The first cases of the child-crippling polio virus in the Philippines for 19 years are a warning for countries such as Ukraine, where low immunity offers fertile ground for viral epidemics, disease experts say.

Ukraine already has a big outbreak of measles – one of the world’s most contagious diseases – with almost 57 000 cases and 18 deaths recorded in the first eight months of this year, according to health ministry figures.

Confidence in vaccines and coverage with childhood immunisations against a range of pathogens have in recent years been dangerously low, World Health Organization (WHO) experts and the UN Children’s fund UNICEF say, leaving large pockets of people vulnerable to viral infections.

“It’s like a time bomb. It’s ticking and it could explode at any time,” said Lotta Sylwander, head of UNICEF Ukraine.

Sylwander’s last post with UNICEF was in the Philippines, where polio has been confirmed as having infected two young children.

Polio is incurable but can be prevented with vaccination and has been successfully eradicated in vast areas of the world in the past few decades. Until last month, it had also been banished from the Philippines, with no cases seen since 2 000.

Its “alarming come-back” in two confirmed cases in places about 1 450 km apart “puts 11 million Filipino children at high risk of disability and even death”,” said Chris Staines of the International Federation of Red Cross and Red Crescent Societies.

Like the measles virus, which has been spreading through both the Philippines and Ukraine for at least a year, polio can pose a risk unless at least 95% of the population is vaccinated.

Polio immunisation coverage in the Philippines is at 70%. In Ukraine in 2017, only 51.9% of babies under a year old were immunised against polio, UNICEF says. Last year that rose to 69.2%.

Oliver Rosenbauer, the WHO’s spokesperson for the Polio Eradication Initiative, described polio as “a highly infectious and epidemic-prone disease” and said a range of factors can contribute to low rates of immunisation: Vaccine hesitancy, community resistance, lack of infrastructure, lack of supply, patchy health services, war and conflict.

“Polio virus is very good at finding unvaccinated children and for sure there are vaccine coverage gaps,” he said.

Heidi Larson, director of the Vaccine Confidence Project which tracks immunisation coverage and attitudes to vaccines around the world, noted the “worrying” pattern of polio’s return to the Philippines amid a measles outbreak, and said Ukraine’s measles epidemic is a “canary in the mine” warning.

“The challenge now in Ukraine is whether in the face of all this measles, have they kept up their guard against polio,” she told Reuters.