A health care worker holds an injection syringe of the phase 3 vaccine trial. (Photo by Dogukan Keskinkilic/Anadolu Agency via Getty Images)LOS ANGELES - With a COVID-19 vaccine appearing to likely be on the horizon, health officials are looking ahead to tackle the pandemic’s next chapter: How to prioritize the vaccine’s distribution.Pfizer announced Monday that data shows its potential vaccine is 90% effective in preventing the virus.