Johnson & Johnson vaccine recipients have greater risk of Guillain-Barré syndrome, study finds

Recipients of the Johnson & Johnson COVID-19 vaccine are at greater risk of getting a rare but severe autoimmune disorder that can lead to paralysis or even death, according to a new study. 

Scientists analyzed data from the Centers for Disease Control and Prevention's (CDC) Vaccine Safety Datalink. Researchers discovered 21 potential cases of Guillain-Barré syndrome (GBS). Eleven of the cases were confirmed. The study has not yet been peer-reviewed, and researchers warn that it "should not be used to guide clinical practice."

The syndrome causes a person's immune system to attack the body's nerves. According to the Centers for Disease Control and Prevention, it causes "muscle weakness and sometimes paralysis. GBS can cause symptoms that last for a few weeks to several years. Most people recover fully, but some have permanent nerve damage. Some people have died of GBS."

In most cases, people develop GBS after battling another severe illness involving diarrhea or respiratory issues, or even after getting the flu. It is very rare, but someone may develop GBS after receiving any vaccine.

About one in 100,000 people develop GBS under normal circumstances. Of those who took the Johnson & Johnson vaccine, the incidence rate of confirmed GBS cases is 34.6 in 100,000 within three weeks of receiving the shot. Most people who developed GBS did so within 13 days of receiving the Johnson & Johnson vaccine.

The Johnson & Johnson vaccine uses traditional vaccine technology, not mRNA like Pfizer and Moderna. The mRNA COVID vaccines had a much lower incidence rate of 1.4 in 100,000 developing GBS within 3 weeks.

The mRNA vaccines are not completely without risks. Both Pfizer and Moderna have been linked to heart inflammation, also known as myocarditis, in males under 30, but those affected generally recover fully.