Authorities in northwestern Pakistan said Monday that a roadside bomb explosion injured at least 10 people, including anti-polio vaccinators and police personnel escorting them.

The bombing in the South Waziristan district near the border with Afghanistan targeted a convoy carrying polio workers and their guards on the opening day of a nationwide immunization campaign.

Area security and hospital officials reported that three health workers and six security personnel were among the victims. No group immediately claimed responsibility for the violence in a region where security forces are fighting militants linked to the outlawed Pakistani Taliban.

Last week, Pakistan reported its 17th wild poliovirus case of the year from Islamabad, saying it paralyzed a child and marked the first infection in 16 years in the national capital.

Pakistani health officials said in the lead-up to Monday’s polio campaign that it is designed to vaccinate more than 33 million children under five in 115 districts nationwide.

Muhammad Anwarul Haq, coordinator of the National Emergency Operations Center for Polio Eradication, stated that the immunization drive would primarily focus on districts where "the virus has been detected and the risk of continued transmission and spread is really high.”

Haq encouraged all parents and caregivers to ensure their children get vaccinated, lamenting that “parents have not always welcomed and opened their doors to the vaccinators when they visit their homes.”

Pakistan and Afghanistan, which reported nine paralytic polio cases so far in 2024, are the only two remaining polio-endemic countries globally. Polio immunization campaigns have long faced multiple challenges in both countries, such as security and vaccine boycotts, dealing setbacks to the goal of eradicating the virus from the world.