New research suggests COVID-19 vaccines could provide benefits aside from protecting against the coronavirus: they also seem to cut the risk of heart failure and blood clots linked to SARS-CoV-2.

The study, put together by an international team of researchers, involves an analysis of data covering 10.17 million vaccinated people and 10.39 million unvaccinated people in the UK, Spain, and Estonia.

After accounting for factors including age, sex, and pre-existing conditions, those who had been vaccinated were shown to have a significantly reduced risk of cardiac and clot-related complications after having COVID-19, for up to a year.

"Our findings probably reflect the fact that the vaccines are effective in reducing infection, and minimize the risk of severe COVID-19," says data scientist Núria Mercadé-Besora from the University of Oxford in the UK.

"These results could encourage COVID-19 vaccination among hesitant people who are worried about the potential risk of vaccine side effects."

Compared with people who hadn't been vaccinated, COVID-19 vaccination was linked to a 78 percent reduced risk of blood clots in the veins, a 47 percent reduced risk of blood clots in the arteries, and a 55 percent reduced risk of heart failure in the first 30 days post-infection.

While those risk reductions dropped as time went on, they were still at 50 percent, 38 percent, and 48 percent respectively at 181-365 days. While previous studies have come up with similar findings, this is one of the most comprehensive investigations to date in terms of the number of people studied and the length of time they were monitored for.

Blood clots, which can cause strokes, and heart failure are known to be far more common in the wake of a COVID-19 infection. While the research doesn't establish a clear cause and effect, it does suggest that being vaccinated against the disease also lessens the risk of further complications.

The team acknowledges it's a complicated picture, though COVID-19 vaccines have been shown to be mostly safe and effective and the benefits outweigh potential disadvantages. However, they'd like to see more research done to look at the protective effects of COVID-19 vaccines in more detail.

"The protective effects of vaccination are consistent with known reductions in disease severity, but we need to do more research to understand the effects of a booster vaccination in different populations," says Mercadé-Besora.

The research has been published in Heart.