The 5-in-1 vaccine combines vaccines that are already available and given to children to protect against five diseases:
Haemophilus influenzae type B (Hib) - one of a family of bacteria that cause serious conditions like meningitis and pneumonia.
How is it different?
Currently, children are immunised against all of these diseases at two months but receive polio as a separate oral vaccine which contains a live version of the virus.
Being live means it could potentially cause disease, such as paralysis, in the person having the vaccine and the people they have contact with, but this theoretical risk is extremely small.
The new jab combines polio vaccine with the other vaccines, but in a different form - a dead version of the virus which cannot do harm.
Also, the 5-in-1 vaccine does not contain the mercury-based preservative thiomersal, unlike the current version.
The pertussis part of the vaccine is also new and is designed to cause fewer adverse reactions.
Unlike the conventional whole cell vaccine, which contains the entire inactivated pertussis organism, the acellular vaccine contains elements of the pertussis organism thought to provide protection against the disease.
Therefore it provides the same high level of protection but tends to cause fewer minor reactions in children as a result.
It is to be given to infants at two, three and four months, with boosters for pre-school children and teenagers.
Why has it been introduced?
The reason for the change is to do with polio. The UK is one of the last countries in the West to stop using oral polio. The oral version is better at protecting against polio imported from countries in India and Africa.
However, a campaign by the World Health Organization to eradicate polio has been so effective that the risk of catching this disease in the UK is now negligible.
For this reason, the Department of Health decided to switch to the dead or inactivated version of the vaccine, which cannot cause polio.
What are the concerns about combining the vaccines?
Some people have expressed concern that combining vaccines together overloads the immune system and increases the risk of adverse reactions.
But experts say the safety of these combinations have been thoroughly tested and they are safe and effective.
The same combination has been used in Canada for about seven years.
Researchers in the US also suggested that a mercury-based preservative used in the current vaccine could be linked to the development of autism.
However, the Department of Health has always maintained there is no evidence of such a link.
Should parents postpone vaccinating their children until the new vaccine is available?
Experts say current vaccines are extremely safe and it is vital that parents protect their children against these potentially deadly diseases.
Dr David Salisbury, vaccine expert from the Department of Health, said: "Please do not delay having your children vaccinated. Our vaccines are extremely safe. They have very, very good safety profiles.
"If you delay and you do not protect your baby against, particularly whooping cough, at a young age then you put your baby at a very high risk.
"The highest risk of children dying of whooping cough is if they catch it a young age.
"The safety issues are trivial compared with the benefit of protecting children."
How common are these diseases?
Among people of all ages in England and Wales in 2002 there were 21 reported cases of diphtheria, four of tetanus, four deaths from and 883 cases of whooping cough, 269 cases of Hib and no cases of polio.