How the MMR vaccine works

The West Midlands is in the midst of a measles outbreak, with health officials warning of the "real risk" that a decline in MMR vaccine coverage could see the virus spread rapidly nationwide.

According to the UK Health Security Agency (UKHSA), three-quarters of the 347 cases in England between 1 October and 23 January were in the West Midlands. London accounted for 13% of cases, while 7% were in Yorkshire and the Humber.

The majority of those cases (67%) were in children under the age of 10, while 24% have been in young people and adults over the age of 15.

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Dr Vanessa Saliba, a consultant epidemiologist at UKHSA, told the i news site that the ongoing outbreak in the West Midlands "remains a concern". 

"MMR vaccine coverage has been falling for the last decade," she said, "with 1 out of 10 children starting school in England not protected and so there is a real risk that this outbreak could spread to other towns and cities."

How common is measles?

There were around 1,600 suspected cases of measles in England and Wales in 2023, according to UKHSA – a significant rise from 725 cases in 2022, and 360 in 2021.

Europe is also seeing a rise in measles cases. The World Health Organization (WHO) has warned of an "alarming" 30-fold increase in measles cases across the continent in 2023, said The Guardian, with more than 30,000 people infected, compared to 941 in 2022.

Why are we seeing outbreaks?

Falling MMR vaccination rates are contributing to the spread of the disease. In Birmingham, which is seeing the worst of the current outbreak, the vaccination rate for under 5s is 75%, when "ideally it should be 95%", said the BBC.

In other major cities in the UK, such as Liverpool, Manchester and Nottingham, the vaccination rate is similarly low among the under 5s. In London, only 74% of five-year-olds have had two MMR doses. In some boroughs, such as Hackney, nearly half of children under five are not fully vaccinated. 

Across the UK, the number of young primary school children who have had both doses of the MMR vaccine is below WHO targets. Only 85% of children in 2022-23 had received two MMR doses by their fifth birthday, the lowest level since 2010-11, said the BBC.

According to NHS figures, 3.4 million children under the age of 16 are not fully vaccinated with MMR. 

What is the MMR vaccine and how does it work?

The MMR vaccine gives protection against measles, mumps and rubella, three serious but – thanks to vaccines – preventable diseases. 

Before the introduction of the MMR vaccines in the UK, in 1988, these illnesses were extremely common and for many led to long-term health problems or, in some cases, death. 

In order to be fully vaccinated against measles, mumps and rubella, children receive two doses of the MMR vaccine. In the UK, the first dose is given at about a year old. Another booster dose is given to children at around three years and four months. 

As the UKHSA explains, the MMR is a "live" vaccine that works through the body’s immune response. Once injected with the vaccine, the immune system responds by producing cells that "recognise" each of the three viruses. If the vaccinated person come into contact with any of these diseases in the future, these cells will "wake up" and begin to produce antibodies that protect you from illness. 

The vaccine is extremely effective. According to Oxford University, "two doses are 96% effective against measles, around 86% effective against mumps, and 89% effective against rubella". 

Why have vaccination rates fallen?

Vaccination rates have been falling in the UK since the 1990s, with concerns over the safety and effectiveness of vaccines being one contributing factor. 

So-called "vaccine hesitancy" increased dramatically both in the UK and across the world after a now discredited study by Andrew Wakefield was published in 1998, linking the MMR vaccine to autism. 

Wakefield’s study was retracted by the journal that published it, and Wakefield was struck off the General Medical Council register in 2010. Nevertheless, its impact on parental trust in vaccination has been "massive", wrote Professor Devi Sridhar, chair of global public health at the University of Edinburgh, in The Guardian.

With health services "increasingly strained", access to vaccination clinics for many parents and carers has become more challenging, with many struggling to get their children vaccinated "even when they understand the value" of it. 

And because measles, mumps and rubella have, for many years, been near total elimination (due to the effectiveness of the vaccine and the success of public health initiatives), Sridhar added, a certain amount of "parental complacency" has crept in.