Synopsis About 12.8 million people — or about 8% of the fully vaccinated population in the United States — have received the Johnson & Johnson shot. Agencies The Food and Drug Administration warned Monday that Johnson & Johnson’s coronavirus vaccine can lead to an increased risk of a rare neurological condition known as Guillain-Barré syndrome, another setback for a vaccine that has largely been sidelined in the United States. Although regulators have found that the chances of developing the condition are low, they appear to be three to five times higher among recipients of the Johnson & Johnson vaccine than among the general population in the United States, according to people familiar with the decision. The warning was attached to fact sheets about the vaccine for providers and patients.