(NewsNation) — A new study discovered possible links between COVID-19 vaccines and possible neurological, blood and heart-related conditions.

The new study, published in the journal Vaccine, is the largest of its kind since the pandemic began and could reignite the debate over the risks and benefits of the vaccine.

Over the past three years, more than 13.5 billion doses of COVID-19 vaccines have been administered around the world. The World Health Organization recently announced vaccination has saved at least 1.5 million lives in Europe alone.

The study links vaccines to slight increases in neurological, blood and heart-related conditions such as myocarditis, pericarditis and Guillain-Barré syndrome.

Researchers stressed that an association between the vaccine and adverse side effects does not prove the vaccine caused them and that side effects were rare.

Of the more than 99 million people studied, researchers observed 190 cases of Guillain-Barré Syndrome, which is typically developed after a viral infection but has also been linked to vaccines in rare cases, and 69 cases of hematological conditions.

COVID-19 itself can also cause side effects that affect the heart, including myocarditis.

Those who have experienced side effects include 24-year-old George Watts Jr. of New York, a healthy college student who died of vaccine-related myocarditis two years ago. The condition is listed as a possible side effect of the Pfizer vaccine.

There has been partisan fighting for years, with Republicans objecting to vaccine mandates and saying the vaccine was rushed to market, while Democrats pushed for mandates in the name of public health for Americans overall.

Since the pandemic began in March 2020, nearly seven million people have died globally from COVID-19, including more than one million Americans.