Some people see side effects after first dose of COVID-19 vaccine — and this may be why

ATLANTA — We are learning more about how our bodies respond to the COVID-19 vaccine.

While the majority of people have little reaction to their first shot, a select few get pretty sick. And now we may know why.

The reason could be that your body is already familiar with this virus.

For Mike Christensen, 2021 got off to a rocky start with a battle against the coronavirus.

“I started with symptoms on New Year’s Eve. I lost my taste and smell for a day, nausea, diarrhea, just everything — fatigue,” Christensen said. “It really took a lot out of me.”

The Forsyth County resident told Channel 2′s Justin Wilfon that he finally recovered after a couple of weeks. But then just last week, a familiar feeling returned.

“I woke up with a headache, a fever, and I was like that for about 24 hours,” he said.


Just the day before, Christensen had received his first shot of the COVID-19 vaccine.

“The highest my fever got was 102.4. And the highest fever I had when I actually had COVID was 100.5. So it was a higher fever. It felt like I had COVID again,” Christensen said.

According to a recent study done by the school of medicine at Mount Sinai Hospital in New York, this is a common first-shot phenomenon: People who’ve had the virus are more likely to have side effects from the first shot.

Wilfon talked with Dr. Mark Cohen, chief medical officer at Piedmont Hospital, about why it’s happening.

“When your immune system is seeing something that you’ve seen before, you’re all revved up for it,” Cohen said. “So the cell response, the antibody response comes on much faster, much more intense. And with that is all the inflammatory activity that comes along with it.”

But Cohen also warned the study included only a small group of people and said more data needs to be collected before doctors can definitively link a strong first-shot reaction to previous exposure to the virus.

Either way, he said possible shot-induced symptoms shouldn’t stop anyone from getting the vaccine.

“Tylenol, Ibuprofen are very effective at knocking those out in a day, day and a half. It’s very short,” Cohen said.

And even after his strong symptoms, Christensen said it won’t stop him from getting his second shot later this month.

“I would still advise people to get it. It was a minor inconvenience,” Christensen said.

The study also found that people who’ve had the virus developed higher levels of antibodies after the first shot. So you might be suffering a little more than those who’ve not had the virus, but you’ll walk away with a higher level of antibodies.