A new vaccine safety study has uncovered new side effects to many COVID vaccines. The effects, which are extremely rare, were discovered during the largest vaccine safety study to date.

The side effects were discovered in a study conducted by the Global Vaccine Data Network , a research division of the World Health Organization. According to Science Alert, the study looked at 99 million vaccinated individuals who had received vaccines made by producers like Pfizer, Moderna, and AstraZeneca, among other manufacturers. The study focused on people in countries located in six continents across the world. The study compared rates of 13 different conditions in patients after they had received their vaccine to the rates of those conditions in the general population.

Researchers revealed that the vaccines had relations to two rare conditions. The Guardian states that the study confirmed highly accurate connections between the mRNA COVID vaccine, produced by Pfizer and Moderna, as well as vaccines produced by AstraZeneca to the rare conditions. Myocarditis (inflammation of the heart) and pericarditis (swelling of the sac around the heart) were found in the mRNA vaccine. More severe conditions were found in the AstraZeneca vaccine, which include Guillain-Barré syndrome, which causes the nerves to be attacked by the immune system. The AstraZeneca vaccine has also been linked with cerebral venous sinus thrombosis (a blood clot in the brain) and acute disseminated encephalomyelitis (inflammation and swelling in the brain and spinal cord).

While the side effects are serious, the chance of experiencing them is low, as Forbes wrote. Some highlighted increases include a 6.1-fold increase in myocarditis from the second dose of the Moderna mRNA vaccine. Cases of pericarditis had a 6.9-fold increase as a result of the third dose of the AstraZeneca vaccine. There is a 2.5-times greater risk of developing Guillain-Barré syndrome from the AstraZeneca vaccine along with a 3.2-times greater risk of developing blood clots from the same vaccine. There is a 3.8-times greater risk of getting acute disseminated encephalomyelitis from the Moderna vaccine, and a 2.2-fold increase in the AstraZeneca vaccine.

When choosing to get vaccinated, it is important to weigh the benefits and risks of the vaccine. Information like this makes it easier to make the right choice.