MANILA -- The polio virus was detected in some two dozen samples from the environment, indicating that its carriers are continuously "shedding" or spreading the disease in their communities, the health department said Wednesday.

Twenty-six of 142 samples taken from bodies of water and sewage plants tested positive for polio, of which 25 were from the National Capital Region and 1 was from Davao City, the DOH said.

"If viruses continue to spread from person-to-person in areas with low immunization coverage, the polio virus evolves and regains the ability to cause paralysis," Health Secretary Francisco Duque III said.

Duque again urged parents to have their children aged 5 years old and below vaccinated for polio. The DOH on Monday launched the third round of its mass vaccination drive in Metro Manila and the second round in all of Mindanao, which will run until Dec. 7.

The samples were collected from July 1 to Nov. 26 in the NCR, Cordillera Administrative Region, Central Luzon, Calabarzon, Central Visayas, Davao region, Soccsksargen, and the Bangsamoro Autonomous Region in Muslim Mindanao.

Japan's National Institute of Infectious Diseases confirmed the presence of poliovirus types 1 and 2, the DOH said.

In September, the DOH confirmed the re-emergence of polio in the Philippines, nearly 2 decades since the World Health Organization declared the country free from the disease.

Polio is a "highly infectious viral disease, which mainly affects young children," according to the WHO. Severe polio cases may cause paralysis and death. -- With a report from Raphael Bosano, ABS-CBN News