The Vanuatu Ministry of Health has reported two cases of diphtheria and is working with the World Health Organisation (WHO) and the UN children's agency (UNICEF) to improve detection and treatment.
The ministry said there had been an increase in vaccine preventable diseases this year.
Recent testing done in New Caledonia revealed two children, aged 11 and 13, had diphtheria, which can be fatal if not treated, it said.
Diphtheria is easily spread from person to person through coughing and sneezing and close physical contact.
Once identified the disease can be treated with antibiotics.