County officials offered no-appointment vaccinations at three locations until 4 p.m. on Thursday after problems with the MyTurn scheduling system.
People who met the eligibility requirements were able to go for shots at Viejas Arena at San Diego State University, the Lemon Grove Community Center and the East Public Health Center in El Cajon while supplies lasted.
Officials were concerned that some Pfizer vaccine doses would expire if they had gone unused.
At this point, all San Diegans 50 and over are eligible for the vaccine, as are teachers and other essential workers and people with some health conditions. The pool of eligibility is set to expand on April 15, when all San Diegans 15 and over will be eligible for the shot.
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As of Tuesday, 1,047,512 San Diego County residents have had at least one shot of the vaccine; 615,718 of them are fully vaccinated, which is nearly 23% of the county.