A team of researchers at Tel Aviv University has published a study with “far-reaching implications” for studies on vaccine safety, the scientists said. The study relied in part on data obtained using thousands of smartwatches to affirm the safety of Covid-19 vaccines.

The large-scale two-year clinical study comes at a time when fewer eligible people in the U.S. are opting to get a Covid-19 booster shot. In California, 72.5 percent of eligible residents received their primary Covid-19 vaccine series, but only 60.7 percent of Californians got a booster following their two initial doses. And just 21.4 percent of eligible Californians have received the most up-to-date, bivalent Covid-19 booster shot, according to statewide vaccination data reported through CA.gov.

The researchers, who work in the fields of epidemiology and “big data” analytics at Tel Aviv University, sought to determine the safety of the Covid-19 vaccine and boosters, using health metrics collected from smartwatches in addition to medical health records and subjective participant responses.

Researchers equipped 4,698 Israelis with smartwatches to monitor their vitals and health metrics, such as heart rate, variation in heat activity, quality of sleep and the number of steps taken daily. Participants also completed daily questionnaires where they could report any noticeable vaccine side effects or changes to their health. Additionally, with their permission researchers analyzed the health records of 250,000 randomly selected members of Maccabi Healthcare Services, one of four Health Maintenance Organizations active in Israel.

Participants in the main study were divided into two groups: 2,038 of the participants received the booster dose of the coronavirus vaccine, and 2,660 did not.

Our study confirms the safety of the vaccine.

Using medical files, the smartwatch data, and questionnaire responses, researchers compared the condition of the vaccinated patients with their baseline health 42 days before and 42 days after receiving the vaccine.

“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 Dan Yamin, Head of the Laboratory for Epidemic Research at Tel Aviv University. “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,” he added. “Hence, our study confirms the safety of the vaccine.”

Researchers also found no difference in the physiological response recorded by the smartwatches or reported by participants after they received a second booster a few months later.

Researchers checked the frequency of rare unusual side effects, such as inflammation of the heart muscle, or pericarditis (swelling of the tissue surrounding the heart), by studying the health records of the randomly selected Maccabi Healthcare members, and found no increase that could be associated with the vaccine.

The research was carried out by a PhD student as well as several professors within TAU’s Fleischman Faculty of Engineering, in collaboration with Kahn Sagol Maccabi Research and Innovation Center (the research and innovation institute of Maccabi Healthcare Services). The results of the research were published on November 18, 2022, in The Lancet Respiratory Medicine.

One of the study’s most surprising findings was that smartwatches measured distinct changes in heart rate several days longer than participants reported experiencing side effects such as headaches and fatigue. Some participants who received the Covid-19 vaccine did not report experiencing any side effects, even though their smartwatches detected physiological changes.

“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,” Yamin said. “The results of the study have far-reaching implications regarding objective testing of vaccine safety in the future.”