Sarah and Christopher Fisher said they believed the jab was “implicated” in the sudden death of their son George.
The inquest heard how George had suffered an epileptic-type fit four months before being given the MMR vaccine and that this might have been a warning he could react badly to the jab.
However, a consultant told the inquest that while it had been deemed safe to give the child the innoculation against Measles, Mumps and Rubella, his parents should have been told to monitor his temperature.
Mrs Fisher, 42, a hotel receptionist, said she had not been given any information about what symptoms might signal an adverse reaction to the jab.
The inquest heard how George was found dead in his cot on the morning of January 19, 2006.
Mrs Fisher, who has three other children, said George had been happily playing football with his father the day before he died. He went to bed as normal about 7pm.
Before Mrs Fisher went to bed at 11.30pm she heard him “chatting away” on the baby monitor. She made a final check on him, turned him onto his back, put the quilt over him, stroked his head, and said goodnight.
She heard him drink from his bottle and then throw it down on the floor before shuffling around to get comfortable.
At 8am next morning, she said, her daughter Megan, who shared a room with George, called out to her.
“I put her in our bed. I glanced at George as I went into the bathroom and was surprised he was not yet awake.
“I went to try to wake him up but it was clear to me he was dead because of his colour and he was cold.”
She added: “We simply cannot understand why our healthy 18-month-old son died 10 days after the MMR vaccination.”
The inquest heard that Department of Health guidelines say that children like George who have suffered a fit brought on by a high fever, known as a “febrile convulsion”, should be given MMR but “with caution”.
Consultant paediatrician, Alan Day, of Cheltenham General Hospital, agreed that George was safe to be given the vaccine on January 9 2006 – adding that he should be monitored for the warned raised temperature.
Dr Day said his advice to parents whose child had suffered a febrile convulsion before being given the vaccine would be to take paracetamol and “purchase a good thermometer”.
But Mr Fisher, a pipe-fitter, said that no Patient Information Leaflet on the MMR precautions to be taken with children who had previously suffered fever had been given to the family. Nor was any verbal advice specific to his circumstances.
George was given his MMR vaccination but he showed symptoms of lost appetite, red eyes, and diarrhoea before he died on Jan 19.
His parents said that had they seen the patient information leaflet they might have taken more notice of their son’s temperature fluctuations after the MMR vaccination and taken him to hospital.
Instead they had made an appointment with their GP, but George died before it could be kept.
Paediatric pathologist Dr Nikola Ostojic said George died as a result of oedema – fluid – on the lungs. But he could not identify a reason for the leakage and gave the cause of death as unascertained.
He said a possible explanation might be a “heart insufficiency” but could not be sure.
Professor Elizabeth Miller, an immunisation expert for the Heath Protection Agency, said the MMR jab can cause a febrile convulsion in one child in two to three thousand.
She said the febrile convulsion would be expected to occur between six and 14 days after an MMR jab.
But Prof Miller could see no direct link between the jab and the child’s death.
She said: “Fatal outcomes associated with MMR vaccination as a result of febrile convulsion have not to my knowledge been reported.”
Professor of Infant Health, Peter Fleming, of Bristol University, said it was most likely that George died from a rare type of seizure known as Sudden Unexpected Death in Childhood.