Mayuri Bhakta, FNP-BC
Medcor Provider

Why is it recommended that you get a flu vaccination every year? How is the flu vaccine made? And…is the flu “shot” the only vaccination option? Observe National Influenza Vaccination Week by finding out what you didn’t know about the flu vaccine. And if you haven’t yet—be sure to get your flu vaccination!

What is the influenza “flu” vaccine?

Vaccines, also known as vaccinations or immunizations, are given to help your body develop natural defenses against a germ, such as a virus or bacteria. The flu is a viral infection that, among other symptoms, can cause fevers, body aches, cough, congestion, fatigue, and headaches. There are many strains of the flu virus that circulate every year. The flu can cause serious symptoms or secondary infections that can lead to hospitalizations, or even death.

The flu vaccine is a vaccine that helps reduce flu illnesses, doctor’s visits, and missed work due to the flu and can also prevent flu-related hospitalizations.  

Who should get the flu vaccine?

The CDC recommends that all people 6 months of age or older should receive the vaccine every year. It is particularly important for certain people, who are considered high risk, to get vaccinated.

High-risk populations include the following:

  • Children less than 5 years of age, especially those under 2 years of age.
  • People 65 years and older.
  • People with chronic health conditions such as heart disease, diabetes, and chronic lung disease.
  • People with blood, kidney, or liver conditions.
  • People who have a weakened immune system from diseases such as cancer, HIV/AIDS, or other autoimmune disorders.
  • Pregnant women and women who have given birth within the last 2 weeks.
  • Residents of nursing homes or long-term care homes.

You should get the flu vaccine as soon as it is available, and it is best to get the flu vaccine before the end of October.

Why should I get the flu vaccine?

The flu vaccine can prevent you from getting severely sick with the flu, and can help reduce flu illnesses, doctor’s visits, and missed work due to the flu. Getting vaccinated helps others around you, especially people in high-risk populations, from getting sick with the flu. The flu vaccine may also help decrease the risk of serious complications and hospitalizations associated with the flu, and studies have shown that the flu vaccine can greatly reduce a child’s risk from dying from the flu. If you get the flu despite being vaccinated, you may not get as sick as you would if you were not vaccinated.

It is important to get the flu vaccine every year because flu viruses can mutate, meaning that even if you have developed an immunity to one strain of the virus, you may not be immune to its mutated strain. Furthermore, flu vaccine components change every year, and your body’s immunity to a vaccine may decline during the next year.

How effective is the flu vaccine?

Flu vaccine effectiveness varies every flu season. The CDC studies flu prevalence and determines how effective the vaccine is for the current year. Based on recent studies, the flu vaccine can reduce your chance of getting the flu by 40%-60%.

Effectiveness can vary based on how closely the circulating flu strains, during the current year, are matched to the flu strains in that year’s flu vaccine. Influenza A strains can also rapidly mutate which can make the vaccine less effective.

How is the vaccine made?

Because certain influenza strains can mutate rapidly, or new virus strains may emerge, the World Health Organization (WHO) conducts worldwide, year-round surveillance for flu activity. Based on surveillance data collected, WHO makes recommendations as to which strains of flu should be included in the vaccine for the northern and southern hemispheres. Once these recommendations are made, each country makes the decision as to which strains will be included in the current year’s vaccine. In the U.S., the FDA makes the final decision about which three or four virus strains should be included in that year’s flu vaccine.

Vaccines can be manufactured as egg-based, cell-based, or recombinant vaccines.

  • Egg-based flu vaccine production is the most common and can be used to make inactive, injectable vaccines or can be used to make a vaccine which is administered as a nasal spray. This process involves the use of chicken eggs and can take longer to produce vaccines when compared to other methods. This method can be used to make inactive or live attenuated (weakened) influenza vaccine.
  • Cell-based flu vaccine production uses animal cells to make the vaccine, but these vaccines may still contain inactive viruses cultured in eggs.
  • Recombinant flu vaccines are produced without the use of chicken eggs. Recombinant flu vaccines are made from certain genes found in the recommended strains of the flu virus which are combined with other parts of the virus to make the vaccine.

Which flu vaccine should I get?

In the U.S., there are multiple manufacturers of the flu vaccines. Flu vaccines are either trivalent or quadrivalent. Trivalent vaccines contain two Influenza A strains and one Influenza B strain. Quadrivalent vaccines include two Influenza A strains and two Influenza B strains. Talk to your healthcare provider about which type of flu vaccine they recommend for you.

Flu vaccines are available in the following formulations:

  • Both trivalent and quadrivalent vaccines can be administered as an intramuscular vaccination (injection in the muscle) and contains inactive flu virus. Depending on the manufacturer and brand, intramuscular injections can be given to people aged 6 months and older. Most people refer to the intramuscular injection as a regular “flu shot.”
  • Intradermal (under the skin) flu vaccine contains inactive quadrivalent flu virus and is given using a smaller needle than a regular flu shot. This has been approved for use in people aged 18 – 64 years of age.
  • Flu vaccine by jet injector uses a jet injector device to deliver a trivalent or quadrivalent vaccine instead of using needles. This has been approved for people aged 18 – 64 years. This method has a higher rate of side effects at the vaccination site.
  • Nasal spray formulation is a quadrivalent live attenuated influenza vaccine, which means it contains weakened flu virus. The nasal spray vaccine is approved for use in people aged 2 – 49 years old. It is not approved for people in a high-risk population.
  • A high-dosed intramuscular vaccine is often recommended for people aged 65 years and older.  

It is important to talk to your healthcare provider about which flu vaccine is the best option for you.

What if I have an egg or thimerosal allergy?

Before getting any vaccinations, it is important to talk to your healthcare provider to get recommendations specific to your allergens.

The CDC currently recommends that even people who are allergic to eggs should receive the flu vaccine. If you have a severe egg allergy, you should be vaccinated in a medical setting such as a clinic or hospital.

Thimerosal is a preservative used in some types of vaccines. If you have a thimerosal allergy, you will need to talk to your healthcare provider about getting a flu vaccine that does not contain thimerosal.

If you have had a severe allergic reaction to the flu vaccine in the past, you should not receive a flu vaccine.

What kind of side effects does the flu vaccine cause?

Getting the flu vaccine will not cause you to get the flu. Typical side effects from flu vaccines are mild and short-lived. The intramuscular, intradermal, and jet injector administered flu shots contain inactive viruses. Side effects from the inactive flu viruses can cause slightly different side effects than the nasal spray, which contains weakened viruses.

Side effects from the inactive flu virus vaccine include:

  • Low grade fever
  • Headache
  • Muscle and body aches
  • Nausea
  • Redness, swelling, or soreness at the injection site (more common with flu vaccine with jet injector)
  • Feeling tired

Side effects from the nasal spray vaccine with weakened flu viruses include:

  • Runny nose
  • Wheezing
  • Cough
  • Muscle and body aches
  • Sore throat
  • Headache
  • Low grade fever
  • Feeling tired
  • Nausea and vomiting

Be sure to get your flu vaccination so that you can stay healthy this flu season!

This article is not intended to diagnose or treat any condition or to give medical advice. Always consult your healthcare provider for healthcare instructions. External links are provided as references and do not indicate an endorsement by Medcor. External links are subject to other sites’ terms of use and privacy policies.

1 Centers for Disease Control and Prevention, “Flu Vaccine and People with Egg Allergies,”

2 Centers for Disease Control and Prevention, “How Flu Vaccine Effectiveness and Efficacy is Measured,”

3 Centers for Disease Control and Prevention, “How Influenza (Flu) Vaccines Are Made,”

4 Centers for Disease Control and Prevention, “Key Facts About Seasonal Flu Vaccine,”

5 Centers for Disease Control and Prevention, “People At High Risk For Flu Complications,”

6 Centers for Disease Control and Prevention, “Selecting Viruses for the Seasonal Influenza Vaccine,”

7 Centers for Disease Control and Prevention, “Vaccine Effectiveness: How Well Do the Flu Vaccines Work?,”

8 Patricia L Hibberd, “Seasonal influenza vaccination in adults,” UptoDate, updated September 19, 2019.