This Vaccine Reaction Means You May Have Already Had COVID, Study Says

Research found this reaction is more common among those who have been previously infected.

Over the last year, we've seen how differently COVID-19 can affect people who contract the virus. While some experience debilitating symptoms when infected, others have no symptoms at all. In fact, there is a chance that you could have been infected with the coronavirus and still not even know it. But there are some commonalities that can be seen in all patients who have recovered from COVID, whether they were symptomatic or asymptomatic. In fact, new research has found that one vaccine reaction in particular could indicate that you have already had COVID.

RELATED: Doing This After Your Vaccine Can Make Side Effects Worse, Doctors Say.

Resting heart rate increases for some people as a reaction to the COVID vaccine.

Senior tired man checking pulse after workout. Old man measuring heart rate pulse on his neck and looking sport watch. Aged man times the pulsations at park.

Researchers from the Scripps Research Translational Institute in California reported on physiological responses to the COVID vaccines, publishing an early version of their study May 4 on medRxiv. The researchers collected data from more than 4,000 Americans using a smartphone-based app that reports on physiological activities from smartwatches, and found that some people experience increased heart rate as a reaction to the vaccine. According to the study, the researchers found that some people's resting heart rate increased up to an additional 1.5 beats per minute (BPM) after receiving a dose of either the Pfizer or Moderna vaccine.

Vaccine recipients who had been infected with COVID experienced higher heart rates.

A female doctor wearing gloves and using a syringe with cotton to vaccinate a male patient, covid-19 or coronavirus vaccine.

The researchers found that those who had previously been infected with COVID had higher heart rates than those who had not been infected. However, this was only the case for the first dose. According to the study, people who had been previously infected experienced heart rate increases of more than 1.5 BPM after the first dose between the first and fifth day after vaccination. However, those who had not been previously infected only experienced an increase of less than 0.5 BPM in the same time frame after the first dose. For the second dose, both those previously infected and those who hadn't had COVID saw an increase of more than 1.5 BPM between the first and fifth day after vaccination.

"We identified a rapid rise in heart rate the day after vaccination, and one that was more robust after the second dose, unless the participant had prior COVID-19 infection," the researchers stated in the study.

RELATED: This Vaccine Side Effect Could Mean You Already Had COVID, New Study Says.

Those who got the Moderna vaccine experienced the most significant changes in heart rates.

Moderna vaccine

While this vaccine response was reported in participants who received both the Pfizer and Moderna vaccines, the researchers found more significant heart rate changes in those who got Moderna after both doses. According to the study, Moderna participants experienced heart rate increases of more than 0.5 BPM after the first dose, while Pfizer recipients experienced increases of less than 0.5 BPM. For the second dose, both increases were higher, but Moderna participants experienced an average increase of more than 2 BPM while Pfizer participants saw an average increase of more than 1 BPM.

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Heart rate levels may not return to normal for days after your shot.

woman checks her heart rate and other activity levels on her smart watch.

According to the study, most people vaccinated with Moderna and Pfizer experienced an increase in their resting heart rate in the two days after their vaccination, with 70 percent experiencing it after the first dose and 76 percent experiencing it after the second. The researchers found that changes in resting heart rate peaked on the second day after vaccination, but still lasted several days after that. For the first dose, participants' heart rates did not return to normal until the fourth day after they received their shot. And for the second vaccine dose, their heart rates did not return to normal until the sixth day after their shot.

RELATED: Doctors Are Warning You to "Be Prepared" for This After Your Second Dose.

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