Eritrea launched a campaign on Monday to inoculate 500,000 children against polio, using camels to deliver vaccines to more remote corners of the country.

Although polio has not been recorded in Eritrea since 1997, cases have recently appeared in neighboring Ethiopia and Sudan.

Solar power is being used to keep the vaccines cold as health workers distribute them to areas where electricity is scarce or non-existent. The sweltering heat in Eritrea would kill the vaccines if they were not kept cool.

“We have had practically no rain here for three years,” Dr Miheretu Mesfin said at his clinic in Adihawesha, a stony village 9 miles outside the capital Asmara.

A solar-powered fridge at the clinic cools the vaccines, and supplies the ice for Mesfin’s four teams so they can deliver them to nearby villages.

“The fridge is good for routine vaccines, but a bit small for such a big campaign,” Mesfin said as mothers began queuing outside with their children.

In the rural areas where roughly 80 percent of Eritrea’s population lives, health workers will fan out on foot or by camel and public transport to deliver the vaccine, he said.

Some 23 countries are immunizing 100 million children in Africa, to contain the recent re-emergence of the disease on the continent, UNICEF said.