The flu is a contagious respiratory illness that’s caused by influenza viruses. While some people experience mild symptoms, others can become seriously ill.

Each year, a seasonal flu vaccine is available to help protect you from becoming sick with the flu. There are different types of flu vaccines that you can get, one of which is the flu shot.

As with any vaccine, it’s possible that you’ll experience mild side effects after receiving the flu shot. One of these is a sore arm, which we’ll discuss in more detail in this article.

Having a sore arm after getting the flu shot is very normal. The soreness or discomfort typically goes away after a few days.

Why is your arm sore?

The flu shot introduces influenza virus components into your body. This can be in the form of an inactivated (“dead”) virus or single viral proteins.

The goal is for your immune system to make antibodies to fight off these viral components. These antibodies can then protect you against an actual influenza infection.

While the flu shot cannot cause you to become sick with the flu, your immune system still recognizes what’s been injected into you as foreign.

As a result, it produces an immune response, which leads to the soreness or swelling that occurs near the injection site.

Why is the shot given in your arm?

Muscle tissue, like that found in your arm, has a high concentration of blood vessels. This allows the cells of your immune system to effectively access and process the contents of the vaccine.

Additionally, a 2000 research review showed that serious reactions to vaccines given into muscle tissue are rare.

In addition to a sore arm, other common side effects of the flu shot may include:

These side effects are typically mild and usually go away after a few days.

Like other types of injections, it’s possible that the flu shot may cause fainting, especially if you have a fear of needles and injections. This is why it’s typically given when you’re seated or lying down.

Serious side effects

According to the U.S. Department of Health and Human Services, serious side effects from the flu shot are very rare. When they do occur, they can include:

If you have a sore arm after getting the flu shot, you may want to try the following to help ease your symptoms.

  • Rest your arm. Moving your arm around during your daily activities may further aggravate the area. Because of this, it may be helpful to get the flu shot in your nondominant arm.
  • Try over-the-counter (OTC) medications. Taking an OTC medication may help relieve pain and swelling at the injection site. Some examples include:
  • Use cold therapy. Using an ice pack or a cool compress at the injection site can also reduce pain and swelling.

In addition to the flu shot, a nasal spray vaccine is also available. You may see this vaccine referred to as FluMist or the live attenuated influenza vaccine (LAIV).

This vaccine is sprayed into your nose. Unlike the flu shot, it contains active (“live”) influenza viruses. However, these vaccine viruses have been weakened so they won’t cause an infection.

Like the flu shot, the nasal spray has some potential side effects. These can be different in adults and children and can include:

Additionally, younger children may experience:

The nasal spray vaccine is approved for individuals ages 2 to 49. It’s not recommended for certain groups, such as pregnant people and those with a weakened immune system.

If you’re interested in receiving the nasal spray vaccine, talk with your doctor about whether it’s a safe option for you.

Is the nasal spray as effective as the flu shot?

In the past, the Centers for Disease Control and Prevention (CDC) recommended against getting the nasal spray vaccine.

The reason for this was because studies in children found that it was less effective than the flu shot for protecting against the 2009 H1N1 pandemic influenza strains.

However, there have been recent advances in the production of the nasal spray vaccine.

Since the 2018 to 2019 flu season, the CDC has recommended the nasal spray vaccine because data suggest that it’s now as effective as the flu shot in children.

The CDC currently recommends that all people 6 months and older be vaccinated for flu. One type of vaccine isn’t recommended over another, so you can choose the flu shot or the nasal spray.

Receiving a flu shot is especially crucial in groups that are at risk of serious illness or complications from the flu. This includes:

  • adults ages 65 and older
  • children younger than 5 years old, particularly those under 2 years old
  • pregnant people
  • people with underlying health conditions, such as asthma, diabetes, or cancer
  • those with weakened immune systems
  • individuals living in a nursing home or long-term care facility

Getting your flu shot is also particularly important in light of COVID-19. Both the flu and COVID-19 have similar symptoms and will circulate within communities this winter.

While the flu vaccine won’t protect you from COVID-19, it can help prevent you from getting the flu.

In addition to keeping you out of the doctor’s office, this can also conserve medical resources for those that have COVID-19 or other health conditions.

Is there anyone that shouldn’t get the flu shot?

Speak with your doctor before receiving a flu shot if any of the following are true:

  • you’re currently ill
  • you’ve had a previous severe allergic reaction to the flu shot or any of its ingredients
  • you’ve had Guillain-Barre syndrome

A flu shot should help to protect you for the duration of the current flu season. However, you’ll need to get another flu shot next fall.

You may be wondering why you need to get a flu shot every year. There are a couple of reasons for this. One is related to the virus itself while another has to do with your level of immunity.

Influenza viruses are continually evolving throughout the year. Because of this, last year’s vaccine may not be a good match for the viruses that are prevalent this flu season.

The flu vaccine protects against the strains of influenza that research predicts will be the most prevalent in the upcoming flu season.

Your vaccine will typically include four strains (quadrivalent), but may sometimes include three (trivalent).

Additionally, a 2019 research review showed that the immunity provided by the flu shot decreases quickly over time.

This is why you likely won’t have enough immunity from this year’s shot to protect you into the next flu season.

What happens if you still get the flu?

It’s possible that you can still get the flu, even if you received your flu shot. However, your illness likely won’t be as severe as it would be if you hadn’t been vaccinated.

A 2017 research review investigated the effect of the flu vaccination on illness severity in adults. It found that vaccination was associated with lower influenza-related hospital stays, ICU admissions, and deaths.

A sore arm is a very common side effect of the flu shot. It typically goes away after a few days. In the meantime, you can use OTC pain medications or an ice pack to ease pain and swelling at the injection site.

If you don’t want to get a shot, there are other vaccination options available to you. The nasal spray vaccine is sprayed into your nose. Like the flu shot, it also can cause mild side effects.

The CDC recommends that everyone ages 6 months and older receive the flu vaccine.

This is particularly important for those at risk of serious flu illness. While it’s best to get the vaccine in the early fall, it can be beneficial at any point in the flu season.