LONDON (AP) — Travelers may soon need carry their digital vaccination certificates alongside their suitcases and boarding passes. Keen to avoid losing another summer of holiday revenue to the coronavirus pandemic, the European Union, some Asian governments and the airline industry are scrambling to develop so-called COVID-19 vaccine passports to help kickstart international travel. They would allow travelers to use mobile phone apps to prove they’ve been vaccinated, which could help them avoid onerous quarantine requirements at their destinations. But the multiple efforts underscore the lack of one central international system to electronically verify vaccination status. The projects also face technical challenges in working together, while questions about privacy and vaccine inequality linger.