SYDNEY, July 12 (Xinhua) -- Papua New Guinea's (PNG) Health Minister Puka Temu said on Thursday that the outbreak of poliovirus is now "manageable and not a threat."

"It is a vaccine-related outbreak, not wild polio," he said, adding that people who were vaccinated were free to travel and would not be restricted.

Although the country was officially declared "polio-free" in 2000 and has not had any reported cases since 1996, it was confirmed by the U.S. Centers for Disease Control and Prevention in June, that at least three cases of the infectious disease, known to cause lifetime paralysis in children, had been detected in the nation's second largest city Lae.

In order to contain the spread, the government along with a number of international partners set up a containment zone in the three surrounding provinces of Morobe, Madang and the Eastern Highlands, and are currently implementing a large-scale immunization campaign.

"Our immunization rate over the last 15 years has dropped and that's why this outbreak happened," Temu said.

In order to prevent further outbreaks, the health minister acknowledged that the rate of immunization must improve.

"We have to make sure that we go back to routine immunization, not special immunization," he said.