A coroner ruled Friday that a common childhood vaccination was not responsible for a baby's death, but the boy's parents disagree, the Guardian reported Friday.

Eighteen-month-old George Fisher died after doctors vaccinated him with the measles-mumps-rubella vaccine while he was sick, the baby’s parents told the coroner at an inquest this week.

Although the parents blame the vaccination, Coroner Alan Crickmore believes the boy died from "natural causes," the newspaper reported.

George was suffering from a febrile convulsion, which occurs in young children when their body temperature rapidly increases, when his parents took him to Overton Park Surgery in Cheltenham, England, to get the shot.

The Fishers believe the vaccine is "implicated" in their son's January 2006 death and that doctors should have warned them that a child suffering from a high fever should not receive the shot.

George died 10 days after being vaccinated.

The couple said they later learned that children who have suffered a convulsion are at a higher risk for having another one after getting the MMR shot. They believe the boy suffered a second convulsion after getting the vaccine.

But Crickmore said George's symptoms emerged too soon after receiving the vaccination to be related to it.

Although George had a 2 percent chance of suffering a convulsion after the shot, there's no evidence he suffered a second convulsion after getting the shot, Crickmore said.

Crickmore believes George died from a rare condition known as sudden unexpected death in childhood, due to an unknown disease.

Click here to see pictures of George and to read more from the Guardian.