Over 7,000 children between six and eight years of age are out of school in the Kathmandu district and could miss the inactivated polio vaccine (IPV) in the ongoing immunisation drive, health authorities estimate.

Officials said they only have an estimation of the number of children in that age bracket but do not know their whereabouts.

“Children in the floating population, of parents working in construction sectors and factories or of those residing in slum settlements, who do not go to school, are the high-risk groups but they could be deprived of the vaccination programme,” said Dr Arjun Sapkota, chief of the Health Office, Kathmandu.

“We will run a vaccination programme in health facilities on the last day of the campaign, but we are unsure if all the children missing the vaccine will get inoculated.”

The Ministry of Health and Population launched a nationwide immunisation drive on Sunday, targeting over 1.46 million children born between April 2016 and October 2018 who have missed the inactivated polio vaccine (IPV) due to a global shortage. Those children were administered only Type-1 and Type-3 polio oral vaccines and had missed the Type-2 polio vaccine.

Officials at the Immunisation Section of the Family Welfare Division under the Department of Health Services estimated that thousands of children throughout the country neither go to school nor participate in health care programmes.

“Providing health care services, including routine vaccines, to those populations is the most challenging task,” said Dr Abhiyan Gautam, the section chief. “Chances of those groups missing the services, including the routine vaccines, are always there. We will send health workers to the at-risk areas to find such children.”

Healthworkers found over 74,000 children out of school nationwide during the measles-rubella campaign launched in February.

“We are aware of the children who are out of school,” said Gautam. “Floating population, scattered slums, working-class people, lack of awareness and poor access to health workers are major challenges to health workers. We will send health workers to the areas designated as risk zones.”

Nepal has been polio-free since 2010, but the World Health Organisation officially gave the status on March 27, 2014, after maintaining zero polio cases for three consecutive years.

After introducing the IPV vaccine in September 2014, the country switched to the bivalent oral poliovirus vaccine (bOPV0) from the trivalent oral poliovirus vaccine (tOPV).

The trivalent oral poliovirus vaccine contains all three types of poliovirus: Type-1, Type-2, and Type-3. The current oral poliovirus vaccine is made up of live, attenuated poliovirus.

The trivalent poliovirus vaccine was effective against all three types of poliovirus.

However, the Type-2 component of this vaccine can lead to the circulation of vaccine-derived viruses. Its use was linked to a vaccine associated with paralytic polio, a condition in which children develop paralysis.

Nepal became the first country in South Asia to incorporate the IPV vaccine in its routine immunisation programme in line with the UN health body’s endgame strategic plan to eliminate the risk of vaccine-derived poliovirus and phase out all oral polio vaccines in the routine immunisation programme.

IPV consists of inactivated poliovirus strains of all three poliovirus types.

Health officials say that children should continuously receive the bivalent poliovirus vaccine, even if they are administered the IPV vaccine, as the bivalent poliovirus vaccine is also necessary for intestinal immunity, while IPV provides mucosal immunity.

The government's number one priority is childhood immunisation, under which 13 types of vaccines are given free of charge 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.

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

However, the Nepal Demographic and Health Survey-2022, carried out by the Ministry of Health and Population, showed that at least four percent of the children aged between 12 and 23 months received no vaccine at all.

This figure was one percent in 2016. The Ministry of Health and Population said that the nationwide vaccine coverage rate for polio is 95 percent.