When a maverick doctor first raised the issue of the safety of MMR his findings were roundly dismissed by almost the whole medical establishment. The story would have ended there and then except some bright spark in the Westminster lobby decided to ask if Blair's baby Leo had had the jab. The last people you would want to become involved in any row about the safety of the inoculation would be politicians, which is why Blair was asked the question. Some of the press wanted a row and they certainly got one.
When Blair refused to answer, he no doubt had in mind the Tory agriculture minister John Gummer forcing his daughter to eat a hamburger at the start of the 'Mad Cow' disease outbreak in 1990 in a vain attempt to convince the public that beef was safe. It wasn't, and some people are still dying as a result.
Blair, however, should have followed the lead given by the health minister Yvette Cooper, who didn't hesitate to tell us that her first born had had the MMR vaccine and that her new baby would too as soon as he was old enough. She was also one of the very few Labour MPs to admit to smoking cannabis when the Government still thought it was as dangerous as heroin.
Blair's spin doctors, however - no doubt heavily influenced by Cherie - decided that what happens to Leo was none of our business. The obsession with keeping their kids out of the limelight when it suits them took priority over common sense.
It seems that it is all right for Euan to be photographed at a film premiere with Kate Winslett but not for us to know which posh university he is hoping to go to. Leo can be paraded on the steps of Number 10 but apart from that everything about him is private.
The fact is that if Blair had just told us that Leo had the MMR jab straight away it would have got a few paragraphs in the papers and the story would have been dead. Instead we have near panic as people refuse MMR and inevitable outbreaks of measles occur - soon a baby will be dead.
Having realised their mistake, press officers at Number 10 have been busily briefing trusted hacks that of course Leo has had the jab. But it's too late - the damage has been done. It is obvious that Blair now regrets not coming clean on Leo but he can't seem to admit that he was wrong in the first place.
The PM may have screwed up but there is something quite sickening about the Tory opposition fanning the flames of panic among parents. I am old enough to remember the scare about whooping cough inoculation, which ended with 100 dead children.
It's not just the Tories who have been prepared to put children's lives at risk. In Scotland the SNP has been at it, too.
Never mind a new MMR PR campaign, Blair should report to the Commons on his Africa trip and tell the opposition how many babies there die of measles every year. That would shut the Tories up.