Why the COVID-19 Vaccine Can Make You Feel Awful

What you can do to relieve the post-vaccine symptoms of fatigue, arm pain and headaches

Got your COVID-19 vaccine then you feel headachy, crummy and sore? Congrats, your body is doing what it’s supposed to do.

“The reactions, for the most part, are because your body is making a response, giving you immune protection,” says Dr. Dennis Cunningham, system medical director of Infection Control and Prevention at Henry Ford Health System. “When your white blood cell counts are reacting to a vaccine, your white blood cells put out interferon, that’s a protein that makes us feel a little lousy, can make us feel achy and just feeling crummy.”

But, if you have no symptoms, don’t worry. Your body is still giving you protection, he says.

As the Moderna, Pfizer and Johnson & Johnson vaccines reach more people — with Pfizer expected to be approved by the FDA for kids 12-15 as early as next week — more people are sharing their body’s reactions to the shots with work colleagues, on social media and to anyone who will listen.

And social media would have you believe it’s hit or miss if you’ll have symptoms after your vaccine. In reality, Cunningham says the younger you are, the more likely you are to have a reaction, especially if you are under 55. In addition, people who have had COVID (even those who didn’t know they had it) and get the vaccine tend to get a littler sicker, he says.

“Most people are going to have some mild symptoms,” he says. That includes injection site pain, achiness or tired and a headache.

When Cunningham received his second dose, he says he did feel crummy for a day, achy, tired and chilled. “I would gladly take that less than 24 hours of symptoms to avoid getting COVID.”

What you can do

If you do get symptoms, Cunningham says it tends to be short-acting, less than two days, and usually less than one day. “It passes and you are going to get back to normal and fortunately you are going to have some protection against coronavirus,” he says.

That said, here are the most common symptoms and his recommendations:

1. Headache, overall achiness, arm pain

Once symptoms start, take Tylenol, Advil or some other over-the-counter medicine for relief, he says. Just follow the instructions on the box.

However, Cunningham doesn’t recommend taking anything before getting the vaccine. In small studies, some data has shown, at least in kids, that the body doesn’t respond as well to vaccines. Waiting until symptoms appear shows no diminished response to a vaccine. So, his best advice: Wait until you feel crummy, then take something.

2. Lightheadedness

You’ll hear lots of advice from people suggesting you drink lots and lots of water the day before, day of and day after your vaccine. Cunningham says while it’s always important to drink enough to be hydrated, he doesn’t know how important it is to drink a lot of fluid.

However, he has noticed people getting lightheaded after their shots. “I like people to come in with the tank filled up,” he says, meaning don’t arrive for your vaccine on an empty stomach.

3. Tiredness

Rest. If you don’t feel well, rest when you can, Cunningham says. But he says the vast majority of people, 98% who classify their symptoms as mild or moderate, are still going to be able to go to work, go to school and do their daily activities.

4. Sore or stiff arm

This is the most typical reaction, he says. It is simply the body’s response to the vaccine since it is injected into the upper arm.

If your arm hurts, he says some people like to put on a heating pad or run hot water in the shower over it. “Really what you need is pain relievers and time,” he says.

Since the symptoms are similar in all three of the vaccines, if you are wondering what vaccine is best, Cunningham has this simple advice: “The right vaccine is whichever one you can get,” he says, adding that all three available vaccines are proving to be very effective, safe vaccines.

You are considered fully immunized two weeks after the second dose of both Moderna and Pfizer and two weeks after the single shot of Johnson & Johnson. And if you happen to get COVID after your vaccines, Cunningham says you likely won’t even have to go to the doctor or ER because symptoms will be so mild.

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Metro Parent Editorial Team
Metro Parent Editorial Team
Since 1986, the Metro Parent editorial team is trained to be the go-to source for metro Detroit families, offering a rich blend of expert advice, compelling stories, and the top local activities for kids. Renowned for their award-winning content, the team of editors and writers are dedicated to enriching family life by connecting parents with the finest resources and experiences our community has to offer.


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