Health officials in Indonesia are carrying out a mass immunisation drive after 11 cases of polio were detected in East Java.
The East Java Provincial Health Office reported that as of January 17, 11 children had contracted the rare disease that Indonesia was declared free from a decade ago.
The cases were mainly on the East Java Island of Madura, prompting health officials to declare polio an "extraordinary event" in the province.
Polio is a disease that invades your nervous system and in rare cases can cause incurable paralysis.
Nine of the children were asymptomatic, while two showed clinical symptoms and require intensive treatment, local officials said, according to local media.
In recent years, the World Health Organization (WHO) has only reported a few dozen cases of the disease globally, in Afghanistan, Pakistan and across Africa.
Indonesia and 10 other South-East Asian countries were declared polio-free in 2014 by the WHO.
Meru Sheel, associate professor and epidemiologist at the University of Sydney School of Public Health, said the situation in Indonesia was concerning.
"It means that the virus is now probably actively circulating in many parts of the country," she told the ABC.
Polio is a highly-contagious disease which spreads from person-to-person.
From October 2022 to February 2023, three cases of polio were detected in Aceh province and one case in West Java province.
"So clearly there has been something going on," Professor Sheel said.
Given that there's a lot of movement among the population, the risk of national spread of the disease in Indonesia is quite high, she added.
COVID disrupts vaccination rates
Immunisation disruptions caused by the COVID-19 pandemic are believed to be a factor in the disease's re-emergence.
A report by the University of Sydney and Universitas Indonesia released this week found that education awareness and access to vaccines during the pandemic contributed to significant health services declines in South-East Asia, including Indonesia.
Many children aged from two months to 24 months in Central Java and West Nusa Tenggara provinces were not up-to-date with all vaccines for their age, according to the study.
However, 95.7 per cent of the caregivers said they wanted their child to receive all recommended routine immunisations.
What is polio?
Polio is back in the global conversation again over concerns the disease is spreading in London and New York. Experts say under-vaccination is behind it.
Although nationally vaccination rates may not seem poor, every province has its own health system so there may be pockets of the country that were unvaccinated during COVID, Professor Sheel said.
"Either children have been delayed in getting the vaccine or have missed out because services were closed, or they couldn't get to services," she said.
In response to the current outbreak, Indonesian health authorities have been trying to vaccinate as many children in the area as possible.
Health authorities are aiming to vaccinate 8.4 million children aged 0 -7 years old in Central and East Java, and Yogyakarta.
As of Wednesday, 42.6 per cent of all targeted children, or some 3.6 million children, had received their first dose, according to local media.
Alongside mass vaccinations, authorities need to strengthen community engagement and awareness, and promote vaccine acceptance, Professor Sheel said.
She said conducting environmental surveillance such as sewage sampling and actively finding cases by going house-to-house may be next steps to control the spread.