An unvaccinated teacher infected over a dozen students and some of their parents, according to this study.
It was May 2021, the school year was ending and Marin County was on the cusp of reaching a milestone with the highest vaccination rate in the country.
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A month before that milestone was reached, a COVID-19 outbreak at a school happened.
"We had someone let their guard down," said Mary Jane Burke, Marin County Superintendent of Schools.
Friday, the CDC published a study providing insight into a COVID-19 outbreak at an un-named elementary school in Marin County. It shows 22 students were infected with COVID by an unvaccinated teacher.
"An unvaccinated person and someone who took their mask off to read to children occasionally. If this wasn't Delta we wouldn't have seen this outbreak event," said Dr. Lisa Santora, Marin County Deputy Public Health Officer.
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The lead author of this paper is Marin County public health epidemiologist Tracy Lam Hine.
"Students that were sitting in front of the classroom closer to the teacher were at higher risk, and we noticed that the infection in the students started to appear quite quickly right afterwards," said Tracy Lam-Hine.
Lam-Hine says contact tracing led them to the teacher and confirmed that even though this group of students were too young to get vaccinated they were not severely sick.
"The most common report of symptoms were fever or headache and a cough," said Lam-Hine.
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Marin County Deputy Public Health Officer says this outbreak provided some of the first signs that Delta was different and breakthrough cases were happening.
"Some of the parents who got sick were asymptomatic, they were vaccinated, asymptomatic and just got tested and found out they positive," said Dr. Lisa Santora and added,
According to Marin County's school district, out of 6,000 school staff members, close to 200 are unvaccinated.
To work at a school they have to wear a mask indoors and get tested at least once a week, but vaccines are not mandated.
Luz Pena: "Do you believe teachers should be mandated to get vaccinated?"
Mary Jane Burke: "I do, I do."
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Marin County Superintendent of Schools says this outbreak is making them look into the possibility of mandating vaccines.
"It very likely could be that you won't be able to continue working with children without being fully vaccinated," said Mary Jane Burke.
The Deputy Public Health Officer says mandating teachers to get vaccinated is not part of their plan.
"When everyone is wearing their masks indoors and outdoors, when the staff are fully vaccinated. When people are staying at home when they are sick. We don't see school based transmission," said Dr. Santora