Prime Minister Boris Johnson says action needs to be taken to stop the spread of measles in the UK.
Britain has lost its measles-free status - three years after the virus was eliminated.
In the first three months of this year, 231 cases were confirmed across the country.
Measles is a viral illness. It might begin with a headache, or seem like a cold or the flu.
Eventually it causes a red-brown rash to appear on the skin and can make your tummy hurt and give you diarrhoea.
Symptoms usually last about two weeks, but in rare cases it can lead to further problems for kids who catch the disease.
Nobody likes injections, but doctors and the government say they are really important to stop you from getting ill.
The injection to protect you from measles - also known as a vaccine - is called the MMR jab.
The vaccine protects against three different illnesses - measles, mumps and rubella.
To be properly vaccinated, you need an injection twice.
Normally babies are given their first MMR injection just before their first birthday. The second injection comes just before you start school for the first time.
The NHS says that since the MMR vaccine was introduced 30 years ago, it is very rare for children in the UK to develop these serious conditions. But to be sure you're safe, doctors say it's really important to have the injections.
The recent spread of the measles in the UK is thought to be because fewer people have been vaccinated.
Currently, only 87.2% of children have had their second injection.
Prime Minister Boris Johnson wants that figure to increase to 95% and has written to all doctors asking them to make sure children and young people have had both MMR jabs.
Child health experts say there are a number of reasons why people aren't getting vaccinated, including fake information about the injections having bad side-effects. This has worried some adults, who thought the injections were unsafe.
The prime minister said: "From reassuring parents about the safety of vaccines to making sure people are attending follow-up appointments, we can and must do more to halt the spread of infectious, treatable disease in modern-day Britain".
The government says it will also improve the advice on the NHS website, as well as targeting areas where fewer people are getting vaccinated.
Social media companies will be asked to look at how they can promote accurate information about the injections too.
Health Secretary Matt Hancock recently said he wouldn't rule out making it the law that everyone had to have their MMR injections, saying: "It's easy to forget how devastating measles can be precisely because vaccines are so effective at preventing it in the first place."
In 2015, lots of teenagers in the UK were given catch-up measles injections after missing their second jabs as children. It's thought this helped to lower the number of people getting ill with measles at the time.
Measles has caused a lot of problems in countries where children aren't properly vaccinated.
In areas where there is not a lot of money or in remote places, it can be hard for kids to get the injections they need. That means they might catch conditions like measles and become very ill.
However, even in Europe, measles is still really common in countries such as France, Germany and Italy.
The World Health Organization says that measles cases nearly tripled globally between January and July this year, compared to the same time period last year.
So far this year, there have been 364,808 measles cases reported around the world in 2019.