Israeli air raids in the Gaza Strip killed more than a dozen people overnight into Saturday, hospital and local authorities said, as health workers were wrapping up the second phase of an urgent polio vaccination campaign designed to prevent a large-scale outbreak in the territory.

The vaccination drive was launched after health officials confirmed the first polio case in the Palestinian enclave in 25 years, in a 10-month-old boy whose leg is now paralyzed. The nine-day campaign by the U.N. health agency and partners began last Sunday in central Gaza and aims to vaccinate 640,000 children under the age of 10, an ambitious effort during a devastating war that has destroyed Gaza’s health care system and much of its infrastructure.

The second phase of vaccinations in the south was in its final day Saturday, the Gaza Health Ministry said, before moving to the north and concluding on Monday. The ministry designated dozens of vaccination points across the southern cities of Khan Younis and Rafah.

Israel, meanwhile, kept up its military offensive. In central Gaza’s urban refugee camp of Nuseirat, Al-Awda Hospital said it received the bodies of nine people killed in two separate air raids. One hit a residential building early Saturday, killing four people and wounding at least 10, the hospital said, while five people were killed in a strike on a house in western Nuseirat.