The World Health Organization (WHO) is preparing a mass polio immunisation campaign for 500,000 children in Gaza, after the virus that causes the highly contagious disease was detected in wastewater samples around displacement camps last month. The shots come from global stockpiles, and while WHO Director-General Dr Tedros Adhanom Ghebreyesus has already signed off on their use, they’re sitting in storage in Indonesia because the WHO is facing major barriers to launch the effort, officials said during a press briefing on Wednesday. That includes transportation issues, uncertainty around cold-c…