A judge has ruled that sisters aged 15 and 11 must have the MMR vaccine even though they and their mother do not want it, BBC Newsnight has learned.
The High Court decision, made last month, came after the girls' father brought a case seeking vaccination.
The parents, now divorced, had agreed when married not to vaccinate the girls in the wake of the MMR controversy.
But the discrediting of concerns about an MMR autism link and recent measles outbreaks changed the father's view.
This is the third time this issue has come before the court.
In 2003 a mother was ordered to have her child immunised against measles, mumps and rubella after the court ruled the benefits of vaccination outweighed the risks. In 2011, children in care were ordered to have the MMR jab against the wishes of their parents.
'End of MMR debate'
When outlining her decision in the latest case, Mrs Justice Theis emphasised it was a specific case "only concerned with the welfare needs of these children", but lawyers say as one of a series it confirms there is no longer any debate about the benefits of the vaccine.
Measles is a highly contagious disease characterised by a high fever and a rash.
In one in 15 cases it can lead to severe complications, such as pneumonia, and in a very small number of cases it can cause encephalitis - inflammation of the brain - which can cause brain damage or even death.
MMR is a combined vaccine against measles, mumps and rubella, three common infectious diseases of childhood. It was introduced in the UK in 1988 to replace single vaccines for each disease.
The first MMR vaccine is given as a single injection to babies as part of their routine vaccination schedule, usually within a month of their first birthday, then a second injection of the vaccine, known as the MMR booster, is given before starting school.
The first gives about 95% protection against measles, while two doses give 99-100% protection.
In 1998, a study by Dr Andrew Wakefield was published in the respected medical journal The Lancet raising the possibility that the MMR jab was linked to autism and bowel disease.
The report and the media furore that followed prompted many parents to decide against having their children vaccinated with the three-in-one injection, including the parents of the two girls at the heart of this case.
The elder daughter was given the first injection, but not the booster vaccine; the younger daughter did not receive any vaccinations at all - decisions made jointly by both parents at the time.
However, in 2010 Dr Wakefield's research was found by the General Medical Council to have been "dishonest" and has since been entirely dismissed.
The father of the two girls says that this change, combined with an outbreak of measles in Swansea late last year, changed his mind in January 2013 about whether his daughters should be given the MMR jab. He says he was worried these diseases could have serious consequences.
According to the text of the court decision, seen by BBC Newsnight, the father's solicitor wrote to the girls' mother in January seeking her agreement that they should now be vaccinated, and saying that if she did not agree he would take the matter to court.
The mother did not agree and the matter eventually came before the Family Division of the High Court.
A court-appointed welfare officer who spoke extensively to the girls said that neither of them wanted the vaccination.
The children were particularly concerned about the ingredients in the vaccine, which include animal-based materials; one of the girls is a vegan.
However, the officer said that when she asked them what would happen if they became ill with measles, mumps or rubella and needed medicine, they clearly had not thought about what the ingredients in that medicine might be.
The welfare officer said both children had been strongly influenced by their mother, who was very anxious about the jab.
Mrs Justice Theis decided that it was in the best interests of the children that they were vaccinated.
"I am aware that this is against the girls' wishes but that it is not the only factor," she wrote. "The court also has to consider their level of understanding of the issues involved and what factors have influenced their views. I do not consider there is a balanced level of understanding by them of the issues involved."
The mother's lawyer Philippa Dolan told Newsnight that the girls had not yet been vaccinated despite the deadline to do so having passed on Thursday.
She said: "There are practical difficulties in enforcing the order and that is at the moment an ongoing issue. There's not a legal deadline that's a serious issue the parents are in discussion and everyone hopes it will be resolved without any more litigation."