WEDNESDAY, Oct. 18, 2023 (HealthDay News) -- COVID infection can raise the risk of a rare immune system attack on the body's nerves -- but vaccination might protect against it, a large new study suggests.

The study, of more than 3 million Israeli adults and teenagers, found that COVID infection was linked to a substantially increased risk of developing Guillain-Barre syndrome in the next six weeks.

GBS is a rare condition where the immune system launches a misguided attack on the body's own nerve tissue. It causes symptoms like weakness and tingling in the limbs, difficulty walking and even paralysis.

Experts said it's no surprise that COVID would raise the odds of GBS: When the condition occurs, it's often in the weeks following a respiratory or gut infection. Researchers believe that's because that ordinary infection, in rare cases, sets off a haywire immune response.

"I would be surprised if COVID infection did not increase the risk of GBS," said Dr. Dennis Bourdette, a professor emeritus of neurology at Oregon Health & Science University.

More noteworthy, he said, is the study's other major finding: GBS was less common in people who'd recently been vaccinated against COVID than in those who hadn't.

In Israel, the Pfizer mRNA vaccine is by far the most commonly used jab against COVID. When people received it, the study found, their risk of developing GBS in the next six weeks was 50% lower, versus people without a recent vaccination.

That's important because certain vaccines have been tied to small increases in the risk of GBS -- including the Astra-Zeneca and Johnson & Johnson COVID vaccines, which are not mRNA-based.

The new study, Bourdette said, "suggests that COVID mRNA vaccines not only do not cause GBS, but may protect against developing GBS."

Bourdette wrote an editorial published with the findings in the Oct. 18 issue of Neurology.

Another U.S. expert called the study "very important."

"It clearly shows that COVID itself poses a significant risk of GBS, and that the vaccine, in fact, will prevent cases of GBS," said Dr. Aaron Glatt, chief of infectious diseases at Mount Sinai South Nassau in Oceanside, N.Y.

It's "yet another reason," Glatt said, for people to keep up with the recommended COVID vaccinations.

For the study, researchers led by Dr. Anat Arbel, of Lady Davis Carmel Medical Center in Haifa, Israel, tracked medical records from nearly 3.2 million Israeli patients age 16 and older. At the outset, in January 2021, none had a history of GBS.

During the study period, which ran till June 2022, 76 people were diagnosed with GBS. The researchers compared each of those patients with 10 other individuals of the same age and sex who were free of GBS.

It turned out there was a clear link between COVID and the nerve condition. Of the group with GBS, 12% had been infected with COVID within the past six weeks, versus only 2% of the comparison group.

Looked at a different way, people with a COVID infection within the past six weeks were over six times more likely to develop GBS than people who were COVID-free during the same time period.

The picture changed, however, when it came to COVID vaccination. People who developed GBS were less likely to have been vaccinated within the past six weeks, compared with people who did not develop GBS -- less than 11%, versus 18%.

It's unclear why the vaccine might lower the risk of GBS, Bourdette said. One obvious possibility, he said, is that it prevents some GBS cases by preventing COVID.

But Bourdette also speculated that the mRNA vaccines might lower the odds in other ways.

"It's worth considering the possibility that COVID mRNA vaccination might induce non-specific immune changes that reduce the risk of developing other viral infections associated with GBS," he said.

Further studies, Bourdette added, would be needed to answer that question.

For the average person, both doctors said the findings offer more reassurance on the safety of mRNA vaccines against COVID.

"Anyone who is afraid of getting GBS from a COVID mRNA vaccine should be reassured that at least this type of COVID vaccine does not cause GBS," Bourdette said. "And it may actually reduce the risk."

More information

The U.S. Centers for Disease Control and Prevention has more on vaccines and Guillain-Barre.

SOURCES: Dennis Bourdette, MD, professor emeritus, neurology, Oregon Health & Science University, Portland; Aaron Glatt, MD, chief, infectious diseases and hospital epidemiologist, Mount Sinai South Nassau, Oceanside, N.Y., and professor, medicine, Icahn School of Medicine at Mount Sinai, New York City; Neurology, Oct. 18, 2023, online