Mass vaccination of 15,000 Twin Cities educators will begin at the Xcel Energy Center in St. Paul Thursday, but not all 15,000 originally prioritized for the shots will get them.

Sharing of a sign-up link intended for specific teachers created the glitch, resulting in appointments being quickly filled Tuesday night by some educators who weren't prioritized, and some schools getting shut out. Lionsgate Academy was slotted for 87 shots, for example, but only one of its teachers got an appointment.

"I'm very pleased with who it went to — it's a very, very well-qualified candidate for vaccine," said Gael Braddock, a human resources official for the charter school, "but it would be great if we could get the rest of them. We're a little confused."

The Minnesota Department of Education changed its approach to vaccine registration from last week, when only 6,000 doses were available statewide for educators, to this week, when double the doses were made available just in the metro area.

In the first week, quantities were small enough for districts to survey individual teachers and register them. This week required a broader approach.

St. Paul Public Schools went from 88 designated doses in week one to a second-week target of 2,049 doses, which district spokesman Kevin Burns said were prioritized for teachers returning to in-person classrooms Monday.

However, two high school principals shared the registration link with others, who then forwarded it to still others — resulting in people signing up who weren't invited, said Nick Faber of the St. Paul Federation of Educators Local 28.

"We know mistakes are going to happen," he said. "We would have a lot of grace about this if these folks weren't going in front of kids Feb. 1."

The Moderna COVID-19 vaccine is given in two doses four weeks apart. It is considered 95% protective after both doses have been administered.

St. Paul Public Schools issued a statement regretting that staff shared the link, despite warnings not to do so.

"Moving forward, we will continue partnering with the state, and work to improve the parts of the process we control," said Jacqueline E. Turner, the district's chief operations officer, in an e-mail to staff.

Many providers have extracted extra doses out of the 10-dose vials, so it's possible the five-day vaccination event could stretch to more teachers, said Amanda Frie, site leader for the event.

Convention space at Xcel was organized with 36 vaccine stations capable of providing 375 shots per hour, she added.

Teachers will check in first to make sure they are on the sign-up registry. Because of the broad distribution of the link, state education officials are going through the list to make sure everyone who signed up is at least an educator or child-care provider.

Districts only had rough targets for vaccine slots this week, not guaranteed numbers, said MDE spokesperson Ashleigh Norris. However, she said state leaders will take lessons from this "pilot site" to improve future events and to target registration to priority groups.

"The good news is we're going to be able to get in the metro 15,000 educators and child care providers vaccinated this week," Norris said.

Sign-up required people to list their employers as well as a password, but the password was shared as well or was found in the source coding of the registration page.