Measles is highly contagious, but easily preventable with a vaccine.However, the numbers of measles cases sharply jumped up in Europe in 2017, according to new data released by the World Health Organization.In 2017, the disease affected 21,315 people, compared to 5,273 in 2016. Last year, 35 people died in Europe because of measles."Every new person affected by measles in Europe reminds us that unvaccinated children and adults, regardless of where they live, remain at risk of catching the disease and spreading it to others who may not be able to get vaccinated," said Zsuzsanna Jakab, WHO's Regional Director for Europe. She describes the loss of lives as a "tragedy we simply cannot accept."The WHO says that 15 countries in Europe saw outbreaks of 100 or more cases. Romania had the most, with 5,562, followed by Italy, with 5,006, and Ukraine, with 4,767."These countries have experienced a range of challenges in recent years, such as declines in overall routine immunization coverage, consistently low coverage among some marginalized groups, interruptions in vaccine supply or underperforming disease surveillance system," the WHO report stated.According to the BBC, Romania has a shortage of the vaccine. "It is also thought that the country's large Roma population, who often live in severe poverty, are at particular risk of contracting and spreading the virus," the broadcaster added.In response to the burgeoning outbreak in Italy last year, the country made vaccines mandatory for measles and a number of other diseases for school children."Kids up to 6 years old won't be accepted into nursery schools without them," reporter Christopher Livesay told NPR. "And parents sending their children to school after that age without vaccinating them first will now face fines of up to $8,380."That was controversial and sparked protest. Like many other countries, some politicians in Italy have argued against the policy by referencing widely discredited research that suggests a link between vaccines and autism.The WHO says other European countries that saw large outbreaks in 2017 are: