How a small drop in vaccinations could see measles becoming endemic again – new study

It takes just a spark to start a wildfire, and when it comes to measles, the embers are already glowing. A new modelling study published in Jama (The Journal of the American Medical Association) sounded the alarm: recent drops in childhood vaccination rates could reignite diseases that were nearly extinguished.

The researchers used a simulation to predict the effect of falling vaccination coverage for measles, rubella, polio and diphtheria. Even at current coverage, measles alone could soon infect more than 850,000 people in the US every year, leading to over 2,500 deaths annually. The study also warned how quickly the situation could get worse. A further 10 per cent drop in vaccination rates could lead to more than 11 million cases annually.

Measles is particularly concerning because of how easily it spreads. It is one of the most contagious diseases known – a single person with measles can infect between 12 and 18 others, each of whom can infect 12 to 18 more, and so on. This is much higher than for diseases such as influenza and Covid, where one person, on average, infects one to four others.

Getting a measles vaccine could save your life and also the life of a young baby and others who are unable to have it, through herd immunity (Picture: Picture by: Owen Humphreys) | PA

Diphtheria kills up to 30% of unvaccinated children

To stop measles from spreading from person to person, at least 95 per cent of the population needs to be vaccinated. But coverage is falling short – not just in the US, but worldwide. In 2024, less than 84 per cent of five-year-olds in England had received both doses of the measles, mumps and rubella (MMR) vaccine. In Scotland, 89.2 per cent of children aged five have had two MMR doses.

This matters because measles is far from harmless. About one in five children with measles need hospital care, one in 20 develop pneumonia and one in 1,000 suffer encephalitis (a brain infection that can cause seizures and deafness).

Up to three in every 1,000 children who catch measles will die.

Although measles poses the greatest immediate threat because of how contagious it is, further drops in vaccination rates could see other serious infections return. Rubella can cause devastating birth defects, polio can lead to permanent paralysis, and diphtheria is fatal in up to 30 per cent of unvaccinated children.

Before vaccines, these diseases were endemic around the world – circulating constantly, not just in outbreaks. In regions where vaccine coverage has never reached the 95 per cent target, including parts of Africa and south Asia, they remain endemic.

But in countries where vaccines had all but eliminated them, falling coverage risks undoing decades of progress. And this isn’t just hypothetical – already this year, the US has reported nearly 900 measles cases, including three deaths.

Why herd immunity is important

The MMR vaccine is extremely effective, protecting more than 97 per cent of those who receive both doses. However, some people can’t have the vaccine, including pregnant women, babies and those with a weakened immune system or serious allergy to the vaccine ingredients.

This is why herd immunity is so important: when over 95 per cent of people in a community are vaccinated, the virus can’t circulate freely, so everyone is protected – including the most vulnerable.

There are many reasons vaccination rates have fallen. Covid caused the biggest drop in global vaccination in 30 years, and many countries are still catching up. Conflict and natural disasters also contribute, with Yemen reporting over 10,000 measles cases in the past six months.

Some people choose not to vaccinate their children or themselves. This may be due to vaccine fatigue, concerns about side-effects or underestimating the risks of infection. In this respect, vaccines are victims of their own success – it can be hard to imagine the consequences of infections that have largely disappeared thanks to vaccines.

As with all medical treatments, vaccines have side-effects, but most are mild and resolve quickly, such as fever, rash and swollen glands.

Persistent misinformation

A major contributor to vaccine hesitancy is misinformation, particularly through social media. One of the most persistent myths is that the MMR vaccine is linked to autism – a claim based on falsified data in a discredited and retracted study from 1998.

Since then, multiple studies have disproved this, including a meta-analysis (a study that combines data from several studies) of over 1.25 million children that found no link between the MMR vaccine and autism.

Despite clear scientific evidence, these false claims linger, fanning the flames of doubt with real-world consequences. Indeed, the World Health Organization has listed vaccine hesitancy as one of the top ten threats to global health.

No parent takes decisions about their child’s health lightly. It’s natural to want to weigh the risks and benefits. But when vaccination rates drop, it doesn’t just put unvaccinated children at risk. It threatens those who cannot be vaccinated – including all infants under a year old, who are too young for the MMR vaccine.

Vaccination remains one of the most powerful tools we have to protect the health of all children. Diseases like measles don’t wait for conflicts to end or for trust to rebuild – they simply spread wherever they can.

We came close to extinguishing measles and other vaccine-preventable diseases, but any drop in vaccine coverage is a match to kindling. As this new research shows, it doesn’t take much for the embers to flare into a wildfire beyond our control.

Anastasia A. Theodosiou is an infectious diseases and microbiology academic clinical lecturer and Antonia Ho is a clinical senior lecturer, both at the University of Glasgow, and Chrissie Jones is an associate professor of paediatric infectious diseases at the University of Southampton

This article is republished from The Conversation under a Creative Commons licence.

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