CDC report links unvaccinated Marin County teacher to May COVID-19 school outbreak

An unvaccinated and sometimes unmasked teacher at a Marin County private elementary school set off a COVID-19 outbreak in May that spread to more than two dozen students, siblings and parents, a new report from Marin Health and Human Services has found.

The report released Friday and published by the U.S. Centers for Disease Control and Prevention said the outbreak shows how easily the virus’s highly contagious delta variant can spread at school — including among elementary students too young for shots — and the importance of masks and other measures as kids return to the classroom.

“This outbreak of COVID-19 that originated with an unvaccinated teacher highlights the importance of vaccinating school staff members who are in close indoor contact with children ineligible for vaccination as schools reopen,” the authors wrote. “Proper masking, routine testing, ventilation and staying home while symptomatic are (all) important to ensure safe school instruction.”

The report didn’t name the school, but it appears to be the parochial school, Our Lady of Loretto in Novato, linked in May to what Marin County health officials say was their largest

school outbreak. The principal did not respond, but the Archdiocese of San Francisco said in a statement that the incident referred to in earlier news accounts and Friday’s CDC report “was an isolated circumstance and has been addressed internally.”

A total of 27 people were infected in the outbreak, including the unnamed teacher, students in two different classrooms and their family members, the report said. All the infected students were under age 12 and too young to be vaccinated. Only two of the school’s teachers were unvaccinated, including the infected teacher. No other staff tested positive. More than half the infected family members were unvaccinated. But three of the parents who got sick were vaccinated. They all came down with fever, chills, cough, headache and loss of smell — well before it became clear how vulnerable the inoculated were to delta.

The infected teacher had attended social events May 13-16 and did not know of any COVID-19 exposure but began feeling fatigue and nasal congestion May 19, the report said. Believing the symptoms were from allergies, the teacher continued working May 17-21 as coughing, headaches and fever set in.

The teacher’s classroom had an open door and windows plus an air purifier, and the state at the time required staff and students at schools to wear masks indoors and out. The report found that students adhered to the mask requirement, but that the teacher was reportedly unmasked on occasions when reading aloud in class.

The teacher got tested May 21 and was confirmed positive for COVID-19 two days later, the report said. It found that the teacher had infected half of the 24 students in the classroom, and that eight of those 12 were seated in the two rows closest to the teacher’s desk.

In addition, six of 18 students in a separate grade at the school, all too young for vaccination, also tested positive for COVID-19, as did eight family members of the students in those two grades, the report said. Four of those were siblings of the students in the infected teacher’s class who attended the school in other grades. The other four were parents, three of whom were fully vaccinated. Genetic sequencing identified the virus involved as the highly transmissible and now dominant delta variant, the report said.

Tracy Lam-Hine, a Marin Health and Human Services epidemiologist and lead author on the study, said Friday that it was unclear how the outbreak spread from the infected teacher’s classroom to kids in another class.

“It’s a mystery,” Lam-Hine said. “We spent tons of time trying to find that link.”

But it appeared some of the spread among students in the second class was linked to a sleepover.

The report said that although three of the infected students’ vaccinated parents also caught the virus, any spread beyond the school likely was limited by the community’s high vaccination rates, with about 72% of those eligible being fully vaccinated at the time.

Fortunately, all of those infected recovered, and none became severely ill, Lam-Hine said. But Marin health officials felt that their findings about the outbreak were important to share nationally as kids return to campuses this month for the new school year. For many in California, it’s their first full-time, in-person instruction since March 2020, and it comes amid community outbreaks of the delta variant.

Dr. Lisa Santora, Marin County’s deputy health officer, said the “breakthrough infections” of vaccinated parents at a time when the delta variant was not yet dominant and spreading rapidly across the country “was a canary in coal mine scenario for us” signaling the continued need for face masks and other protections.

“This showed our vulnerability, even as a highly vaccinated community, to the delta variant,” Santora said.

Though reported infections among school staff and students have multiplied around the state this month as kids returned to schools, there has been little sign of spread on campuses. Santora said they have had a total of 50 positive staff and student cases since nearly 40,000 public and private school kids started school in Marin County, none involving spread on campuses among students and only one possible spread from one staff member to another.

With many parents protesting the state’s current mandate for masks indoors at schools — several schools also require them outdoors — and others fearful of sending their kids back at all, Bay Area health officers this week joined in a statement that in-person learning must continue and can be done safely.

“We have tools that work,” Santora said.

Santa Clara County Health Officer Dr. Sara Cody said Thursday that although the county hasn’t documented outbreaks with inschool spread so far, “it will happen.”

“It’s a matter of time,” Cody said. “And the good thing to know is that schools have plans in place. They’ve been working very closely on their plans to catch it early and prevent further spread.”