There is no evidence that the triple MMR jab causes immune system overload and, if anything, the injection seems to protect children, according to new research in Britain.
The findings go against the idea that exposure to three live viruses through the injection could leave children more vulnerable to serious bacterial infection.
It had been argued that the effect of the jab on the immune system could lead to persistent viral infections and even bowel problems or autism. Such fears had prompted some parents to refuse to give their child the measles, mumps and rubella (MMR) vaccine.
The research, published today in the journal Archives of Disease in Childhood, has been welcomed by Dr Brian O'Herlihy, a specialist in public health medicine with the Eastern Regional Health Authority.
"I would hope it would allay the unwarranted fears a small number of parents have in relation to the use of the vaccine," he said.
"The findings don't surprise me in the least, because a whole range of international bodies and experts have come out strongly in favour of MMR, and they have all agreed independently that it's a very safe vaccine," he added.
Dr O'Herlihy said that the Republic was witnessing the beginning of another outbreak of measles, with a significant number of cases having been reported since Christmas. He urged parents to have their children vaccinated to protect them.
However, Ms Kathy Sinnott, whose son is autistic, dismissed the research as another piece of "number-crunching" epidemiology. "When are we going to have primary research to show it's perfectly safe?" she asked, pointing out that only primary research had linked the vaccine to autism.
She stressed that she was not against MMR, but she wanted children screened before vaccination.
The research was carried out by the Public Health Laboratory Service in the UK. It said that if MMR did suppress the immune system significantly, then there should be more cases of infection in the period just after children had the jab.
The researchers looked at data from hospitals in the former Thames region in southern England from April 1991 and March 1995. They monitored all cases of serious bacterial infection, such as septicaemia, meningitis and pneumonia, among children aged between one and two who were admitted to hospital within three months of the MMR jab. They identified 436 such admissions, but found no evidence that the MMR jab increased their risk of serious infection. In fact, they found that it seemed to protect children against the risk of pneumonia.
Furthermore, they said that their findings did not support calls for single mumps, measles and rubella jabs to be provided.
Additional reporting by PA