A six-year-old boy who had not been vaccinated is Spain’s first case of diphtheria in 28 years. The young boy, from the Catalan city of Olot, is reportedly very ill and is being treated with antitoxin. The parents, who had chosen not to vaccinate their child, are “devastated” and have now had their younger daughter immunized as a result.

Diphtheria is a bacterial infection that spreads through coughing or sneezing, according to the World Health Organization. Once infected, sufferers can experience a sore throat, fever and swollen glands in the neck. Diphtheria can lead to serious complications even with treatment, with 10% of cases resulting in death. Spain’s Health Ministry had to scramble to find the drug to treat the child as there had not been a case of diphtheria in Spain for almost 28 years due to the country’s high vaccination coverage (over 95%). The antitoxin was eventually delivered from Moscow to Barcelona by the Russian ambassador.

“The family is devastated and admit that they feel tricked, because they were not properly informed,” Catalan public health chief Antoni Mateu told El País. “They have a deep sense of guilt, which we are trying to rid them of.”

The child remains in critical condition in Vall d’Hebron hospital’s intensive care unit, but is responding to treatment. Health officials have launched an investigation to find the original carrier, which they admit could be difficult if the carrier isn’t showing any symptoms. All those in contact with the child are under surveillance, and his classmates have been checked to see if they’ve been vaccinated. As a cautionary procedure, they have also given the children preventive medicine.

“Vaccination is the best way to prevent diphtheria,” the WHO said in their report. They warn of the risks of parents hesitating or refusing to vaccinate their child, as gaps in coverage can accumulate and result in an outbreak. The WHO is working closely with the Spanish Ministry of Health and calls for increased vigilance to improve monitoring systems, raise awareness of the importance of vaccination and strengthen immunization programs.