Europe had a record number of measles cases previous year, in part due to a growing number of pockets where parents are refusing to vaccinate their children, the World Health Organisation (WHO) says.
Also fueling the spread of measles are adults who received only one shot of vaccine, instead of the two routinely given today, and may now need booster shots, Jankovic said. Measles cases in the Philippine capital region also surged 10 times at the start of the year, as the government failed to hit its immunization target in 2018.
"All of our cases match this strain", the Washington State Department of Health said in an email.
Ukraine recorded the highest number of measles cases in Europe in 2018, at 53,218.
That helps explain why public health officials get so concerned when outbreaks occur, which they have been with increasing frequency in recent years.
Melnick added that while 78% of schoolchildren in Clark County are vaccinated, some schools have much lower rates.
One explanation for the reversal of the previous trend of measles infection rates falling is the influence of anti-vaccine campaigners who have sought to discourage parents from immunising their children in the face of overwhelming scientific evidence that vaccines are both effective and safe.
The case prompted NSW Health to urge people travelling to South East Asia to ensure they are fully vaccinated before heading overseas.
"The most important message is to be immunized", said Dragan Jankovic, a technical officer at the health agency's European vaccine-preventable diseases and immunization program.
Measles is extremely contagious, and can be unsafe, especially for young children.
Gaps in vaccination coverage, complacency about the disease and a resistance by some parents to have their children immunised has been blamed for the concerning rise in infections. Coverage with the first dose of the vaccine also increased slightly to 95%, the highest level since 2013.
Some 82,596 people in 47 of 53 countries contracted measles, the highest number this decade and three times the figure in 2017. Of those, 72 cases were fatal. More children in the Region received the full two-dose series on time, according to their countries' immunization schedules, in 2017 than in any year since World Health Organization started collecting data on the second dose in 2000.
Similar outbreaks have been occurring in Europe: In 2017, there were 25,863 cases of measles; previous year, that surged to more than 82,000.
Dr Zsuzsanna Jakab, WHO regional director for Europe, said: "The picture for 2018 makes it clear that the current pace of progress in raising immunisation rates will be insufficient to stop measles circulation".