A box of Janssen COVID-19 vaccine doses from Johnson & Johnson is pictured in Grubbs Pharmacy on Capitol Hill on Monday April 12, 2021.

Tom Williams | CQ Roll Call, Inc. | Getty Images

The Food and Drug Administration is expected to announce a new warning for Johnson & Johnson’s Covid-19 vaccine stating the shot has been linked to a serious but rare autoimmune disease, the Washington Post reported Monday citing four unnamed sources.

About 100 preliminary reports of Guillain-Barre syndrome were discovered after 12.8 million doses of the J&J vaccine were administered, the Centers for Disease Control and Prevention said in a statement to NBC News. Guillain-Barre is a rare neurological disorder in which the body’s immune system mistakenly attacks part of the nervous system.

It is estimated that around 1 in 100,000 people are affected each year, and most people eventually recover from the disorder, according to the National Institute of Neurological Disorders and Stroke.

The cases reported after receiving the J&J syringe mostly occurred around two weeks after vaccination and mostly in men, many of whom were 50 years of age and older, according to the CDC. The data available does not show a similar pattern with the Pfizer or Moderna vaccine, the agency said.

U.S. regulators are expected to emphasize that the J&J vaccine is safe and that its benefits significantly outweigh the potential risks, the Post reported, citing people familiar with the situation.

The FDA did not immediately respond to CNBC’s request for comment.

“Reports of GBS following receipt of the J & J / Janssen COVID-19 vaccine in the Vaccine Adverse Event Reporting System (VAERS) are rare, but likely indicate a small potential risk of this side effect after receiving this vaccine,” the CDC said in the statement NBC News.

In a statement Monday, J&J said it had discussions with the FDA and other regulators about the disorder.

“The likelihood of this occurring is very small, and the rate of reported cases is slightly higher than the background rate,” the company said. “We strongly support raising awareness of the signs and symptoms of rare events to ensure that they can be identified quickly and treated effectively.”

The awaited new warning is just the latest setback for J&J, who has suffered production problems with its vaccine as well as public concerns about a rare, potentially life-threatening blood clotting disorder related to its vaccinations.

After its approval in late February, the vaccine was touted as a blessing as it could be stored for months at refrigerator temperatures and only required one dose – unlike those from Pfizer and Moderna, which require more complicated transportation methods and are two doses.

More than 12 million of the J&J shots were administered in the United States, according to data compiled by the CDC.

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