Europe’s drug regulator says it’s evaluating an assortment of potential side effects following inoculation with leading COVID-19 vaccines, including heart inflammation, facial swelling and a rare nerve-degenerating disorder. Yet in most circumstances, it’s not clear whether the vaccines are to blame.

In AstraZeneca’s case, the European Medicines Agency’s safety committee, known as PRAC for short, said it’s examining reports of Guillain-Barre syndrome (GBS) among people who received the drugmaker’s COVID-19 vaccine, according to a report released on Friday. The agency is tracking the data for all coronavirus shots as part of its routine safety procedures.

GBS syndrome is a rare disorder that causes nerve inflammation and can result in pain, numbness, muscle weakness and difficulty walking. GBS was previously identified by regulators as a potential adverse side effect that required monitoring following AstraZeneca’s jab, the EMA said. The regulator asked AstraZeneca to provide more detailed data and an analysis of all reported GBS cases for its next safety report, which are required on a monthly basis.