Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings. Dr Yvonne Doyle, London regional director for Public Health England, said: “We are seeing a concerning increase in measles cases across London which could lead to a wider outbreak in unvaccinated children and adults.“Those who have not received two doses of the vaccine in the past – or who are unsure – should speak to their GP. There’s no harm in receiving an additional dose where there is any uncertainty.“It’s crucial pregnant women have been vaccinated with MMR, as rubella in particular can cause serious complications during pregnancy.”Measles is a highly contagious infectious disease which usually starts with cold-like symptoms, fever and red, sensitive eyes. It can spread very easily and can be caught by breathing in droplets from an infected person when they cough or sneeze. Protect yourself and your family by learning more about Global Health Security A measles health alert has been issued after unvaccinated holidaymakers returning from Europe lead to a surge in cases.Public Health England have urged people to protect themselves from the viral illness after more than 250 cases have been reported since the start of the year.A further 90 laboratory tests are also underway, meaning the number could be higher. Last year, just 243 cases were reported.Health officials suspect the rise can be attributed to holidaymakers returning from the continent. In Europe, there has been a large outbreak in measles this year. It’s crucial pregnant women have been vaccinated with MMR – rubella in particular can cause serious complicationsDr Yvonne Doyle, Public Health England In rare cases, complications can include deafness, blindness and swelling of the brain, leading to brain damage, and in even more rare cases, a progressive disorder.