No additional mutated poliovirus has been detected in sewage samples collected from Kathmandu, the National Public Health Laboratory that regularly carries out environmental surveillance of highly contagious disease said.

Since the presence of type-3 poliovirus in sewage samples was confirmed in May, the central laboratory has stepped up environmental surveillance of the virus, which causes deformities and paralysis in children.

“No additional muted poliovirus has been detected in the sewage samples collected from Kathmandu Valley and other places,” said Dr Ranjan Raj Bhatta, director of the laboratory.

“The National Institute of Health of Thailand, the World Health Organisation’s collaborating centre, which carried out further testing on samples we sent, also confirmed that no additional poliovirus has been detected.”

Nepal has been polio-free since 2010, but was officially declared free of the disease by the World Health Organisation only on March 27, 2014, after maintaining zero polio cases for three consecutive years. After having zero human cases of polio for about 14 years, the infectious disease surfaced in the capital city’s sewage in May.

Type-3 polio virus, which is vaccine-derived, had been detected in sewage samples collected from the confluence of the Tukucha and Bagmati Rivers.

Health authorities launched a mass polio vaccination drive in the three districts of the Kathmandu Valley—Kathmandu, Lalitpur, and Bhaktapur—following the confirmation of the virus in the sewage samples to prevent the outbreak. All children under five years of age will be inoculated with an additional dose of oral polio vaccine in the drive.

Officials at the laboratory said they have been conducting environmental surveillance on a regular basis and sending samples to the UN agency’s reference laboratory in Thailand for cell culture, as the service is available only in a few laboratories across the world.

The national laboratory collects samples from five tributaries in the Kathmandu Valley and from Koshi, Madhesh, and Gandaki provinces to check for the presence of the polio virus.

Doctors say the polio virus mainly affects children and is usually transmitted through droplets or aerosols from the throat and by faecal contamination of hands, utensils, food and water. Those who do not wash their hands properly, and those who consume contaminated food and water or reside in an area where water and sanitation conditions are poor are at high risk of getting infected with the virus.

The Health Ministry said that the vaccine coverage rate for polio is 95 percent throughout the country.

Childhood immunisation is the government’s number one priority, under which 13 types of vaccines are given against a range of diseases, including measles-rubella, pneumonia, tuberculosis, diphtheria, pertussis, tetanus, hepatitis B, rotavirus, Japanese encephalitis and typhoid under the regular immunisation programme, free of cost.

Regular immunisation is one of the most successful programmes in Nepal, with a high coverage rate. The country has shown remarkable progress in reducing the under-five mortality rate and the regular immunisation programme is credited with that.