Pakistan reported two new polio cases in the southern province of Sindh, health officials said Monday, a blow to efforts aimed at eradicating the crippling disease among children. This brings the total to 29 cases across the country since January, despite several immunization drives.

The virus was detected in two young girls in the cities of Badin and Thatta, according to a statement from the Pakistan Polio Eradication Program.

Pakistan and neighboring Afghanistan remain the only two countries where transmission of the wild poliovirus has never been stopped, according to the World Health Organization. Some parents in Pakistan still refuse to vaccinate their children, while others live in hard-to-access areas, experts say.

Meanwhile, health workers sometimes suffer life-threatening attacks when trying to reach households in former militant strongholds in the country’s restive northwest. In February, gunmen killed a police officer assigned to protect a vaccination team in Jamrud, a district in Khyber Pakhtunkhwa bordering Afghanistan. Since the 1990s, more than 200 polio workers and the police assigned to protect them have been killed in attacks.

Authorities said nearly 21 million children under the age of five were vaccinated during a campaign earlier this month. Another nationwide, weeklong door-to-door drive is set to begin Oct. 13, targeting 45 million children.