The US Food and Drug Administration updated the label on Johnson & Johnson's coronavirus vaccine Monday to warn of the possible increased risk of a rare neurological complication known as Guillain-Barré syndrome.
While the FDA said it had not established the vaccine could cause the syndrome, it noted an increase in reports of the sometimes paralyzing condition.
"Today, the FDA is announcing revisions to the vaccine recipient and vaccination provider fact sheets for the Johnson & Johnson (Janssen) COVID-19 Vaccine to include information pertaining to an observed increased risk of Guillain-Barré Syndrome (GBS) following vaccination," it said in a statement sent to CNN.
"Reports of adverse events following use of the Janssen COVID-19 Vaccine under emergency use authorization suggest an increased risk of Guillain-Barré syndrome during the 42 days following vaccination," the updated label reads.
"Although the available evidence suggests an association between the Janssen vaccine and increased risk of GBS, it is insufficient to establish a causal relationship. No similar signal has been identified with the Moderna and Pfizer-BioNTech COVID-19 vaccines," the label adds.
The FDA said 100 preliminary reports of Guillain-Barré syndrome had been filed with the US government's Vaccine Adverse Reporting System, out of 12.8 million Janssen vaccines given.
"Guillain Barré syndrome (a neurological disorder in which the body's immune system damages nerve cells, causing muscle weakness and sometimes paralysis) has occurred in some people who have received the Janssen COVID-19 Vaccine," the FDA says in the label update for patients and caregivers.
"In most of these people, symptoms began within 42 days following receipt of the Janssen COVID-19 Vaccine. The chance of having this occur is very low," it adds.
People should seek medical attention if they notice symptoms such as weakness or tingling in the arms and legs, especially if it spreads, after receiving a vaccine, the FDA said.
Other telltale symptoms include difficulty walking, speaking, chewing or swallowing; double vision; and bowel or bladder control problems.
The FDA said 95 of the 100 reports of GBS involved people who needed hospitalization, and one person died.
"Each year in the United States, an estimated 3,000 to 6,000 people develop GBS. Most people fully recover from the disorder," the agency added.
"GBS has also been observed at an increased rate associated with certain vaccines, including certain seasonal influenza vaccines and a vaccine to prevent shingles.
Johnson & Johnson confirmed it was talking to the US Centers for Disease Control and Prevention and FDA about the issue.
"We have been in discussions with the U.S. Food and Drug Administration and other regulators about rare cases of the neurological disorder, Guillain-BarreÌ syndrome, that have been reported following vaccination with the Janssen COVID-19 vaccine," the company said in a brief statement.
"The chance of having this occur is very low, and the rate of reported cases exceeds the background rate by a small degree," it added.
Even if the vaccine does raise the risk of the syndrome, it's still better to get vaccinated against the coronavirus, the CDC stressed.
"GBS is a neurological disorder in which the body's immune system damages nerve cells, causing muscle weakness or in the most severe cases paralysis. Each year in the United States, an estimated 3,000 to 6,000 people develop GBS; it is typically triggered by a respiratory or gastrointestinal infection. Most people fully recover from GBS," a CDC spokesperson told CNN.
"Reports of GBS after receipt of the J&J/Janssen COVID-19 Vaccine in the Vaccine Adverse Event Reporting System (VAERS) are rare, but do likely indicate a small possible risk of this side effect following this vaccine," the spokesperson added.
The spokesperson said the CDC's Advisory Committee on Immunization Practices would discuss the matter in an upcoming meeting.
"In the United States, nearly all COVID-19 hospitalizations and deaths are now occurring in unvaccinated people. The risk of severe adverse events after COVID-19 vaccination remains rare. Everyone age 12 years and older is recommended to receive a COVID-19 vaccine," the statement said.
The CDC and FDA briefly paused use of the Johnson & Johnson vaccine earlier this year because of a risk of a rare type of blood clotting complication but lifted the pause in April after determining the risk was low and the condition was treatable. The vaccine's label was updated to warn about the risk.