An unvaccinated French boy is suspected of reintroducing measles to Costa Rica after the Central American country had been free of the disease for five years.

The five-year-old boy, who was on holiday with his parents, had never had a measles jab and the arrival of the highly contagious disease has sparked concern about the anti-vaccine movement.

It is not clear why the child was not vaccinated.

The World Health Organisation (WHO) warned last month that “vaccine hesitancy” was among the 10 most serious threats to human health.

“Some countries that were close to eliminating measles have seen a resurgence,” the WHO warned.

Agnès Buzyn, the French health minister, last year made vaccinations against measles and 11 other diseases compulsory for children.

Ms Buzyn has made extending vaccination coverage one of her top priorities.