What you should know before saying yes to the flu shot.

What you should know before saying yes to the flu shot.

The flu shot is a common offering in doctors’ offices everywhere. If you are wondering whether to get a flu shot this season, read on to find out more:

According to the CDC,

recent studies show that flu vaccination reduces the risk of flu illness by between 40% and 60% among the overall population during seasons when most circulating flu viruses are well-matched to the flu vaccines (1).

Potentially, with the flu shot, we could be half as likely to get the flu. That’s great, right? Wait, but there is a major qualifier in that statement. Let’s look at it more carefully.

The effectiveness of the flu vaccine very much depends on how “well-matched” the vaccine is to the flu virus(es) of that season. And producing a “well-matched” vaccine is more difficult than it sounds.

The flu vaccine only protects against 3 or 4 strains of the influenza virus each year (2). Influenza A and B are the primary types responsible for flu epidemics in humans. However, within the A type alone, there are 16 different types of hemagglutinin (the H in H1N1, for example) and 9 different types of neuraminidases (the N in H1N1). Therefore, there are potentially 144 different strains of influenza A viruses. Furthermore, because the hemagglutinin gene mutates all the time, there are many variants of the same subtype virus.

Another point to consider is that it takes at least 6 months to produce large quantities of the influenza vaccine (3). This means that as early as January of this year, vaccine manufacturers were already starting to grow the viruses to produce the vaccine for the following season. This is a problem because while the CDC and other WHO centers do their best to study up on viral trends and new, emerging strains, the predominant viral strain(s) responsible for the flu each season is usually not identified until well into the season, when it is too late to make a vaccine against it.

Finally, not all influenza viruses lend themselves to the vaccine manufacturing process. Today the majority of influenza viruses used to make the vaccine are grown in chicken eggs (3). However, the predominant influenza strain of the 2017 - 2018 season was the H3N2 virus, which does not grow well in eggs. The CDC itself acknowledges this as a key reason that the vaccine is less effective against this subtype of influenza A virus (4).

According to the CDC,

During years when the flu vaccine is not well matched to circulating influenza viruses, it is possible that little or no benefit from flu vaccination may be observed (1).

Let’s say though, you want to take your chances that there is a “vaccine match” this year. Let’s consider what the known side effects are.

As many people who have received the flu vaccine know, the most common side effects are soreness, redness, tenderness or swelling where the shot was given, as well as low-grade fever, headache and muscle aches, not to mention the many ingredients that you may not want to have in your body (5). While the vaccine does not actually give you the flu, it can cause symptoms that are quite similar to those of the flu. This is because, flu viruses, while inactivated or only partially utilized, are being injected or inhaled.

Another side effect of the vaccine that not many people think about is that vaccinnation leads to several days of viral shedding, which although is less contagious, can still be spread to susceptible individuals, such as the elderly and young children.

Furthermore, it takes the immune system 2 weeks following vaccination to develop the antibodies against the strains of influenza you were vaccinated against. In this 2-week post-vaccination period, in addition to being somewhat contagious to those around you, you could still catch the flu despite having just received the vaccine.

This article is NOT a blanket recommendation to avoid the flu shot. The flu can be a serious illness and in the U.S., results in:

  • 9.2 - 35.6 million cases each year

  • Tens of thousands of deaths: 12,000 - 56,000 or 0.3% to 0.61%

  • Many more hospitalizations due to complications 140,000 - 710,000 or 0.39% - 7.7% (6).

In some people, the flu shot may be instrumental in helping reduce the severity of illness. If you are over the age of 65, a child, a pregnant woman, anyone with a compromised immune system or in close/frequent contact with these populations, we recommend speaking with one of us or your doctor to weigh the risks and benefits of a flu shot.

Stay tuned for our next post on some whole-body ways to strengthen your immune system and stay healthy throughout the season.


(1) CDC: https://www.cdc.gov/flu/about/qa/vaccineeffect.htm

(2) WebMD: https://www.webmd.com/vaccines/how-effective-is-flu-vaccine#1

(3) CDC: https://www.cdc.gov/flu/about/season/vaccine-selection.htm

(4) CDC: https://www.cdc.gov/flu/about/qa/misconceptions.htm

(5) CDC: https://www.cdc.gov/flu/about/disease/burden.htm

5 Ways to Stay Strong This Season

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