A young child has died at Liverpool's Alder Hey Hospital after contracting measles, raising concerns about the spread of the disease.
Cases have been rising in the UK and around the world, with more than 500 reported since January in England alone.
The increase is being blamed on the poor uptake of the MMR (measles, mumps and rubella) vaccine.
Measles is a highly contagious disease which is spread by coughs and sneezes.
Common symptoms include:
Small white spots may appear inside the mouth.
A blotchy red or brown rash usually appears after a few days, typically on the face and behind the ears, before spreading.
The rash can be harder to see on brown and black skin.
Measles normally clears up within seven to 10 days. However, it can lead to pneumonia, meningitis, blindness and seizures.
Babies and young children, pregnant women and those with a weakened immune system are at increased risk.
Measles can be fatal, but this is rare.
Between 2000-2023, 26 children and adults died in England and Wales from measles or related infections.
Before the latest case in Liverpool, the last child to die as a result of measles complications was 10-year-old Renae Archer, in 2023.
You can catch measles at any age. It is possible - but highly unlikely - to catch it twice as the body builds up immunity to the disease after being infected.
Getting it while pregnant can lead to stillbirth, miscarriage or babies being born small.
The NHS advises adults to ensure they have had both doses of the MMR vaccine before starting a family.
There were 2,911 confirmed cases of measles in England in 2024, which is the highest annual total since 2012.
According to the UK Health Security Agency (UKHSA), this started with an outbreak in Birmingham, which was then overtaken by a surge of cases in London.
More than 60% of the 2024 cases were in children aged 10 and under.
As at 3 July, there had been 529 reported cases in England in 2025, with 68% occurring in children under 10:
Alder Hey Hospital has treated 17 children for measles since June.
The World Health Organization (WHO) and Unicef have warned that the number of measles cases in the European region doubled to 127,350 in 2024 - the highest level in 25 years.
A report from the two organisations said children under the age of five accounted for more than 40% of the cases reported in Europe and central Asia.
As at 4 July, there were nearly 1,300 confirmed measles cases in the US - a 33-year high.
More than nine in 10 of those affected (92%) were either unvaccinated or did not know their vaccination status.
Texas is the the worst-hit state with more than 700 cases. Kansas and New Mexico have also had outbreaks.
At least three people have died and 155 others have been hospitalised.
The number of young primary school children in the UK who have had both recommended doses of the MMR vaccine is below WHO targets.
NHS figures for 2023-2024 show that 84.5% of children across the UK had received two MMR doses by their fifth birthday. The recommended figure is 95%.
Across England, London had the lowest take-up at 73.3%, followed by the West Midlands at 83.1% and the North West at 84.5%.
The WHO said vaccination rates have also fallen across Europe, leaving millions of children at risk.
Child health experts say some parents underestimate the seriousness of measles because the success of the vaccine programme meant it had largely been eradicated.
In addition, many routine health appointments were missed during the Covid pandemic.
There are also still people who wrongly believe the MMR jab is linked to autism. Researcher Andrew Wakefield falsely claimed the two were connected in 1998.
His work was later dismissed, and Wakefield was struck off by the General Medical Council in 2010, but fears about the jab persisted despite being disproven.
The outbreak in the US follows a sharp rise in anti-vaccine sentiment.
The current Health Secretary Robert F Kennedy Jr previously spread misinformation about childhood vaccinations and had minimised the danger of measles. He also promoted unproven treatments like cod liver oil.
As cases have grown, he has backtracked on the MMR vaccine, writing in a post on X that it was "the most effective way to prevent the spread of measles".
Public health experts have warned that the US will lose measles elimination status if the disease continues to spread at the current rate for more than 12 months.
The first measles vaccinations were introduced in the UK in 1968. The current two-dose MMR vaccine started in 1996 and is very effective.
After both MMR doses, 99% of people are protected against measles and rubella and 88% are protected against mumps.
The first MMR dose is usually given at 12 months old, while the second jab is administered at about three years and four months, before children start primary school.
However, adults and children can have the MMR jab at any point via their GP.
People who do not eat pork products can request an alternative jab called Priorix.
If the MMR is not suitable, someone at immediate risk of catching measles can have a treatment called human normal immunoglobulin (HNIG).
Most MMR side effects are mild but the injection site can be red, sore and swollen for a few days.
Babies and young children may develop a high temperature for up to 72 hours.
There is no evidence linking the MMR vaccine with autism.