An unvaccinated Marin County elementary school teacher caused an outbreak of COVID-19 among students and parents at the school in May, according to a new report released by the U.S. Centers for Disease Control and Prevention.
The outbreak at a parochial school led to 27 total cases — five adults, including the teacher, and 22 students or siblings. Of the five infected adults, only two were unvaccinated — the teacher and one parent. All the students involved are too young to be eligible for vaccination. Of the 18 cases that were sequenced, all were found to be the fast-spreading delta variant.
The rash of infections highlights just how contagious the delta variant is, underscoring “the importance of vaccinating school staff members who are in close indoor contact with children ineligible for vaccination as schools reopen,” the CDC report said. Marin County’s high vaccination rate — 72% of eligible people at the time of the outbreak — likely prevented further spread of the coronavirus, the report added.
“This specific outbreak was kind of surprising to us, because at the time we didn’t really know very much about delta,” said Tracy Lam-Hine, an epidemiologist at Marin County Public Health, which led the investigation. He and his team then voluntarily submitted it to the CDC.
The Marin school requires all teachers and students to mask indoors, in line with state guidelines, and the CDC found that adherence to these requirements was high in general. However, the investigation found that the infected teacher had reportedly unmasked while reading aloud to students in class.
While 22 cases were symptomatic — with the most common symptoms being a fever, cough, headache or sore throat — no one was hospitalized. Everyone has since recovered without complications, Lam-Hine said.
The teacher began feeling symptoms on May 19, according to the report released Friday. But the teacher, who had no known exposure to the virus, attributed the nasal congestion and fatigue to allergies and reported to work for two more days before getting a coronavirus test on May 21.
On May 22, students in the class began experiencing symptoms. The teacher’s positive test came in the next day, on May 23. Over the next few days, 22 of the 24 students in the class were tested, and 12 came back positive.
Classrooms at the Marin school all had portable air filters and left their doors and windows open for air flow, and all desks are 6 feet apart. Still, the CDC found that the infection rate of students sitting in the front row — closest to when the teacher was reportedly unmasked — were infected at a much higher rate than students sitting in the back.
However, Lam-Hine said that it’s impossible to know if the unmasking was the cause of the outbreak or if it was a combination of small lapses in the protective measures.
“When there’s things that are very high risk, you have multiple levels of protection, and when one fails, you hope that the other three or four that you have in place hold up,” he said. “In this case, something didn’t line up.”
Also on May 22, students in a different classroom — separated from the infected teacher’s classroom by a large outdoor courtyard and blocked off with yellow tape — also began feeling symptoms. Fourteen of the 18 students in this class were tested, and six tested positive. Investigators still don’t know how the virus spread from the first classroom to this one but assume it was interaction at the school.
Then, starting May 30, more cases started popping up beyond these first two classes — one student each in four different grades tested positive. These four students were siblings of three of the students in the original infected class. Four parents of infected students also tested positive.
To control the outbreak, Marin County Public Health held a mass testing event at the school, testing 231 people — including students, staff and parents — over two days, which helped identify some of the 27 total cases in the outbreak. Still, testing for parents and siblings was voluntary, and some contacts did not want to be tested, according to the report, so the outbreak might have been even larger.
A spokesperson for the public health department said it was contacted right away when the school learned of the first case, and all the correct protocols were followed afterward, with the school helping arrange testing and contact tracing.
“This is not unheard of,” Lam-Hine said of the outbreak, but this experience shows that “with delta and with indoor instruction, we have to be really, really careful.”
“As we have said many times, the best way to protect our children is by vaccinating the adults they come into contact with,” Dr. Abraar Karan, an infectious disease fellow at Stanford University, tweeted about the outbreak.
Lam-Hine said it was important for him and his team to share their findings with the CDC so that other schools can learn from Marin County’s experience.
“This is how public health improves practice,” he said. “We can do this safely. … It’s on schools and individuals. We can all work together on this.
This article was originally published on Website: www.sfchronicle.com
Author is: Danielle Echeverria
”Danielle Echeverria is a San Francisco Chronicle staff writer. Email: danielle.echeverria@sfchronicle.com @DanielleEchev