Health officials will today seek to reassure parents, advising them to continue immunising their babies against a range of infectious diseases before the new five-in-one jab arrives in late September.
They will insist that the current combination inoculations, given at two, three and four months, are safe and effective but suggest that the changes this autumn will cut still further the already very small risks of children being damaged by vaccines.
They will also confirm that further vaccines in the childhood immunisation programme are being considered - a move that will require confronting the fears of families who think existing jabs overload infants' immune systems.
The officials do not want concerns over the inoculation against diphtheria, tetanus, whooping cough, polio and hib, and Haemophilus influenzae, to reignite similar safety rows to those which arose over the measles, mumps and rubella jabs (MMR), which are first given at 12-15 months.
More than nine in 10 children across Britain have had their first-year jabs. Even the MMR rates have now climbed above 80% for children up to the age of two years.
David Salisbury, the head of immunisation policy at the Department of Health, and Elizabeth Miller, head of immunisation at the Health Protection Agency, will today insist the main driver for change came from the need to alter the way the polio vaccine is given - as part of a combination jab rather than as drops.
The polio vaccine is "live" carrying a small risk, of between one in 500,000 and one in a million, of paralysing a baby or someone coming in contact with the vaccine. Now that polio has nearly been eradicated worldwide, the time is right for an inactivated vaccine, they will say.
The whooping cough vaccine uses thiomersal, a mercury-based preservative that has been linked to autism in one US study, but the government insists that no such link has been found by other British, American and Danish studies. The vaccine is being replaced because "it is consistent with a move to avoid environmental exposure to mercury". The replacement will also contain fewer antigens - elements which provoke an immune response - so may entail fewer side-effects.
The government's joint committee on vaccinations and immunisation is also considering introducing a vaccination against bacterial meningitis for very young children.
Although the timing and dosage of this meningitis jab, as part of a national programme, have not been determined, trials have already seen babies being given this jab alongside the new five-in-one and the meningitis C vaccine simultaneously.
Professor Miller said yesterday: "It is not an immune question, it is a parental attitude question."
Vaccination against hepatitis B may also be added to the list, though debate on whether it is needed within a national programme continues.
Much to some parents' concern, vaccines which do not include the whooping cough element are no longer available to children under 10. Health officials say there has been no big demand, and that the combined diphtheria, tetanus and pertussis jabs have been around for 40 years.
Jackie Fletcher, of the campaign group Jabs, said there ought to be a public inquiry into the way the immunisation programme was being organised. Government advisers and drug companies were not taking responsibility when children came to harm, she said.
Ms Fletcher added: "Parents are picking up the pieces when they were not aware they were at any risk at all." They were also being given fewer opportunities to choose single vaccines, she said.
