Photo: aijiro (Shutterstock) Some people who got the Johnson & Johnson/Janssen COVID-19 vaccine (the one-dose vaccine) have developed a condition known as Guillain-Barré syndrome . It’s happened often enough that the FDA has asked them to add a note about this to the patient fact sheet, but it’s still not considered to change the risk/benefit balance of getting your shot. (All the COVID vaccines are much safer than getting actual COVID.) What is Guillain-Barré syndrome? First, because it’s not obvious: The first word is pronounced “GEE-yawn” and the second rhymes with “hooray.” People sometimes just call it GBS. GBS isn’t new: it’s already known to happen to about 1 in 100,000 people each year, and 60-80% of cases follow a bacterial or viral illness, like the flu or food poisoning, according to the GBS-CIDP Foundation International . GBS is also a known and rare side effect of the flu vaccine, although you’re more likely to get GBS from the actual flu than from the flu vaccine . In GBS, the immune system attacks the insulation on our nerve cells. (If you think of the rubber coating around an electrical wire, each of our long skinny nerve cells is like that wire, and there are cells full of an insulating substance called myelin that surround it.) As a result, people may have weakness or numbness in the legs, or nerve problems in other areas of the body that could include trouble breathing or trouble moving the muscles of the face. […]