J&J COVID vaccine may pose 'small possible risk' of rare neurological syndrome, CDC says

The U.S. Centers for Disease Control and Prevention said on Monday that it has received rare reports of Guillain-Barré syndrome among people who got Johnson & Johnson's Janssen shot. The vaccine has been approved in Canada but never used.

Shot has been approved in Canada but never used

Boxes of COVID-19 vaccine from U.S. pharmaceutical company Johnson & Johnson developed with Janssen are pictured at a central vaccine warehouse in Germany. The vaccine only requires one dose and has been approved in Canada but never used here. (Ronny Hartmann/dpa/The Associated Press)

Johnson & Johnson's COVID-19 vaccine may pose a "small possible risk" of a rare but potentially dangerous neurological reaction, U.S. health officials said Monday.

The Centers for Disease Control and Prevention said in a statement it has received reports of 100 people who got J&J's Janssen shot developing Guillain-Barré syndrome, an immune system disorder that can cause muscle weakness and occasionally paralysis.

That number represents a tiny fraction of the nearly 13 million Americans who have received the one-dose vaccine. Most cases of the side effect were reported in men — many 50 years old and up — and usually about two weeks after vaccination.

The CDC said it would ask its panel of outside vaccine experts to review the issue at an upcoming meeting.

J&J didn't immediately respond to The Associated Press's request for comment. 

Earlier on Monday, J&J issued a statement saying it was in discussions with the U.S. Food and Drug Administration about the rare cases of Guillain-Barré. 

"The chance of having this occur is very low," the statement said. The company also said that the number of reported cases of Guillain-Barré after use of the vaccine exceeded the number of cases normally expected in the population by a "small degree." 

The U.S. government said the vaccines most used in the U.S., made by Pfizer and Moderna, show no risk of the disorder after more than 320 million doses have been administered.

Guillain-Barré syndrome occurs when the body's immune system mistakenly attacks some of its nerve cells, causing muscle weakness and sometimes paralysis that typically is temporary. An estimated 3,000 to 6,000 people develop the syndrome each year in the U.S., according to the CDC.

Most people who suffer from Guillain-Barré recover fully, according to the CDC's website, but there have been cases of permanent nerve damage. 

Syndrome can be triggered by flu, other infections

Vaccines historically provide broad protection with little risk but come with occasional side effects just like other drugs and medical therapies. The three COVID-19 vaccines used in the U.S. were each tested in tens of thousands of people, but even such huge studies can't rule out extremely rare side effects.

The CDC and the FDA have been monitoring side effect reports submitted by physicians, drugmakers and patients to a federal vaccine safety database.

Guillain-Barré can be triggered by a number of infections, including the flu, cytomegalovirus and Zika virus. But there have also been rare cases in which people develop the disorder days or weeks after receiving certain vaccines.

J&J's vaccine was highly anticipated because of its one-and-done formulation and easy-to-ship refrigeration. But early on, it was linked to another rare risk, of blood clots, and the company hasn't been able to produce as much as expected because of problems at a Baltimore factory that helps make the shots.

Not used in Canada

Health Canada approved J&J's Janssen vaccine but it has never been used in Canada. There also doesn't appear to be any confirmed plan to do so. 

Public Services and Procurement Minister Anita Anand recently said the Johnson & Johnson contract remains in place and Canada could draw on supplies from this company at a later date.

But with millions more mRNA shots from Pfizer and Moderna set to arrive in the coming weeks, she said shipments from J&J may not be necessary.

With files from John Paul Tasker and CBC News

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