Q: “My son is now nearly four and a half and had the MMR vaccine at a year with no significant problems. He has now been called for his second MMR vaccination. Is the vaccine always given in two stages? I have seen several references to it being given as a single injection at 12-15 months, with no reference to a second pre-school injection. Why? All the concerns about MMR also seem to be about the injection at 12-15 months. What is the risk of my child not being immune to a serious condition (particularly measles) if he does not receive the second immunisation?”
A: Since 1996, MMR immunisation in the UK has consisted of two injections, one at between 12 and 15 months, and another at school entry. Literature printed prior to 1996 would have referred to a single injection. The reason a second dose of MMR vaccine is given is that the vaccine does not always work perfectly first time. Around 5-10% of children will remain unprotected after the first dose. A second dose significantly increases the number of children protected.
Side effects from the second dose are even rarer than with the first dose. Those that occur tend to be in the children who did not get protected by the first dose, and these are the children who need the immunisation most. The only alternative to giving a second dose to all children would be to do a blood test on every child to check their immunity. Apart from the difficulty of organising this, and the fact that having a blood test can be quite unpleasant, it is likely that many children who needed a second dose would fail to obtain it. The World Health Organisation recommends that routine testing for immunity is not done, and over 30 European countries, USA, and Canada, all give routine second doses without testing.
Dr Jo Lee, Babyworld Doctor.