Fourteen years ago we believed that measles could be eradicated through vaccination.¹

By the millennium, indigenous measles had all but disappeared from the UK,^2-3 and in 2002 the disease was declared eliminated in the Americas.⁴ In 2008 some believed that measles might be eradicated altogether by 2015.⁵

Yet recently measles cases have increased dramatically. England and Wales have seen a ten-fold increase in measles: 334 laboratory confirmed cases were reported to the HPA between January and April 2011, compared with 33 for the same period last year.^6-7 Most of the cases in the UK have been in unvaccinated children and young adults, many of whom have acquired the disease abroad or in small clusters in university, school, or family settings.

Is this the start of a prolonged pandemic or just a temporary blip? Measles is one of the most infectious diseases known.² In a naïve population each case will initially infect about 15 other people. Transmission, by respiratory droplet spread, has been documented between people attending the same event in an outdoor stadium or using the same consulting room up to an hour apart. Before the introduction of vaccination nearly everyone caught measles as children.

When a high enough proportion of the population is immune, there is little likelihood of a case meeting somebody who is susceptible, so the disease is not sustained in the population. Following the catch-up vaccination programme of all school-aged children in the mid-nineties,⁸ population immunity was easily achieved, as so many people were already immune.

But sustaining population immunity is harder: at least 95% of the population must be immune. The rise in measles cases is due to failure to achieve or sustain the high levels of vaccination required.

In the first decade of this century MMR vaccination rates in the UK fell to a level which was too low to maintain herd immunity. All is not lost. Even during the height of the vaccine scare caused by Wakefield's fraudulent ‘research', a majority of parents were willing for their children to be vaccinated.

Everybody born after 1970 (those born earlier are likely to have natural immunity) should have [had] two qualifying doses of measles-containing vaccine such as MMR. The first dose must be given after the age of one year and the second given at least four weeks later (three months later if given before the age of 18 months). Many of the children who remain unvaccinated or incompletely vaccinated could be vaccinated: susceptible children will otherwise become susceptible adults - until they catch measles.

GPs can do a great deal to improve uptake, by using their systems to flag up all patients who are not known to be fully vaccinated, and ensuring that whenever they have contact with the practice, they are offered the vaccines they are overdue. It's never too late to get vaccinated. Good information systems help. Children who have missed appointments should be offered further appointments, and all patients should be offered vaccination opportunistically when they attend for other reasons.⁹ If this is done rigorously many more children can be vaccinated, leaving only a few others whose parents are willing for them to be vaccinated: in some areas domiciliary vaccination is offered to these children, with good effect - the numbers are relatively small. Confidence in vaccination is improving, with almost 90% of children vaccinated by their second birthday.

Such actions, combined with other initiatives such as opportunistic vaccination in other healthcare settings and public information about the benefits of MMR vaccination (such as the Health Protection Agency's recent advice about MMR prior to overseas travel7) should enable us to raise vaccination levels until we can, once again, achieve and sustain population immunity.

Acknowledgements

The author's views do not necessarily reflect those of the HPA. The author would like to thank Dr Mary Ramsay at the HPA Centre for Infections for her input.