Abigail Klein Leichman
January 2, 2023

In a first-of-its-kind study, physiological data recorded by smartwatches was used to examine the safety of Covid-19 booster vaccines.

Led by PhD student Matan Yechezkel, researchers at Tel Aviv University equipped 4,698 Israelis with smartwatches to monitor physiological parameters — such as heart rate, variation in heart activity, quality of sleep, and number of daily steps taken — over two years.

All study participants were asked to fill out daily questionnaires about their health status via a specially developed app.

More than 2,000 of the participants received the booster dose of the Pfizer Covid-19 vaccine during the study period, allowing the researchers to objectively compare measures before and after that dose.

In addition, the researchers analyzed the medical files of 250,000 randomly chosen members of the Maccabi Health Services HMO – anonymously, in collaboration with Maccabi’s KSM Research & Innovation Center – to detect potential unusual events connected with receipt of the vaccine booster. They evaluated the records from 42 days before receiving the vaccine to 42 days afterward.

Safety from 3 perspectives

The researchers were therefore able to evaluate the safety of the vaccines from three perspectives: subjectively (what the participant reports), objectively (what the watch detects) and clinically (what the physician diagnoses).

“We saw clear and significant changes after administration of the vaccine, such as an increase in heart rate compared to the pulse rate measured before vaccination,” said study supervisor Prof. Dan Yamin, head of the TAU Laboratory for Epidemic Research.

“And then we saw a return to the participant’s baseline, i.e., the pulse levels after vaccination returned to their previous levels after six days,” Yamin said.

“Hence, our study confirms the safety of the vaccine. The research also allowed us to compare subjective and objective indicators and medical diagnosis of the same participant who received the first booster and a few months later the second booster,” he added.

“We found no difference in the physiological response recorded by the smartwatches or that reported by the participant in the app.”

25 side effects

Based on medical literature that has reported 25 unusual side effects attributed to the mRNA Covid vaccine, the researchers were on the lookout for rare cases of inflammation of the heart muscle (myocarditis) and pericarditis.

They report that they found no increase in serious incidents of any kind associated with the vaccination.

“If the watch reports any minor changes in the muscles, and the participant reports only significant changes he feels, the medical file tells us about unusual events diagnosed by the doctors as well as hospitalizations that may be related to vaccinations, with an emphasis on cardiac events,” Yamin explained.

“We did a comprehensive analysis of all those 25 unusual side effects, and we did not see an increase in their incidence among those receiving the booster. We found the vaccine to be safe to use.”

Yamin added: “The smartwatch sensors ‘felt’ that the vaccine was safe, the vaccinee himself reported that the vaccine was safe, and finally, the doctors determined that the vaccine was safe. The results of the study have far-reaching implications regarding objective testing of vaccine safety in the future.”

Smartwatches more precise

The researchers said their most surprising finding was that the watches were more sensitive than the people they were monitoring.

For example, many participants reported symptoms such as fatigue and headache for two or three days after receiving the vaccine. However, the watches were still detecting distinct changes in heart rate for several more days after the person reported feeling back to normal.

“There were also vaccinated participants who did not report any side effects at all and yet definitely experienced physiological changes, based on data from their smartwatches,” said Yamin.

Published in Lancet Respiratory Medicine, the research study was done in collaboration with Prof. Erez Shmueli, head of TAU’s Big Data Laboratory, and with Tal Patalon and Sivan Gazit of KSM Research & Innovation Center, as well as Amichai Painsky and Merav Mofaz from Tel Aviv University.

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