World Health Organisation (WHO) has declared a polio outbreak in Papua New Guinea and called for an "immediate" vaccination campaign. Samples of the highly infectious virus were found in two healthy children during a routine screening in Lae, a coastal city in the country's northeast.Less than half of the country's population are immunised against the potentially deadly disease, which is close to being wiped out, but has recently surfaced in some parts of the world. "We have to do something about it and we have to do it immediately," said Sevil Huseynova, WHO's representative in Papua New Guinea, warning that the disease could spread beyond the country. We have to make maximum effort to get 100% [vaccination] coverage," Dr Huseynova said at a media conference on Thursday. Polio knows no borders.Polio is highly contagious and can be transmitted through droplets from sneezing or coughing, as well as through contact with virus-laden faeces, also known as stool. The virus can easily spread and enter the body through the mouth, and it can also be present in water contaminated with feces from a person infected with the poliovirus. In 1994, India launched the Pulse Polio Immunisation Program to eradicate polio, which at the time accounted for about 60% of global cases. In January 2011, the last reported cases of wild polio in India were in West Bengal and Gujarat. Subsequently, in 2014, the WHO declared India polio-free.