Johnson & Johnson’s has been issued a warning from the Food and Drug Administration (FDA) after reports of Guillain-Barré Syndrome.
The FDA reported 100 cases with 95 requiring hospitalisation, leaving one person dead with symptoms beginning within 42 days of receiving the J&J jab.
The symptoms generally start within days or weeks of a respiratory or gastrointestinal viral infection, and can result in mild spurts of muscle weakness or more severe forms of paralysis.
So far, about 12.8 million Americans have been given the one-dose vaccine.
While the available evidence suggests a link between the shot and the syndrome, the agency said that the data was insufficient to be able to say 'definitively' the vaccine had caused the illness.
Guillain-Barré Syndrome is a disease that sparks the immune system to attack the nerves.
Between 3,000 and 6,000 people a year develop Guillain-Barré Syndrome, according to the FDA, and most fully recover from it.
The CDC said that the issue will be discussed at an upcoming vaccine advisory committee meeting.
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Despite the new warning, the CDC persisted in advising the risk of severe adverse reactions from Covid vaccines remains 'remote', and that everyone 12 years and older is recommended to receive a vaccine.
Initially, the elderly with pre-existing health issues were cited as the 'at-risk' category, yet as the vaccines are rolling out, COVID-19 is reportedly impacting all age demographics in line with the all-age vaccinations.
The FDA said the benefits of the J&J shot in preventing Covid-19 clearly outweigh known and potential risks yet the science around this recommendation is not known.
According to J&J, the Guillain-Barré cases are rare.
'The chance of having this occur is very low, and the rate of reported cases exceeds the background rate by a small degree,' they said.
The development marks yet another setback for the J&J’s vaccine.
In April, U.S. health agencies urged providers to stop administering the shot to assess rare but serious blood clots that occurred among some people who had received it.
After review, regulators stated the chances of developing the rare blood clot syndrome was very rare, thrombosis, again repeating the 'benefits of the shot outweighed the risks'.
Regulators added information about the minimal risk of the clots to the shot’s fact sheet, noting most cases had occurred in women age 18 through 49 who were not in the demographic of concern for illness or death from the COVID-19 virus in the first instance.
The CDC has long studied the association between the seasonal flu shot and 2009 H1N1 monovalent influenza vaccine and Guillain-Barré, though the agency has suggested the precise risk is difficult to estimate.
Health officials have warned about possible rare side effects with other Covid-19 vaccines.
Last month, the FDA added warnings regarding Pfizer Inc.-BioNTech SE and Moderna Inc. about a risk of possible heart inflammation.
According to the CDC, around 1,200 cases of myocarditis and pericarditis have been reported in people who had received the shots.
The available data doesn't show a pattern of Guillain-Barré Syndrome in recipients of mRNA vaccines, the FDA and CDC said.