By Chris Tye

CHICAGO (CBS) — There are three COVID-19 vaccine makers and millions of drug takers in Illinois, and while most are just feeling fatigued, there are more than a dozen symptoms doctors are seeing after patients take the shot.

So, the simple question is: Which ones are ok and which ones are cause for concern?

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People who spoke with CBS 2’s Chris Tye reported feeling aches in the arm the following day, fully body chills and “not bad at all.”

So CBS 2 asked three big questions to Dr. Michelle Prickett, an associate professor of pulmonary critical care at Northwestern Medicine.

Is there such a thing as how we should feel after shots one or two? 

“The most common side effect after both shots is fatigue,” she said. “People just feel tired. Your immune system is really cranking up, so most people want to go take a nap.”

Other than fatigue, there are other symptoms that should not cause alarm: fever, pain and swelling at the injection spot, mild headache, muscle pain, nausea and vomiting.

Prickett said symptoms that are of concern are: shortness of breath, blood clots, red bumps on the skin, severe headaches or sustained migraines, slurred speech, tongue or lip swelling and passing out within 30 minutes of the injection.

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If these symptoms are severe, like passing out or continued numbness, patients should go to an emergency room. If it’s more mild like skin discoloration or shortness of breath, they should call their physician, Prickett said.

Can we forecast who is going to feel these things more than others?

“The data shows younger people will have more response, and those who have had a prior infection may have more of a response,” she said.

And with the Johnson & Johnson vaccine currently sidelined, the third big question is about the two big brands.

There are concerns that Modern gives more side effects than Pfizer. Is there any science behind those theories? 

“Pfizer and Moderna are almost the exact same vaccine,” Prickett said. “There can be small difference3s. There has been discussion of redness on the site of injection for Modern that’s been more witnessed than Pfizer.”

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It is also common that the second shot comes with more pain than the first. That is expected.