If there is one thing that you can count on every year, it’s seeing the signs reminding you to get a flu shot as we approach flu season.

This can be confusing to some, as we receive most of the vaccines only once  with an additional booster. Before the emergence of Covid-19, no other shot requirs an annual dose, so why does the flu shot?

The reason for this lies in the quickly evolving nature of the influenza virus, and its many strains.

Seasonal Flu Shot: What Is It?

The influenza vaccine, also known as the flu shot, is a vaccine that protects against the four influenza viruses that are expected to be the most common during the upcoming flu season. These four viruses are predicted based on research.

Flu shots are most often given through a needle, but there are nasal spray vaccine options.

There are also different flu vaccines available intended for certain demographic groups. For example flu vaccines authorized for use in children who are only six months old or for those over the age of 65.

A Brief History of The Flu Shot

In the 1930s, influenza viruses were first isolated from people, showing that avirus was the cause of influenza, not bacteria.

Creating the Flu Shot

The flu shot research began with the support of the U.S. Army, due to their significant loss of troops from the flu during WWI. This is because soldiers shared closed quarters, which maked it easier for illnesses to spread.

The very first flu vaccine utilized fertilized chicken eggs, a method that is still common for producing most flu vaccines today.

In 1940 the influenza B viruses were also discovered, and just two years later, a vaccine that offered protection against both the influenza A and influenza B viruses was produced.

Influenza Strains

In 1947 there was a seasonal flu epidemic, which caused scientists to realize that the influenza viruses undergo changes in the antigens they produce, resulting in unsufficent protection of the flu shot. Antigens are the parts of the virus that trigger your body to create an immune response. When the body detects an antigen, it creates antibodies that mark this specific antigen for elimination by other immun cells.

Vaccines work in a similar way; by causing the body to produce antibodies for a specific antigen. However, since the influenza virus constantly changes itself along with its antigens, antibodies for one strain will not provide sufficent protection against another strain.

This was the first discovery that led to seasonal flu vaccines based on the most common strains.

Monitoring Strains

In 1952 the World Health Organization (WHO) created the Global Influenza Surveillance and Response System (GISRS), which monitors the influenza virus evolution.

Since then, there has been a long history with the influenza virus, including finding avian and swine variants and working through multiple pandemics.

Who Should Get a Seasonal Flu Shot?

Everyone over the age of 6 months can get an annual flu shot. However, as some groups are more susceptible to contracting the flu and becoming sicker when infected with it. Therefore the flu shot is highly recommended to the following patient groups:

• pregnant women
• those over the age of 65
• those with chronic debilitating diseases

It is especially recommended for those who fit the above categories to receive a flu shot, although everyone can benefit from it.

There are some rare instances in which someone should not receive a flu shot because of their health, age, or allergies. For example, those younger than six months, or those with allergies to any component of the flu vaccine, should not receive a flu shot. Your doctor can provide more information on if the flu shot is safe for you.

The Importance of Flu Prevention

There are many strains of the influenza virus, but the flu shot protects mainly against the four viruses that are predicted to be the most common.

Can you be unlucky enough to get the flu shot and then still get the flu? Unfortunately, yes, that is possible. If you contract a strain of the virus that was not covered in the flu shot, then you can still get the flu. However, by receiving protection against the four most common strains, you significantly reduce those chances.

Additionally, if you do end up getting the flu, multiple studies have shown that being vaccinated reduces illness severity. So, even though there is still a chance of you getting the flu, it won’t be as severe.

However, getting the flu shot once is not enough for upcoming flu seasons. To truly protect yourself and others, you need to get the flu shot each year. This is because the influenza viruses adapt constantly, and so last years flu shot offers different and most likely insufficent protection the year after.

Additional Benefits

The flu shot has also been associated with lower rates of certain cardiac events in people with heart disease. This is especially true for those who have had a cardiac event in the past year.

Getting your flu shot can also help reduce the risk of worsening preexisting chronic lung diseases due to the flu, which then often lead to hospitalization.

The flu vaccine is also recommended for those who are pregnant. Not only to protect the mother during her pregnancy, but also the baby during their first few months of life. This is a time when the baby is otherwise too young to receive a vaccination themselves.

The Flu Shot: Improving Public Health and Saving Lives

Overall, the flu shot is a valuable tool for public health that offers protection against the four most common strains of the influenza virus. Not only does this protect those who are vaccinated, but it also protects those who are unable to be vaccinated themselves.

There is a chance of still getting the flu, even if you have had a flu shot. This is because there are many different flue strains, and only the four most common can be included in the vaccine. However, the flu shot still offers benefits, such as reducing the severity of symptoms and lessening the risk of hospitalization.

The influenza virus has a long history of causing multiple pandemics, with a high burden on the Swiss health care system, showing the importance of doing your part to protect yourself and those around you from the flu. When it comes to this flu season, be sure to get your flu shot to lessen your chances of getting the flu and reducing the risk of severe infection should you still get infected.

We may not be able to get rid of influenza viruses completely, but getting a flu shot every year is your best protection for you and your loved ones.

Resources

1. Ferdinands, J., Thompson, M., Blanton, L., Spencer, S., Grant, L., & Fry, A. (2021). Mildert die Grippeimpfung den Schweregrad von Durchbruchsinfektionen? Ein narrativer Überblick und Empfehlungen für weitere Forschung. Vaccine, 39(28), 3678-3695. doi: 10.1016/j.vaccine.2021.05.011
2. Grippe (Influenza). Geschichte der Grippepandemie 1930 - heute. (2019). https://www.cdc.gov/flu/pandemic-resources/pandemic-timeline-1930-and-beyond.htm
3. Bouvier, N., & Palese, P. (2008). Die Biologie der Grippeviren. Vaccine, 26, D49-D53. doi: 10.1016/j.vaccine.2008.07.039
   Smith, D., Lapedes, A., de Jong, J., Bestebroer, T., Rimmelzwaan, G., Osterhaus, A., & Fouchier, R. (2004). Mapping the Antigenic and Genetic Evolution of Influenza Virus. Science, 305(5682), 371-376. doi: 10.1126/science.1097211