Updated: Mar 6, 2021

The flu is caused by a virus, called the influenza virus. When we are infected by the flu virus, our immune system creates cells to fight and remember the virus so we cannot be infected by it again. The Influenza virus, much like the common cold virus, easily mutates and creates numerous strains. This means it changes proteins on itself so it can avoid our immune system from recognizing it and it can then infect us again the next year. This is called “antigenic drift” and is the main reason this vaccine is repeated each year.

How effective is the vaccine?

The identity of the current, circulating strains of the flu is not known until long after the vaccine has been produced for that year. Therefore, the strains that are placed in the vaccine are a guess and are not guaranteed to be the most effective strains for that year’s circulating strains.

If conditions are ideal, the vaccine is about 60% effective(1). This means the individual getting the vaccine is healthy, less than 40 years old, doesn’t smoke, has a proper immune system response to the vaccine and the guessed strains are correct for that year. Research shows that all vaccines are less effective if you are over 40 years old, are overweight, smoke or have a chronic condition(2). The influenza vaccine is only about 30-40% effective in preventing illness among persons 65 years of age and older even when the vaccine strain is the same as the circulating strain(3,4). If you’re older than 70, there are no studies showing that the flu vaccine is effective for this age group, and most deaths from influenza occur in those older than 70 years old(2).

The vaccine alone will not completely protect you against the flu. Other modalities such as good hand washing, good nutrition, proper vitamin D levels and good immune system function are needed.

What's in the Vaccine?

(These are taken from the FDA list of approved products.)

What are the risks of getting the vaccine?

Some of the flu shot’s short-term side effects include:

Low-grade fevers, Headaches, Hoarseness, Sore throat, Coughs, Fatigue, Aches and muscle pains, Soreness, redness or swelling where vaccine was given, Itchiness and toughness where the vaccine was given (for people given an intradermal flu shot) Fainting, Nasal congestion and Nausea (5,6).

Lastly, the flu vaccine may cause damage to your nervous system:

  • Brain and nerve disorders: Flu shots have been linked to brain inflammation and encephalopathy, Acute Disseminated Encephalomyelitis (ADEM), optic neuritis, partial facial paralysis, brachial plexus neuropathy and vasculitis (7).

  • Guillain-Barré Syndrome (GBS): A flu shot can slightly raise your risk for GBS, with estimates being one or two cases per 1 million vaccinations. GBS, which can develop two to four weeks after the vaccination, is an autoimmune disorder that may target your peripheral nervous system, trigger temporary or permanent paralysis and other chronic health problems, or even cause death (5).

Common GBS symptoms to watch out for include muscle weakness, numbness, an unsteady gait, tingling, pain, or facial or limb paralysis.

Research has also found that flu vaccinations may increase children’s risk for illnesses:

  • Flu-related hospitalization — A 2009 Science Daily article details that children between 6 months and 18 years of age who received annual flu shots were more likely to be hospitalized because of flu-related illnesses (8).

  • Pandemic H1N1 or swine flu — Results published in PLoS Med in 2010 showed that people who received the trivalent flu vaccine in the 2008-2009 flu season were more likely to be diagnosed with pandemic H1N1 “swine flu” the year after (9, 10, 11).

  • Respiratory infection — In a 2012 Clinical Infectious Diseases Study article, authors noted that children given the trivalent flu vaccine were four times more likely to be affected with a respiratory infection (12).

If you do experience an adverse reaction to the influenza vaccine, it's important to let your provider know and insist they report serious reactions to VAERS (Vaccine Adverse Event Reporting System).

What are the risks of not getting the vaccine?

If you get the flu, this is generally uncomfortable and can cause typical viral symptoms such as fatigue, fever, cough, sore throat, runny nose/stuffiness, muscle aches, headaches and even vomiting and diarrhea. The flu itself rarely causes complications such as hospitalization or death. It can be dangerous in those with severely compromised lung/heart function and in patients older than 70 years old. These patients have a higher risk for secondary pneumonia, caused by inability to remove fluid from the lungs and subsequent bacterial infection(13).

Wash Your Hands!

Fortunately, there are lots of preventative measures to help reduce the risk of developing a complication such as pneumonia from the influenza virus. You can discuss these with your doctor at any time.

Currently, statistics claim that influenza is the 8th- 9th leading cause of death in North America, but this is because influenza is lumped with pneumonia – even if the pneumonia was caused by something else. In fact, the CDC states that only about 8.5% of all pneumonia deaths are related to influenza, and only 2.1% of all respiratory and circulatory deaths are influenza-related(14).

If you get the flu, this natural infection induces both subtype-specific antibodies and cross protective T-cells to related strains of that virus as well. The result of this is that it offers more global protection from new and emerging strains caused by antigenic drift. It is unlikely that the flu vaccine offers this same benefit(15, 16). Natural immunity to diseases also lasts a lifetime, whereas most vaccine immunity only lasts 1-20 years(17).

What can I do to prevent getting the flu?

If you are exposed to the influenza virus, there is no guarantee you will actually get the flu. Pathogens such as the influenza virus are only a risk to someone who is susceptible, and determining susceptibility includes the following factors:

Influenza Vaccine

Exposure size