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Flu Season 2020-2021: What do you need to know before getting vaccinated?

Oct 9, 2020

The flu epidemic in the US occurs every year during autumn and winter. According to the CDC, it is estimated that the flu has resulted in between 9.3 million and 49 million illness each year in the US since 2010. In addition, 75% of influenza-related deaths in the US occur in people over the age of 65. Fortunately, there is a way to prevent it: vaccination.

During the first few months of this 2020-2021 flu season, the most vulnerable among us are called upon to be vaccinated as a priority.

But what do we need to know before getting vaccinated? Why do we need to renew the vaccine every year? Can you get the flu by being vaccinated? Why isn't the vaccine compulsory for everyone? 

We'll tell you all about it in our article!

Flu Season 2020-2021: What do you need to know before getting vaccinated?

How does vaccination work?

From a historical point of view, the idea of preventing diseases has been around for centuries. We've come a long way from the smallpox inoculation by Edward Jenner in the 18th and 19th centuries or Louis Pasteur's first rabies vaccine. Today, vaccination has become a major public health solution: thanks to vaccination, 2 to 3 million lives are saved worldwide each year according to the WHO.

Generally speaking, fighting an infection is a two-step process. Faced with a warning signal, such as the presence of an infectious agent (which may be a foreign element or the flu virus), the immune system puts in place:

  • an innate immune response that is rapid but independent of the infectious agent involved;
  • then an adaptive (or specific to the infectious agent) immune response, which is more effective but requires more time. It is during this phase that the immune system produces antibodies. It is these antibodies that will be able to recognize, neutralize and eliminate an infectious agent in a "targeted" manner.

The start of these two successive phases is slow, and often allows time for the infectious agent to cause illness.

Vaccination involves preparing the body to defend itself against the infectious agent. It consists of the preventive introduction of harmless copies of the infectious agent into a healthy (not yet infected) individual. These copies are said to be harmless because they are able to stimulate the immune system without causing disease. For example, in the case of the flu virus, an inactive fragment of the virus is added to the vaccine. 

Vaccination makes use of a remarkable feature of the immune system: immune memory. This means that, at the next exposure, the immune system will be able to quickly produce those antibodies that can recognize, neutralize and eliminate the infectious agent. In this way, the infection is controlled and eliminated before the illness sets in.

But what is the seasonal flu exactly?

Seasonal influenza is an acute respiratory infection caused by the Influenza virus of the Orthomyxoviridae family. It mainly affects the upper respiratory tract (nose, throat, bronchial tubes) and more rarely the lungs. Symptoms are grouped under what is known as an influenza-like illness (ILI) or "flu-like syndrome", i.e. aches and pains, high fever, respiratory signs (dry cough and runny nose), intense fatigue and headaches.

Note: Be careful not to confuse the flu with ILI. Flu-like syndrome is a set of symptoms that can be caused by viruses other than the Influenza virus. You can have flu symptoms without actually having the flu.

The incubation period for the flu can be up to two days, meaning that symptoms can appear up to 48 hours after infection and can persist for up to two weeks. An infected person is contagious up to five days after the first symptoms appear (note that this can last for up to seven days in children).

There are three types of Influenza virus that infect humans: types A, B and C. Only types A and B are responsible for seasonal epidemics.

  • Type A mainly infects humans and animals (avian and mammal species): type A is subdivided into several subtypes according to the composition of the virus.  

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Source: CDC

In fact, the surface of the virus is covered with surface proteins: neuraminidase (N) and hemagglutinin (H). There are several versions of these proteins, from H1 to Hx and N1 to Nx. Depending on the combination of these proteins, the subtypes will be identified as HxNy.

For example, the "H1N1" virus responsible for the 2009 pandemic refers to a type A virus, whose hemagglutinin is type 1 and the neuraminidase is also type 1.

  • Type B infects almost exclusively humans: it can be divided into two groups (or lineages), the B/Yamagata lineage and the B/Victoria lineage.
  • Type C is only rarely detected, and usually causes mild infections.

The main characteristic of these viruses is their great genetic variability: they mutate and transform over time as they infect people. This means that every year a new form of virus appears. This is why a new flu has to be fought every year, which thus explains the need to get vaccinated every year before the flu season.

The World Health Organization is responsible for determining, a few months before the flu season, which strains (i.e. subtypes of the virus) are most likely to circulate and should be included in the vaccine.

Why get vaccinated against seasonal flu? 

Seasonal flu is generally considered to be a low-risk illness, especially in young, healthy people. However, it is important to know that influenza can be serious or even fatal in some patients and that there are some people at risk. That is to say: the elderly, pregnant women, infants, obese patients or people with chronic conditions.

Getting vaccinated has a benefit on an individual level but also on a collective level. Indeed, by getting vaccinated we reduce the number of people likely to spread the virus. It protects the most vulnerable and reduces the risk of serious complications or death. It should be noted that although it is hard to estimate how many deaths exactly are prevented by the flu vaccine, researchers estimate that flu shots prevented 7 million illnesses and 8,000 deaths in the US last year. 

A few details on the flu vaccination protocol: When should you get vaccinated? Who should get vaccinated?

It is the FDA and CDC that update the immunization administration protocol for any vaccine. For seasonal flu, a single dose is recommended. The CDC recommends getting a flu vaccine in early fall (or by the end of October), just before the virus starts to circulate.

The CDC recommends vaccination against influenza for:

  • Adults 65 years and over;
  • Adults with chronic health conditions like asthma, heart disease & stroke, diabetes, chronic kidney disease, cancer, or HIV/AIDS;
  • Children 6 months and older;
  • Health and social care workers.

To learn more, you can find the complete list of people at risk: People at High Risk For Flu Complications

You should know that you are protected about two weeks after being vaccinated against the flu. It is therefore recommended that you get vaccinated every year in the fall to be protected during the winter.

For those of us who are a bit behind on things, it's not too late to get your flu vaccination! Even if the virus is already circulating, getting vaccinated against the flu helps protect yourself and others, reduces the spread of the virus, and therefore reduces the serious forms of seasonal flu, some of which are fatal in the most vulnerable people.

Can I get the flu from being vaccinated?

Before each flu season, the WHO is responsible for giving recommendations on the 3 or 4 main strains to include in the composition of vaccines. To do this, the WHO has a global surveillance and alert system to detect circulating strains of viruses. The strains circulating in humans are particularly monitored, making it possible to update the composition of vaccines twice a year. Despite this, influenza remains unpredictable, as the occurrence of an unexpected strain that is not integrated into the vaccine can reduce the effectiveness of the vaccine. The closer the chosen virus strains are to the circulating strains, the more effective the vaccine will be.

As a result, a vaccinated individual may not be fully protected. If the type of virus chosen in the composition of the vaccine is too far removed from the circulating type of virus, the vaccine will not be completely effective. This means that even a "prepared" immune system may have more difficulty recognizing a virus that has suddenly mutated. In addition, it is important to know that the protection provided by the vaccine diminishes over time.

Furthermore, it is impossible for the vaccine to cause flu in a healthy individual. In fact, the vaccine contains only an inactive copy of the virus, which is non-infectious.

So, what is the 2020-2021 flu vaccine made of?

This year the vaccines available for the 2020-2021 flu season and in accordance with WHO recommendations, the 2020 influenza vaccines are composed of the following virus strains:

  • A/Guangdong-Maonan/SWL1536/2019 (H1N1)pdm09, 
  • A/Hong Kong/2671/2019 (H3N2),
  • B/Washington/02/2019 (Victoria lineage),
  • B/Phuket/3073/2013 (Yamagata lineage).

To understand the nomenclature of viral strains decided by the WHO, here are a few pointers. Let's take one of the virus strains present in the current vaccine: A/Guangdong-Maonan/SWL1536/2019 (H1N1)pdm09.

  • A for the type of virus (thus A or B);
  • Guangdong-Maonan for the geographical origin of the isolated strain;
  • SWL 1536 for the strain number;
  • 2019 for the year of isolation;
  • H1N1 for type A, hemagglutinin and neuraminidase subtype (for type B, the lineage will be used);
  • pdm09 for pandemic 2009, as this virus caused a pandemic in 2009.

For more information: Prevention and Control of Seasonal Influenza with Vaccines: Recommendations of the Advisory Committee on Immunization Practices — United States, 2020–21 Influenza Season

This year, the following flu vaccines have been released by the FDA: Afluria Quadrivalent®, Fluarix Quadrivalent®, Flublok Quadrivalent®, Flucelvax Quadrivalent®, FlulLaval Quadrivalent®, and a few others. For the complete list: Influenza Vaccine for the 2020-2021 Season

How much does the flu vaccine cost? Where can I get it done?

Health insurers are required under the Affordable Care Act (ACA) to cover all federally recommended vaccines for patients, meaning when patients with insurance get their flu shots, it's free. Given the current public health crisis caused by COVID-19, many places are offering drive-through flu shots, including some community clinics, major hospital networks, and even grocery chains. To find a vaccination location near you, you can use the CDC's VaccineFinder.

Are adjuvants dangerous? What are they and what are they for?

In the composition of a vaccine, we often find the term adjuvants. An adjuvant is an ingredient used in some vaccines that helps create a stronger innate immune response, which is essential to activate immune memory, upon which the principle of vaccines is based.

Adjuvants are used, for example, to reduce the number of injections and to strengthen the response in weak responders (the elderly or immunocompromised people, etc.). These adjuvants are used in particular for vaccines that are not live or whose infectious agent is inactivated, as is the case for influenza.

It should be noted that if certain vaccines do not need adjuvants, it is because they are capable of inducing a sufficient innate immune response: in this case, they are said to be immunogenic.

Aluminum salts are the most widely used adjuvants, given the data in favor of their safety, with more than 90 years of use and hundreds of millions of doses injected, according to the ANSM (the French National Agency for the Safety of Medicines).

Other adjuvants are developed when aluminum is not effective, as is the case with the flu vaccine. These include MF59 (squalene oil, a naturally occurring substance found in humans, animals, and plants), bacterial derivatives or artificial vesicles called liposomes.

What are the possible side effects of the flu vaccine?

Getting a flu shot will not infect you with the flu, remembering that the infectious agent is inactive and therefore unable to make you sick with the flu.

However, like any medical product, vaccines can cause side effects. Side effects caused by the flu vaccine are generally mild and go away on their own within a few days. These include:

  • A local reaction where the vaccine was injected (soreness, redness, swelling);
  • Fever;
  • Nausea;
  • Muscle pain
  • More rarely, severe or allergic reactions can occur (difficulty breathing, hoarseness or wheezing, hives, swelling around the eyes or lips, etc.) In this case, call 911 get to the nearest hospital. Otherwise call your doctor. Afterwards, you or your doctor should report the reaction to the Vaccine Adverse Event Reporting System (VAERS).

For more information, you can consult the CDC's Flu Vaccine Safety Information.


Finally, here are some encouraging statistics...

According to the WHO, vaccination saves 2 million lives every year worldwide!

It has made it possible to eradicate smallpox, led to a 99% drop in polio cases between 1988 and 2003 and a 40% drop in measles cases between 1999 and 2003, according to INSERM.

The important thing to remember is that the influenza virus is a very particular virus, capable of mutating and transforming itself over the years. This is why, every year, vaccination against seasonal flu is a real public health challenge

Getting vaccinated is like wearing a mask during a health crisis; you protect yourself, but above all you protect others.

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Take care!

avatar Doriany Samair

Author: Doriany Samair, Digital Marketing Assistant

Within the Digital Marketing team, Doriany is in charge of writing medical fact sheets and scientific articles. She is also in charge of... >> Learn more

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