TUESDAY JANUARY 22 2002

BY DR JANE COLLINS

The Times children's doctor answers readers' questions

Q: Do post-measles babies still need the MMR jab?

My two elder sons both had the MMR vaccination because I was prepared to accept that risks from the vaccination were lower than the risks from the diseases themselves. My youngest son is now due for his MMR but contracted measles at the age of nine months. My health visitor says that he should still have the triple vaccine, but I feel I am being fed the party line because I know that my surgery does not give single doses. What is your advice?
Amanda Evans, London

A: Your health visitor has given you good advice. Even though your son was diagnosed with measles, it is possible that he could have had something else. A previous clinical diagnosis of any of the three diseases — measles, mumps or rubella — is not a reliable indicator of whether or not a child had the disease. Tests carried out two years ago to confirm measles found that only 75 of 1,750 reported cases were truly measles. The rest were other illnesses. But as uptake of the MMR vaccine has fallen, especially in London, we are increasingly at risk of seeing these three diseases again.

You might think that a blood test would reveal whether your son is immune to measles. In fact blood tests available to check for immunity are designed to confirm an acute measles infection and have not been validated as a means to detecting reliably for immunity.

Even if your son is immune, there is no problem with him receiving the MMR vaccine. MMR contains three live but weakened viruses. Each vaccine virus will not build up to a significant level in someone who already has immunity to that infection.

The vaccine has a good safety profile, having been given to children under the age of two in the United States for almost 30 years. It is used in more than 90 countries and is highly effective. Its use in the UK has resulted in a dramatic decline in measles, mumps and rubella, but a high vaccine uptake is essential to continue to protect children against these three potentially serious infections.