Cases of a crippling vaccine-derived polio virus could spread in Ebola-ravaged Guinea and in Mali after a Guinean toddler travelled to Mali and became the country’s first polio case in more than four years, the World Health Organisation said yesterday.

The case, caused by a strain of the virus known as type 2 that had come from a vaccine, is the second setback in a week for global efforts to eradicate polio. Two cases were reported in Ukraine last week.

The risk of spread is considered to be high due to low rates of vaccination coverage

Preliminary tests showed the 19-month-old was paralysed on July 20, seven days before being brought to Mali for treatment. The strain is the same as one found in Guinea’s Kankan region in August 2014.

“The risk of spread is considered to be high in both countries due to low rates of vaccination coverage in both Mali and Guinea,” WHO spokesman Cory Couillard said.

Vaccine-derived polio infection are caused when the virus spreads after being excreted by people who have been immunised with live oral polio vaccine. Unvaccinated children and people with low immunity are then at high risk of becoming infected via contaminated water and sewage. Vaccine-derived polio virus (VDVP)outbreaks pose more of a risk in populations where health systems are fragile and immunisation coverage is low.