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What is behind the spate of recent measles outbreaks?
The UKHSA declared a national measles incident in January 2024 amid a surge in cases -

Over the past 10 years, we have seen multiple outbreaks of measles, a high contagious yet easily prevented infection.1 For two years in 2026 and 2017, the UK had achieved endemic elimination only for the measles virus to be re-established, at a time when the whole of Europe was experiencing large epidemics. The UK then lost its WHO measles elimination status in 2019. Measles activity almost disappeared during the COVID-19 pandemic due to the implementation of travel restrictions and non-pharmaceutical interventions (face masks, social distancing etc). Sadly by 2023, the incidence increased again globally, including the UK.

January 2024 saw the UK Health Security Agency (UKHSA) declare a national incident amid a surge in cases, with a disproportionately high rate in the West Midlands.2 The vast majority of cases are in children aged under 10 years. This is interesting as former outbreaks – for example 2018 – had mostly been in young adults over the age of 15 years.3 These previous outbreaks were mostly associated with travel to and from areas of measles outbreaks in Europe and in young people and adults who had missed out on the MMR vaccine when they were younger.

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Young people born between 1998 and 2004 (aged 19 to 25 years in 2023) are the most susceptible (the so-called ‘Wakefield cohort’) and the burden of measles also falls disproportionately on under-vaccinated communities such as the Charedi Orthodox Jewish community, the traveller community, Steiner (anthroposophic) community and recent migrants.4

Our current national incident has been driven by a rise in cases over 2023 and a huge drop in MMR vaccine coverage. Current MMR coverage in the routine childhood immunisation programme is the lowest it has been in a decade with about 10% of children not protected from measles by the time they are ready to start school.5

The latest available published data is for the quarter July-September 2023, where 89.9% of UK children had their first dose of MMR by 2 years of age whilst 92.7% of children aged 5 years had their first dose of MMR and 84.% had competed their two doses.6 There is variation between countries and between regions, with London traditionally being the lowest region for vaccine uptake (85.6% of London resident 5 year olds had one dose MMR and only 72.8% had both doses). Indeed, UKHSA had warned in July 2023 that London was in danger of a major measles outbreak that could result in 40,000-160,000 cases, dozens of deaths, and thousands of hospitalisations.7 With measles cases continually rising, what can we do to stop the spread?

What is measles?

Measles is an extremely infectious virus that is transmitted by respiratory route mostly by droplet spread or direct contact with nasal or throat secretions of infected people (i.e. airborne transmission). Incubation is typically around 10-12 days from exposure to onset of symptoms. The period of infectiousness generally starts from 4 days before the rash and lasts up to 4 full days after the onset of the rash. Spending more than 15 minutes in direct contact with someone infected with measles is enough to transmit the virus. Measles has a high basic reproduction number (R0). It is estimated that around 12-18 individuals would be infected from a single case in a totally susceptible population.8 This is much higher than influenza (R0 =2-3) or Delta variant of SARS-CoV-2 virus (R0 = 5-8).9

As measles has been around for centuries, all populations have had exposure to measles. However, R0 is important as it determines the herd immunity threshold and therefore the immunisation coverage required to achieve elimination of an infectious disease. As R0 increases, a higher immunisation coverage is required to achieve herd immunity.

The World Health Organisation (WHO) recommended threshold is 95% uptake of at least one measles containing vaccine (MCV) to provide the herd immunity needed to prevent outbreaks. WHO modelling has shown that incidence of measles drops to a rate of 0.9 per 100,000 a year when coverage of one dose of a measles containing vaccine is between 90 and 100%.10

Modelling also shows that for each 1% increase in 1st dose MCV, there is 2% decrease in measles incidence that same year and following years.10 Because measles is so contagious, it is difficult for countries to achieve measles elimination. Subpopulations who have not received a measles vaccine or constantly miss out on vaccines (e.g. travelling communities) can trigger localized measles outbreaks. Quite often, these outbreaks can be contained within these groups. However if we are seeing declining uptake of the routine childhood immunisation programme, we are not only seeing the age distribution of measles shift to young children but we are also at risk of widespread transmission in the population.

The importance of MMR vaccine coverage

Measles is a vaccine-preventable disease as lifelong immunity follows vaccination. It has been found that 100% of children who received first dose of MMR at 14-18 months of age and second dose MMR at 4-6 years of age had detectable antibodies 20 years after vaccination.11 The MMR vaccine is very effective. Vaccination of one dose of MMR is at least 95% effective preventing clinical measles and 99% after 2 doses. No vaccine offers 100% protection. There can be some individuals who may get infected despite vaccination. This is due to primary vaccine failure (an individual fails to make an initial immunological response to the vaccine) or secondary vaccine failure (protection has waned over time). This is one of the reasons why two doses of MMR are recommended.

With the large number of cases being in the under 10s, you can see the disruption COVID-19 pandemic brought to healthcare services. There are children who have missed out on their MMR whether it be their first dose at 12/13 months or their second dose before school entry during a pandemic where there were restrictions on attending primary care services. This was despite the many endeavours to continue immunisations – for example drive-through vaccination services.12 The COVID-19 pandemic has had a negative impact on coverage rates for several vaccines across the globe. Factors contributing to low vaccine coverage included fear of being exposed to the virus at healthcare facilities, restriction on city-wide movements, shortage of workers, and diversion of resources from child health to address the pandemic.13 Vaccine fatigue has also been reported as negatively impacting vaccination uptake.14  We now have children who need to catch up on these missed vaccinations as well as prioritising the vaccination of the current 0-5 year olds on the routine childhood immunisation schedule.

What can we do?

Measles is a threat to children’s health and there needs to remain a focus on ensuring all children are invited and reminded for their two doses of MMR on the routine childhood immunisation schedule. Supplementary immunisation campaigns are also needed to get those children who missed out on their MMR invited for vaccination. Sometimes there is an assumption that these children missed out due to parents being against MMR or being vaccine hesitant, but many will have simply missed out due to the COVID pandemic. These children can be identified on GP systems. Ideally, local partnerships can utilise other family engagement with the system to flag MMR – for example: having an MMR check at 1 year development check with health visitors; at the 2 ½ year development check; in early year settings (nurseries, preschools); MMR checks by school aged vaccination services when providing other vaccines. Some years ago, I was involved in creating a quick question for all healthcare staff to ask patients about when they had their MMR. At that time, there was reluctance in the system to ‘pry’. Following a pandemic, when we are used to asking about someone’s COVID status, it may be time to revisit this. Everyone is entitled to two doses of MMR free on the NHS. Measles cases are dramatically increasing daily. Our best defence remains vaccination.  


Catherine Heffernan is Consultant in Public Health and a Fellow of the Faculty of Public Health


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14. Su Z, et al. 2022. Mind the “Vaccine Fatigue”. Front Immunol. Mar 10;13:839433.