Tory leader David Cameron says his new baby will have the MMR jab but suggests single injections should be considered.
David Cameron says baby Arthur will have the MMR jab
He has already said his other children have been given the vaccination in contrast to Tony Blair who has refused to disclose whether his son has had it.
But he reopened the debate about single jabs saying if the uptake falls the NHS should consider individual injections.
Health experts there was no evidence that single vaccines were safer for children than MMR.
Last year 81% of two-year-old's had the jab - up on the year before but short of the 95% needed for herd immunity.
When 95% of the population have been vaccinated, protection is provided to everyone whether or not they are vaccinated themselves.
Mr Cameron became a father for the third time two weeks ago when his wife, Samantha, gave birth to Arthur.
The couple have a three-year-old son, Ivan, and two-year-old daughter, Nancy.
He said: "My children have had the MMR vaccine and the new one will have it.
"But I think the NHS needs to look out very carefully. If the amount of children having the injection falls, it has to look at how to encourage parents and that might mean single jabs."
The rise in the vaccination rate in England last year from 80% was the first since doubts were cast on the safety of the vaccine - which protects against measles, mumps and rubella.
Research which linked the jab to autism has since been discredited - but uptake rates remain below official targets.
Concern over the jab was sparked by a paper published in The Lancet in 1998 by Dr Andrew Wakefield.
The same journal published a study last year concluding that there was no evidence to support a link between MMR and autism.
Throughout the controversy, the prime minister has refused to say whether Leo had the jab.
Liberal Democrat science spokesman Dr Evan Harris MP said expert advice was quite clear that separate jabs are less effective than single jabs.
"In his first pronouncement on science matters since becoming party leader, David Cameron has stated that the Tories would reject independent expert scientific advice and want the government to do so.
"It is opportunistic populism not responsible opposition."
Sir Liam Donaldson, the chief medical officer for England, told London's Evening: "There is no evidence that single vaccines are in any way 'safer' than MMR, and strong evidence that they put the child and other children at risk."