IT fell to me, his gran, to take my eleven-month-old grandson for his first MMR jab. His mother had wanted to spare me that.

She'd arranged to take him one day when I was away on holiday, but he went down with a cold so it had to be put off. By the time he was better, she was back at work and I was minding him again. My daughter-in-law was full of apologies. She was concerned for me as well as the baby. That morning, she said: "If anything goes wrong, I don't want you to feel bad about it."

He likes the doctor and he hardly noticed the jab. He looked a bit surprised - "hey, what was that?" - but the next moment had spotted a toy and wriggled off my knee in search of it. He was half way across the floor by the time I was on my feet. I put him in his pushchair and wheeled him home in time for Teletubbies. There was no sign of any immediate adverse reaction, nothing to make me feel bad. It was not much different from all those occasions, 30-odd years ago, when I'd taken my own children for their routine injections.

But it was different. Then, I hadn't given it a second thought. All babies had their jabs as a matter of course. It was for their good and for the good of society. Life-threatening diseases such as smallpox had been wiped out for ever by means of mass vaccination.

In fact, until our grandson was born that's exactly how I'd continued to look at it. Long before I'd even dreamed I was going to be a grandma, I'd known about the panic over the MMR vaccine. Was it linked to autism? Could it leave your happy little boy (autism mostly affects boys) withdrawn, unsociable, in a world of his own? I wasn't then a grandmother, but I was the mother of an adult daughter with a compromised immune system as a result of treatment for a serious illness. I looked at things from her point of view.

I read all the reports in the papers and it seemed clear to me: the evidence showed there was no proven link between MMR and autism. A doctor friend I spoke to was having his son vaccinated as a matter of course. I felt angry with mothers who refused to let their children have the vaccine. There was a real risk of an epidemic. Measles can cause lasting damage, particularly blindness, though it's not generally a killer, not in otherwise healthy children. But for the frail, the elderly, the very young, for anyone with a dodgy immune system - like my daughter - it can be life-threatening.

Then our grandson came into the world and it all looked much less clear-cut. It did to his parents too. Everyone speaks about choice as if it were always a good thing. It isn't. It can make life very difficult, much more complicated. When things go wrong, it can lead to terrible guilt and anguish.

My daughter-in-law talked to her doctor, to the clinic nurses, to her friends, and read everything on the subject she could lay her hands on, in newspapers, on the Internet. She and my son discussed the subject endlessly. They both came to the same conclusion as I had: there isn't a proven link between MMR and autism. Children aren't generally born with signs of autism; it develops later. It's just a coincidence that autism tends to show itself around the time of the MMR vaccination. On the other hand, measles can be very serious, especially for a generation who have had no contact with the disease. It's not just a matter of protecting your own child, it's all the other children too.

So, they decided to go ahead. It was the rational, sensible thing to do. It was the socially responsible thing to do. It was for the good of their child. Besides, he was about to start nursery - a very good nursery, chosen after much looking around - and it wouldn't take him unless his vaccinations were up to date.

But you can't switch off your fears that easily, especially where your children are concerned. There's still a sneaky little voice saying: "What if all the experts are wrong after all? What if there is a link, if one day a new study proves it's there? What then? We'll know, too late, that we may have done terrible harm to our child."Well, he had the jab. That was well over a year ago, and he's still a happy, friendly little boy. There'll be the second vaccination, of course, just before he starts school, which will bring all the worries back again.

I'm just thankful I'm not the one who had to make the decision.