Of the 100 preliminary reports of Guillain-Barré syndrome, 95 were serious.

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The US Food and Drug Administration (FDA) has released a new warning that the one-dose Johnson & Johnson (Janssen) COVID-19 vaccine could increase people's risk of developing Guillain-Barré syndrome (GBS), a rare neurological disorder.

The FDA added the warning to the vaccine's fact sheet on Monday. The announcement comes after an analysis of the data from the Vaccine Adverse Event Reporting System (VAERS)—a national early warning system to detect possible safety problems in vaccines licensed in the US—showed that 100 people reportedly developed GBS after receiving the Johnson & Johnson COVID-19 vaccine, an FDA official tells Health in an email. Of the 100 cases, 95 were labeled as serious and required hospitalization; one person died.

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Credit: Getty / Photo Illustration by Jo Imperio

"Although the available evidence suggests an association between the Janssen vaccine and increased risk of GBS, it is insufficient to establish a causal relationship," the FDA says. Still, the FDA has issued the warning. So, too, has Johnson & Johnson itself. "While the chance of having this occur is very low, Johnson & Johnson has updated its COVID-19 Vaccine Factsheet to include important information about these rare cases and on the signs and symptoms of Guillain-Barré syndrome," the company said in a statement on Monday.

Here's what you need to know about GBS—and whether the new warning should impact your decision to get vaccinated.

What is Guillain-Barré syndrome?

GBS is a rare autoimmune disorder in which the body's immune system damages nerve cells, causing muscle weakness or sometimes even paralysis, according to the Centers for Disease Control and Prevention (CDC).

The first symptom of GBS is usually a weakness or tingling sensation in both legs. That feeling oftentimes spreads to the arms or upper body. These symptoms can worsen to the point where some muscles can no longer be used. And in severe cases, someone with GBS can become paralyzed. "Symptoms can progress over hours, days, or weeks, and weakness typically peaks within the first two weeks after symptoms appear," according to the CDC. The symptoms can last for a few weeks to several years. And while most people do fully recover, some can experience permanent nerve damage or even death.

Again, GBS is rare—both for the general public and for those who've received the Johnson & Johnson COVID-19 vaccine. Overall, GBS affects about 1 in 100,000 people—in the US, it's estimated that 3,000 to 6,000 people develop GBS each year. When looking at just the people who've gotten the Johnson & Johnson vaccine, the 100 preliminary reports of GBS are among nearly 13 million people in the US who have received a Johnson & Johnson vaccine.

Why is the vaccine causing an increased risk of Guillain-Barré syndrome?

It's actually not unheard of for vaccines to trigger GBS. Although rare, people have developed GBS in the days or weeks after receiving other types of vaccines, including certain seasonal flu vaccines and a vaccine to prevent shingles. The FDA points out that, of the COVID vaccines approved for use in the US, it's only the Johnson & Johnson vaccine that seems to have a link to an increased risk of GBS and that "no similar signal has been identified with the Moderna and Pfizer-BioNTech COVID-19 vaccines."

But a vaccine is not usually the cause behind a case of GBS. Instead, the syndrome's main risk factor is Campylobacter jejuni, which is a bacteria that causes diarrhea. In fact, as many as 40% of GBS cases in the US are thought to be triggered by Campylobacter infection, per the CDC. People can also develop GBS after other infections, including the flu, Epstein Barr virus, and Zika virus.

How long after the COVID vaccine do Guillain-Barré syndrome symptoms develop?

Even though it's extremely rare, it's still important to keep an eye out for potential symptoms of GBS following a vaccine. For most of the 100 people who reportedly developed GBS after their COVID vaccine, symptoms began within 42 days after their vaccination, according to Johnson & Johnson.

Of course, researchers are still studying the link when it comes to the COVID-19 vaccine specifically. But "learning from other cases of non-COVID, post-vaccine GBS, symptoms can emerge anywhere from a few days to a full month post-vaccine," David Putrino, PhD, director of Rehabilitation Innovation for Mount Sinai Health System in New York City, tells Health.

When should you see a doctor if you have symptoms of Guillain-Barré syndrome following a COVID vaccine?

Again, some of the first symptoms of GBS are tingling and weakness in the extremities, often starting with your feet. "Suddenly experiencing these symptoms can be very concerning for many people who are otherwise healthy, and if you're feeling them, you should speak with your doctor immediately to get to the bottom it," says Putrino.

On top of weakness or tingling sensations that are worsening and spreading to other parts of the body, the FDA says to seek medical attention if you experience any of the following symptoms after your Johnson & Johnson vaccine:

  • Difficulty walking
  • Difficulty with facial movements, including speaking, chewing, or swallowing
  • Double vision or inability to move eyes
  • Difficulty with bladder control or bowel function

How is Guillain-Barré syndrome diagnosed?

Especially in its early stages, GBS can be difficult to diagnose, says Putrino. That's because the initial signs and symptoms can look similar to several other disorders.

"GBS is diagnosed through the combination of clinical/neurological examination, generally by an experienced neurologist," Dennis L. Kolson, MD, PhD, a professor of neurology at Penn Medicine, tells Health. According to the National Institute of Neurological Diseases and Stroke (NINDS), a physician can tease out certain indications of GBS, including physical symptoms or weakness on both sides of the body (a key finding in GBS), and a quicker onset of symptoms.

Dr. Kolson adds that a diagnostic test known as a nerve conduction velocity (NCV) test can also provide clues to a diagnosis. Per the NINDS, an NCV test measures nerves' ability to send signals—and in GBS, the signals that travel along nerves slow down. In some cases, a spinal tap may also be necessary, the NINDS says, as there can be a change in the cerebrospinal fluid in people with GBS.

How is Guillain-Barré syndrome treated?

The good news is that "the vast majority of patients make a full recovery from GBS," according to Putrino. To get to that point of a full recovery, he says there are two main phases of treatment to complete.

The first phase of treatment occurs when the nerves are being attacked by the body's own antibodies and you start to lose control of voluntary muscle contractions. "Typically the approach during this period is to make sure that the patient gets all the support they need as the paralysis spreads through the entire body," Putrino explains. "This includes making sure that they can breathe effectively (some cases require ventilation), being careful that prolonged bed rest doesn't lead to pressure sores or skin breakdown, and performing regular, passive joint movements and stretches to ensure that they maintain good mobility while they cannot move."

The therapeutic treatments during this phase includes plasma exchange (which may work by removing the bad antibodies that have been damaging the nerves) or high-dose immunoglobulin therapy (which can lessen the immune attack on the nervous system), according to the NINDS. And while controlled clinical trials have shown that the treatment is ineffective, anti-inflammatory steroid hormones (aka corticosteroids) have also been used as a potential way to reduce GBS severity.

Once the nerves begin to regenerate, you can start the second phase of treatment: intensive physical therapy. This will allow you to regain lost muscle strength and joint mobility.

For the most part, once treated, there are very few long-term consequences of GBS, according to Putrino. In some rare cases where the muscle paralysis was extremely severe and long-lasting, permanent weakness in the hands and feet can sometimes happen. But usually, GBS "rarely recurs or requires continuous management," he says.

Should the risk of Guillain-Barré syndrome prevent you from getting vaccinated?

The short answer here: No. "The FDA has evaluated the available information for the Janssen COVID-19 Vaccine and continues to find the known and potential benefits clearly outweigh the known and potential risks," the agency said.

Pointing to the fact that GBS is "an extremely rare" side effect of the COVID vaccine, Putrino says the new warning shouldn't affect someone's decision to get vaccinated. "The benefit of being vaccinated still far outweighs the risk of GBS from the vaccine," he says.

While Dr. Kolson agrees, saying that "this risk is very, very low, and the benefit of the vaccine in preventing COVID and its complications is huge," he does understand that the news will raise concerns with some people who are still hesitant about getting vaccinated against COVID. "These individuals should discuss the issue earnestly with their physician-providers, as the risk of getting complications (both short-term and long-term) from COVID itself is much greater than the very low risk of GBS with the vaccine. It is too risky to not get vaccinated," says Dr. Kolson.

That advice to get vaccinated comes from two experts in neuroscience, the field that manages GBS. From the perspective of an infectious disease expert, the opinion is the same. "When you look at the rarity of this complication and integrate it with the fact that we are still in a pandemic and which hundreds are dying every day in the US, the risk-benefit calculation still strongly favors the Johnson & Johnson vaccine," Amesh A. Adalja, MD, senior scholar at the Johns Hopkins Center for Health Security tells Health. "I am still recommending this vaccine my friends who desire a single-shot solution to COVID."

As Dr. Adalja points out, when millions of people are getting vaccinated, side effects are going to be detected, and "people should feel confident that the vaccine safety monitoring systems are working as designed and that a lot of attention is being made to publicize even rare side effects so that people are fully informed."

The information in this story is accurate as of press time. However, as the situation surrounding COVID-19 continues to evolve, it's possible that some data have changed since publication. While Health is trying to keep our stories as up-to-date as possible, we also encourage readers to stay informed on news and recommendations for their own communities by using the CDCWHO, and their local public health department as resources.

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