Measles cases are likely to spread rapidly unless more people are vaccinated, the UK Health Security Agency says.
More than four million parents and carers, as well as many young adults, are being contacted because they, or their children, have missed out on one, or both, doses of the measles, mumps, rubella (MMR) vaccine.
Measles is a highly contagious disease which is spread by coughs and sneezes.
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 to the rest of the body.
It can be harder to see on brown and black skin.
Measles normally clears up within seven to 10 days. However, complications can include 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. Over a 22 year period, between 2000-2022, 23 children and adults died in England and Wales as a result of measles or related infections.
You can catch measles at any age.
If you catch it while pregnant, the disease can lead to stillbirth, miscarriage or babies being born small.
The NHS urges adults to ensure they have had both doses of the MMR vaccine before starting a family.
It is possible, but highly unlikely.
The body builds up immunity to the disease after catching it.
Measles vaccinations were introduced in the UK in 1968. The current two-dose MMR vaccine was introduced 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 while the second jab is administered around three years and four months.
However, adults and children can have be vaccinated at any point by their GP.
Pop-up clinics are being set up at schools in areas where cases have risen.
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 side effects are mild.
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.
Researcher Andrew Wakefield wrongly claimed the two were connected in 1998.
His work was later dismissed, and Mr Wakefield was struck off by the General Medical Council in 2010.
There were 1,603 suspected cases of measles in England and Wales in 2023, according to the UK Health Security Agency (UKHSA) – a sharp rise from 735 cases in 2022 and 360 in 2021.
The West Midlands, particularly Birmingham, has seen the most cases in recent months – more than 200 at the latest count.
There have also been smaller outbreaks in parts of London, where only 74% of five-year-olds have had two MMR doses. In a few areas, such as Hackney in east London, nearly half of children under five are not fully vaccinated.
There are also small clusters of cases in other areas of England.
The World Health Organization (WHO) says there was an “alarming” 30-fold increase in measles cases across Europe in 2023.
More than 30,000 people were infected, compared to 941 during the whole of 2022.
The number of young primary school children who have had both doses of the MMR vaccine is below WHO targets.
Approximately 85% of children in 2022-23 had received two MMR doses by their fifth birthday, the lowest level since 2010-11. The recommended figure is 95%.
In some cities, such as Liverpool, Manchester, Birmingham and Nottingham, only 75% of five-year-olds are fully vaccinated, NHS figures show.
It means more than 3.4 million children in England aged under 16 are unprotected.
The WHO said vaccination rates have also fallen across Europe, leaving more than 1.8 million children at risk.
Child health experts say some parents underestimated the seriousness of measles because 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. Some young adults who are not vaccinated today missed out when they were children because those fears were prevalent among new parents at the time.
The NHS advises patients to:
You should go to A&E or phone 999 if you or your child:
Pregnant women or those with a weakened immune system should seek urgent medical advice after contact with someone with measles.
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