the Difference?
Antigenic drift and antigenic shift are two major mechanisms of influenza viruses, with different methods and outcomes. These differences cause influenza viruses to mutate every year, sometimes creating the risk of a new pandemic.
Antigenic drift:
Antigenic drift is the process by which small mutations in the surface proteins of the influenza virus, hemagglutinin (HA) and neuraminidase (NA), gradually accumulate. This is the natural way in which small genetic mutations occur when a virus replicates. These mutations accumulate slowly over time. They are similar to the original virus, but cause slight structural changes that make it difficult to protect against with existing immunity or vaccines. Because antigenic drift is a small change, it is the cause of seasonal flu that occurs every year rather than a pandemic.
Antigenic shift:
Antigenic shift is the process by which two different influenza viruses recombine in a host, creating a completely new type of virus. When two viruses (e.g., an animal virus and a human virus) infect an intermediate host such as an animal, their genes recombine. The combined genes create a virus with a completely new antigenic structure. The resulting virus is so different from the previous virus that existing immunity can hardly protect against it. Antigenic switching has the potential to cause a large-scale pandemic. For example, the Spanish flu (H1N1) in 1918, the Asian flu (H2N2) in 1957, and the swine flu (H1N1) in 2009 are examples of pandemics caused by antigenic switching.
How Flu Shots Train Your Immune System
Vaccines help prepare your immune system to respond effectively to viral infections. Vaccines contain parts of dead or weakened pathogens. When you get vaccinated, your immune system recognizes these pathogens. Your immune system recognizes the proteins in the vaccine as foreign invaders. In response, your body produces antibodies that target these proteins. Your immune system also creates memory cells that remember the virus. If you come into contact with the actual pathogen later, your immune system can quickly recognize and respond. The antibodies bind to the virus, helping to prevent infection and eliminate it. Because flu viruses mutate, vaccines are updated each year to match the latest strains. Scientists predict which strains are likely to become prevalent and include them in the vaccine. Training your immune system through vaccination helps prevent severe disease and reduce the spread of infection.
Staying Informed and Protected: Annual Flu Shots as Part of Health Routine
Getting a flu shot every year is an active way to protect yourself from seasonal flu. Here’s why making flu vaccination a habit can be one of the best strategies for staying healthy and supporting the well-being of your community:
Protecting Against Evolving Strains:
The flu virus is constantly changing through a process called antigenic mutation and antigenic shift. As new strains emerge, last year’s vaccine may be less effective. Getting a flu shot every year with a vaccine developed to target the most current and prevalent strains can help your immune system better prepare for the specific challenges of the season.
Reducing the Risk of Severe Illness and Complications:
Influenza can lead to serious complications, especially for high-risk groups such as older adults, pregnant women, and people with chronic health conditions. Getting a flu shot every year reduces the risk of flu-related hospitalizations and reduces the severity of symptoms for those who do get the virus.
Protecting Vulnerable Groups:
The more people get vaccinated, the less flu spread in your community. Widespread vaccination also helps protect people who can’t get vaccinated, such as young children and people with certain medical conditions.
Establishing Healthy Habits:
By incorporating a flu shot into your annual routine, you are establishing a habit that prepares your immune system for flu season. By making a flu shot a part of your health routine each year, you are contributing to your own well-being and the health of those around you.
Source:
1. Why do we need new flu shots every year?
https://www.health.harvard.edu/staying-healthy/why-do-we-need-new-flu-shots-every-year
2. Flu shots have changed this year — here's whyhttps://www.livescience.com/health/flu/flu-shots-have-changed-this-year-here-s-why
3. The science behind the flu shot
https://www.geisinger.org/health-and-wellness/wellness-articles/2020/11/09/19/23/science-behind-the-flu-shot
4. Flu shot: Your best bet for avoiding influenza
https://www.mayoclinic.org/diseases-conditions/flu/in-depth/flu-shots/art-20048000