According to the NHS, initial symptoms can include aches and pains, a fever and a runny nose.
More than 120 cases of measles have been confirmed in the United Kingdom, with the outbreak affecting five areas in particular.
Less than one in 1,000 measles cases result in more serious issues involving the nervous system, such as inflammation of the brain, a quarter of those can result in brain damage.
PHE says cases in England appear to be stabilising.
More than 120 cases of measles have now been confirmed in outbreaks affecting five areas of England, while those travelling to Romania, Italy and Germany without receiving two doses of the MMR vaccine are particularly at risk.
Measles is a very infectious, serious illness that, in rare cases, can be fatal.
However, complications can develop in some cases of measles and if you feel your health is getting worse, seek medical help.
While the outbreak was first reported in November as spreading through Leeds and Liverpool, there are now confirmed cases in Sussex, West Midlands, Surrey, Greater Manchester, Merseyside and West Yorkshire, reports The Sun.
Measles usually lasts between seven to 10 days and most symptoms can be eased at home.
However, measles can lead to serious and potentially life-threatening complications in some people.
Dr Ramsay said the overall risk to people in the United Kingdom is low.
The vaccine against measles, mumps and rubella (MMR) is offered to children when they are one years old and parents are then invited to take children for a second injection, sometimes known as the "pre-school booster" at 3 years and 4 months of age.
This means the number of cases in the United Kingdom across a period of at least three years was low enough to prevent the disease spreading among the general population.
Experts are urging parents to immunise their children.
Adults and older children can be vaccinated at any age if they haven't been fully vaccinated before.
We will continue to see imported measles cases in the United Kingdom and anyone who has not had two doses of the MMR vaccine can catch it.
Children and young adults who missed out on their MMR vaccine in the past or are unsure if they had two doses should their GP practice to catch-up.
Dr Morrison added: "Rather than trying to avoid the complications once you've got measles, it's best to vaccinate against it".
PHE says local health protection teams are working with the NHS and local councils to raise awareness of the outbreaks in England and on the continent.
The overall risk in the United Kingdom is still low, but outbreaks can happen any time.