COVID-19 vaccines did not cause an increased risk of adverse events such as heart attack, stroke, cardiac arrest, myocarditis, pericarditis, and deep vein thrombosis, according to a study.

The research, published in the journal Vaccines, monitored the entire population of the Italian province of Pescara for 18 months, from January 2021 to July 2022.

The team led by researchers from the University of Bologna in Italy collected inhabitants' health data and analysed the frequency of a number of serious diseases such as cardiovascular disease, pulmonary embolism and thrombosis.

Pulmonary embolism is a blood clot that blocks and stops blood flow to an artery in the lung while thrombosis occurs when blood clots block veins or arteries.

The study showed that none of the diseases examined was found to be more frequent among the vaccinated than among the non-vaccinated.

"The results obtained clearly show that there was no increased risk of serious diseases among the vaccinated," said Lamberto Manzoli, a professor at the University of Bologna.

"There were isolated adverse cases, but the safety profile of the vaccines used during the pandemic was confirmed: it is now important to continue the follow-up over a longer period," Manzoli said.

The study is currently the only one in the world that monitored the population for more than a year, taking into account numerous factors including age, gender and clinical risk of the participants.

More specifically, the results obtained show that both deaths registered and the occurrence of the diseases examined were less frequent among vaccinated persons, regardless of gender, age and clinical risk profile.

The analysis also confirmed that vaccinated persons who contracted COVID-19 were more protected against the coronavirus than those who recovered after contracting the disease but were not vaccinated.

A higher incidence of the diseases considered was found among those who had not contracted COVID-19 and had only one or two doses of the vaccine, compared to those who had three or more doses, the researchers said.

"This counterintuitive finding is due to an epidemiological bias caused by the restrictions implemented during the emergency," Manzoli.

The data gathered show that 83.2 per cent of the vaccinated population who did not contract COVID-19 received at least three doses of vaccine.

"Those who received only one or two doses did not complete the vaccination cycle either because they died or because they were deterred by the onset of a disease," the scientist added.