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Sharp Health News

Why the second dose of COVID-19 vaccine has more kick

Feb. 19, 2021

Player taking penalty kick during soccer match
Jennifer Spengler is a health and wellness writer for Sharp Health News and a marketing specialist with Sharp HealthCare.

Like me, my 22-year-old daughter works in health care. She and I have both been fortunate to receive both doses of a COVID-19 mRNA vaccine. However, we differed in the reactions we each had to the second dose.

With our first dose of the vaccine, we both experienced soreness at the vaccination site. It was nothing that a little acetaminophen couldn't help.

Weeks later, however, the reactions we had to our second dose of the vaccine were far different. Though not unbearable or severe, my reaction was markedly worse than hers.

Both the day I received my second dose and the next day were spent primarily on the couch in front of the TV or in my bed as I slept soundly for hours at a time. Added to my fatigue: a minor headache, body aches and chills.

My daughter, on the other hand, felt nothing more after receiving her second COVID-19 vaccine dose than the arm soreness she had with her first. Is it because she's younger than me? Fitter or healthier than me? While all are true, it might just be that her immune system reacts differently than mine.

A soccer analogy to explain vaccine side effects
This is where another similarity I have with my oldest, as well as my other two daughters, comes in. We all have played soccer, usually in defensive positions. And a soccer analogy can help illustrate why the second dose of the COVID-19 vaccine could lead to more side effects than the first dose.

So, just for kicks, picture this:

Imagine each dose of the COVID-19 vaccine is a soccer player on the opposing team. The first player who goes on attack wears the number 1 on her jersey. The game starts and #1 heads straight toward the goal, uses a little fancy footwork and gets by the defensive line to take a shot.

Coaches are yelling, the other team's fans on the sidelines are cheering and the defense is left feeling a little sore that #1 got the best of them. However, along with feeling sore, they are also now far more determined and ready in case another player heads toward their goal.

In the second half, as another offensive player, let's call her #2, heads down the field, the defense is better prepared and recognizes what is about to happen. The strongest defender marks her immediately, and even some of the midfielders come back to help. The goalie steps forward, prepared to make the save, and yells out to each of her players that it's time to put up a stronger response. The shot is taken, but this time, they know what to expect and how to react.

This is what your body does as it receives each dose of the vaccine. It's shocked into action when #1 hits your line of defense - your immune system - and then offers a more prepared and intense response when #2 is introduced.

What a vaccine reaction really means
According to Dr. Rochelle Walensky, director of the Centers for Disease Control and Prevention (CDC), when you have a reaction to the vaccine, it is an indication that your immune system is kicking in - much like the soccer defenders in the second half - and the vaccine is working. This is true even if a big reaction doesn't occur, like my daughter experienced.

This is because mRNA vaccines use genetic material from the novel coronavirus that causes COVID-19, which gives your cells instructions for how to make copies of the spike protein unique to the virus. Recognizing that the protein should not be there, the body creates protective antibodies - your line of defense - that will remember how to fight the virus in case of future infection.

These antibodies are created after you receive the first dose and are already revved up to react when the second dose is administered. That then primes the immune system to recognize the spike protein if you are later exposed to the actual coronavirus, so it can spring into action quickly and defend your body against it.

What to expect and how to manage vaccine side effects
In addition to side effects being more common after the second dose of the COVID-19 vaccine, the CDC also reports the following information about vaccine side effects:
  • The most common COVID-19 vaccine side effects are pain, swelling and redness in the arm where you got the shot, and chills, tiredness and headache throughout the rest of your body.
  • These side effects usually start within 1 to 2 days of getting the vaccine. They might feel like flu symptoms and might even affect your ability to do daily activities.
  • Side effects should go away in a few days.
It is recommended that you talk to your doctor about taking an over-the-counter medicine, such as ibuprofen or acetaminophen, if you experience pain or discomfort after receiving either dose of the COVID-19 vaccine. You should also drink plenty of fluids and rest, as needed.

To reduce the pain and discomfort in your arm where you got your shot, the CDC suggests you apply a clean, cool, wet washcloth over the area. You can also exercise your arm. This brings up another difference in how we reacted to the vaccine: my younger, fitter daughter chose to go the exercise route, while I chose the cold compress route. Both helped.

However, we don't differ in our belief that getting the vaccine and having mild side effects is far preferable to getting COVID-19. We, like most people, will take sore arms and mild discomfort caused by the vaccine over the risk of severe COVID-19 illness and hospitalization - and even death - any day.

Learn about COVID-19 vaccine distribution, safety and more.

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