What does it have to do with vaccination?
This is not the first vaccine that has been linked to Guillain-Barré, although the risk appears to be tiny. A large swine flu vaccination campaign in 1976 led to a small uptick in the incidence of syndrome; the vaccine caused roughly one extra case of Guillain-Barré for every 100,000 people vaccinated. The seasonal flu shot is associated with roughly one to two additional cases for every million vaccines administered.
“I think the data are pretty compelling that the flu vaccine causes Guillain-Barré syndrome, but it’s a very small risk,” said Daniel Salmon, the director of the Institute for Vaccine Safety at Johns Hopkins University.
The shingles vaccine Shingrix may also increase the risk of the condition.
It is not entirely clear why some vaccines may cause Guillain-Barré. “We don’t really understand the biological mechanism,” Dr. Salmon said. “It’s an incredible frustration.”
What do we know about its connection to the Covid-19 vaccines?
One hundred reports of the syndrome after vaccination with the Johnson & Johnson shot have been submitted to the federal Vaccine Adverse Event Reporting System (VAERS), officials said on Monday. Of those, 95 cases resulted in hospitalization, and one was fatal.
The syndrome was generally reported about two weeks after vaccination, primarily in men, many of whom were 50 or older, officials said. There is not yet enough evidence to establish that the vaccine causes the condition, but the F.D.A. will continue to monitor the situation, the agency noted in a statement.