In February 2026, a school nurse at a primary school in north London noticed something she had not seen in years: three siblings, all unvaccinated, arrived with fever, cough, and a red rash spreading across their faces. By the end of the week, six more children from the same year group had symptoms. The school, which had recorded zero measles cases as recently as 2021, was now at the centre of an outbreak that would eventually reach 17 confirmed cases. The pattern was familiar to public health officials: the children all lived in a postal code where MMR exemption rates had climbed above 5%—well past the threshold that epidemiologists say can sustain transmission.

A School Nurse’s Diary: When Measles Returns

The nurse, who asked not to be named to protect her patients’ privacy, described the scene in a log she keeps for infection incidents. “The mother said she’d heard measles was ‘not that bad’ and that she’d rather risk it than have her children receive what she called ‘unnecessary chemicals,’” the nurse wrote. “I explained that measles can cause pneumonia, encephalitis, and death, but she wasn’t convinced.” The school head teacher later told local health visitors that five years ago, the idea of a measles outbreak seemed unthinkable. “We had zero cases. Now we have a cluster, and it’s spreading because a handful of families opted out.”

The school is not alone. Across London, measles cases have been climbing since 2023, with a sharp uptick in 2025–2026. The UK Health Security Agency (UKHSA) reported roughly 1,200 confirmed cases in the capital over the 12 months to March 2026—the highest annual total since the early 2010s. Hospitalisations have concentrated in children under five and in adults with underlying conditions. One paediatric intensive care unit in north London reported an unprecedented surge in measles-related admissions during the winter of 2025, with several children requiring ventilation for measles pneumonia.

The outbreaks are geographically patchy. They cluster in areas where MMR uptake has dipped below 90%, far short of the 95% needed for herd immunity. In some affluent postal codes—parts of Kensington, Richmond, and Camden—exemption rates for non-medical reasons exceed 5%. Public health teams have struggled to access independent schools, where vaccination rates can be as low as 75%. “We have a paradox,” says Dr. Helen Bedford, a professor of child health at University College London. “Wealthy, well-educated parents are choosing not to vaccinate, and their children are becoming vectors for a disease that disproportionately harms poorer kids who may have missed doses for access reasons.”

How Vaccine Exemption Clusters Form

Vaccine exemptions in the UK are not as simple as a single form. Parents who wish to opt out of the MMR vaccine for non-medical reasons must discuss it with a health visitor or GP, but there is no mandatory counselling or waiting period. In practice, many parents share exemption paperwork through private online forums and home-schooling networks. “It spreads like a rumour through these groups,” says Dr. Heidi Larson, director of the Vaccine Confidence Project at the London School of Hygiene & Tropical Medicine. “When a parent sees three other families in their WhatsApp group who have successfully exempted, the perceived risk of the vaccine outweighs the perceived risk of the disease.”

The phenomenon is particularly pronounced in private schools, where parental pressure on head teachers can be intense. Some independent schools have vaccination rates as low as 75%, according to UKHSA surveillance data shared with local authorities. In one prominent private school in Richmond, the exemption rate for MMR reached 9% in 2024—nearly twice the borough average. School leaders are often reluctant to enforce vaccination policies for fear of losing fee-paying families. “We’re caught between public health and parental choice,” one head teacher told a local health board meeting in 2025, according to minutes obtained by a community health group.

Philosopher Julian Savulescu of the University of Oxford has described non-medical exemptions as a form of “free-riding” on herd immunity. “Parents who exempt are relying on everyone else’s children to be vaccinated to protect their own,” he wrote in a 2024 commentary. “But when enough people free-ride, the herd immunity collapses.” The ethical argument has gained traction in public health circles, though it remains controversial. Some parents argue that they have a right to make medical decisions for their children, and that the MMR vaccine carries a small risk of adverse events, such as febrile seizures—a risk that is far lower than the complications of measles itself.

The UK does not track exemption rates nationally in real time, but local surveys suggest that in some London boroughs, non-medical exemptions account for 60–70% of all MMR exemptions. Medical exemptions—for children with genuine contraindications, such as severe immunodeficiency—are rare, affecting roughly 0.2% of children. The clustering effect is amplified by geography: when several exempt families live in the same catchment area, the local vaccination rate can fall below the herd immunity threshold, creating a pocket of susceptibility that an imported case can ignite.

The Outbreak Curve: London 2025–2026

The current wave of measles in London began in earnest in late 2024, when UKHSA detected a cluster of cases among teenagers at a secondary school in Camden. By mid-2025, the outbreak had spread to multiple boroughs, with a total of roughly 1,200 confirmed cases by March 2026. The majority of cases—about 70%—occurred in children who had not received any dose of the MMR vaccine. An additional 15% occurred in children who had received only one dose, which is less effective than the recommended two-dose schedule. Breakthrough infections in fully vaccinated individuals were rare, accounting for less than 5% of cases, and were typically mild.

Hospitalisations have been concentrated in the under-five age group, where measles can cause severe dehydration, pneumonia, and encephalitis—a brain inflammation that can lead to permanent neurological damage. UKHSA documented at least 12 cases of measles encephalitis during the outbreak, all in unvaccinated children. One paediatric intensive care unit in north London was so overwhelmed that it temporarily diverted non-measles respiratory cases to neighbouring hospitals. No deaths had been reported as of mid-2026, but officials warned that the risk remains, particularly if the outbreak spreads to infants too young to be vaccinated.

The virus's basic reproduction number (R0) is estimated at 12–18 in an unimmunised population, meaning each infected person can infect 12 to 18 others. In a school setting with low vaccination coverage, an outbreak can expand exponentially within weeks. “Measles can linger in the air for up to two hours after an infected person leaves a room, and it remains infectious on surfaces for several hours,” notes Dr. Mary Ramsay, director of immunisation at UKHSA. “In a school with 30% unvaccinated children, the virus can spread faster than we can trace contacts.”

The outbreak has also affected adults, particularly those born between 1970 and 1990 who may have received only one dose of the MMR vaccine or who were too old to be vaccinated during the catch-up campaigns of the early 2000s. Among the 1,200 cases, roughly 15% were in adults aged 20–50, several of whom required hospitalisation for pneumonia. A 2025 modelling study in The Lancet estimated that if London’s MMR coverage remains below 90%, the city could see 5,000–10,000 cases over the next two years, with dozens of severe complications.

Why the Geography Matters

The geography of vaccine exemptions in London is striking. Affluent boroughs such as Kensington and Chelsea, Richmond upon Thames, and Camden have some of the lowest MMR uptake rates in the city, despite having the highest average household incomes. In Kensington, MMR coverage for two doses by age five hovered around 84% in 2024, compared with 92% in more deprived boroughs like Newham. The pattern is not unique to London: similar clusters have been documented in wealthy suburbs of Los Angeles, Sydney, and Berlin. But in London, the concentration of private schools in these areas creates a multiplier effect.

Public health teams face a practical challenge: they have limited authority to enter independent schools. Unlike state schools, which are required to share vaccination data with local health authorities, private schools are not always cooperative. “We’ve had head teachers tell us they don’t want to ‘stigmatise’ exempt families,” says a public health nurse who works in north London. “We can offer catch-up clinics, but we can’t mandate them.” The result is that children in private schools may be less likely to be vaccinated than their peers in state schools—a reversal of the pattern seen in previous decades, when private school children had higher vaccination rates due to better access.

The inequality has a downstream effect. When measles enters a school with low vaccination coverage, it spreads to the surrounding community. Children from poorer families who attend state schools may be exposed to the virus through shared activities—sports leagues, after-school clubs, religious gatherings. “The rich kids who aren’t vaccinated become a source of infection for the poor kids who missed their shots because their parents couldn’t take time off work,” says Dr. Bedford. A 2024 analysis by the Health Foundation (available at health.org.uk) found that measles hospitalisation rates in London were three times higher in the most deprived quintile than in the least deprived, even though vaccination rates were lower in affluent areas.

The geography also matters for outbreak control. When an outbreak is confined to a small, wealthy neighbourhood, public health resources can be targeted. But when exemptions are scattered across multiple boroughs, contact tracing becomes difficult. UKHSA has deployed mobile vaccination units to affected areas, but uptake has been modest. “We’re fighting a fire that keeps igniting in new places,” says a UKHSA epidemiologist. “Every time we contain one cluster, another pops up in a different private school.”

The Evidence on Exemption Impact

The link between non-medical exemptions and measles outbreaks is well established. A 2024 modelling study in The Lancet Infectious Diseases estimated that a 5% exemption rate in a school increases the risk of an outbreak by roughly threefold, compared with a school where exemptions are below 1%. The study, which used data from London and the South East, projected that reducing exemption rates to below 2% would prevent 60% of potential outbreaks. Similarly, a 2020 study by the US Centers for Disease Control and Prevention (CDC) found that non-medical exemptions were geographically clustered and strongly associated with pertussis outbreaks in California.

UK-specific data reinforce the pattern. During the 2025–2026 outbreak, UKHSA reported that 70% of confirmed measles cases occurred in children who had received zero doses of the MMR vaccine. Of the remaining cases, most had received only one dose. The proportion of cases among fully vaccinated individuals was consistent with the small fraction of the population that does not mount a sufficient immune response—roughly 2–5% after two doses. “The vaccine works,” says Dr. Ramsay. “The problem is not vaccine failure; it’s vaccine refusal.”

Critics of mandatory vaccination argue that exemptions are not the sole driver of outbreaks. Some point to gaps in the routine immunisation schedule, such as missed appointments due to pandemic disruptions. In 2020–2021, MMR coverage in England fell to 85% for two doses, the lowest level in a decade, as lockdowns and school closures interrupted vaccination programmes. Recovery has been slow: as of 2024, coverage had rebounded to only 89% nationally, with London lagging at 86%. “We can’t blame exemptions alone,” says Dr. Larson. “We have a systems problem—too many children are falling through the cracks regardless of parental choice.”

Nevertheless, the clustering of exemptions in schools is a distinct and modifiable risk factor. A 2023 study by Ward et al. in the journal Vaccine examined exemption rates in English schools and found that schools with exemption rates above 5% were 10 times more likely to experience a measles outbreak than schools with rates below 1%. The study also noted that exemption clusters were highly predictable: they correlated with the presence of private schools, high household income, and a high proportion of parents with postgraduate degrees—a demographic that, paradoxically, tends to have high health literacy but also high exposure to anti-vaccine content online.

What Schools and Parents Can Do Now

In response to the outbreaks, some London boroughs have introduced catch-up clinics in school halls during term time, offering the MMR vaccine to children who missed doses. The approach has shown promise in state schools, where uptake increased by 10–15 percentage points after a clinic was held. In private schools, however, participation has been lower. “Parents have to opt in, and many don’t,” says a school nurse who organised a clinic in a private school in 2025. “We had 20 slots and only 8 filled.”

Mandatory vaccination for school entry is a debated policy. Italy, France, and Australia have all introduced compulsory MMR vaccination for school attendance, with notable success. Italy’s coverage rose from 85% to 94% within two years of its 2017 mandate, and France’s 2018 law brought coverage above 95% for the first time in a decade. In the UK, the government has so far resisted a mandate, citing concerns about parental backlash and logistical challenges. But the Royal College of Paediatrics and Child Health has called for a “no jab, no school” policy for measles, at least in outbreak areas.

Peer-to-peer vaccine education programmes have shown some success in shifting attitudes. A pilot programme in Camden trained parent volunteers to discuss vaccine safety with hesitant families in their own social networks. The programme, which ran from 2023 to 2025, was associated with a 7% increase in MMR uptake among children of participating families, compared with a control group. “Parents trust other parents more than they trust doctors,” says Dr. Larson. “But it’s slow work, and it can’t keep up with the speed of an outbreak.”

Some boroughs have introduced exemption review panels, where parents who seek non-medical exemptions must meet with a public health nurse to discuss the risks and benefits of vaccination. The panels do not have the power to deny exemptions, but they have been associated with a modest reduction in exemption rates—roughly 10% in the first year. “It’s not a silver bullet, but it forces a conversation,” says a public health official in Richmond. “Some parents change their minds when they hear about the child in the next borough who nearly died from measles encephalitis.”

The Fragile Wall of Herd Immunity

London’s overall MMR coverage for two doses by age five hovers near 86%, well below the 95% threshold that the World Health Organization (WHO) considers necessary to prevent sustained measles transmission. The WHO warned in 2024 that the UK, along with several other European countries, was facing a “perfect storm” for measles resurgence, driven by pandemic-era vaccination gaps and rising vaccine hesitancy. Global measles deaths rose by 43% from 2021 to 2022, according to WHO estimates, with large outbreaks in India, Nigeria, and Pakistan. The UK lost its measles-free status in 2018 and has not regained it.

The fragility of herd immunity means that a single imported case can ignite a cluster. In 2025, UKHSA traced the source of the Camden outbreak to a teenager who had travelled to Romania, where a large measles outbreak was ongoing. Within three months, the virus had spread to six schools across three boroughs. “We are one flight away from an epidemic at any time,” says Dr. Ramsay. “The wall of herd immunity is only as strong as its weakest point.”

Efforts to strengthen that wall face headwinds. Anti-vaccine messaging on social media continues to erode confidence, particularly among younger parents who may not remember the pre-vaccine era when measles caused hundreds of deaths each year in the UK. A 2025 survey by the Vaccine Confidence Project found that 12% of UK parents with children under five believed that vaccines cause more harm than good—up from 7% in 2020. The trend is most pronounced in affluent areas, where parents are more likely to encounter alternative health influencers online.

Looking ahead, the return of measles to London schools forces a difficult trade-off: how to balance parental autonomy with the collective right to protection from a preventable disease. Some experts argue that the current approach—education and voluntary catch-up—is insufficient in the face of rising exemption rates. Others warn that mandates could backfire by alienating hesitant parents. What is clear is that without a sustained effort to close the vaccination gap, London will remain vulnerable to outbreaks that disproportionately affect the most vulnerable. As one public health nurse put it: “We can’t assume that because we’ve seen the back of a disease, it won’t come back. It will, if we let our guard down.”

This article is for informational purposes only and does not constitute medical advice. Readers should consult their healthcare provider for vaccination recommendations.