The United States Food and Drug Administration, FDA, is limiting the emergency use authorization of the Johnson and Johnson Covid-19 vaccine because of what it describes as, a dangerous side effect.

The FDA announced on Thursday that administration of the vaccine, will be limited to people 18 years and older, who are unable to take another brand of vaccine, or who choose to take Johnson and Johnson because otherwise they wouldn’t be vaccinated.

In a statement, the FDA said that the change is being made because of the risk of a rare and dangerous clotting condition, which developed after some persons received the vaccine.

The FDA said 15 percent of cases have been fatal.

Overall, the risk of the condition is extremely rare, with about three cases, for every one million doses of vaccine administered.

The highest rate of the condition has been in women between 30 and 49 years old.