The U.S. Centers for Disease Control and Prevention released a report this week after investigating an outbreak of the delta variant of COVID-19 at an elementary school in California, saying an unvaccinated, infected teacher who took their face mask off to read aloud to the class infected half of their students.
The outbreak happened in Marin County in May 2021 and resulted in a total of 27 cases including the teacher, students, siblings of the students and some parents.
The CDC said the teacher started showing symptoms on May 19 and continued working the next few days despite having a cough, fever and headache. The teacher didn’t have any known COVID-19 exposure and attributed the symptoms to allergies.
Meanwhile, the school’s adherence to masking and distancing in the classroom was said to be high, according to parents who were interviewed as part of the case study. Desks were six feet apart, windows were left open and high-efficiency particulate air filters were in use.
The teacher, however, reportedly went unmasked on occasions when reading aloud in class.
The teacher got tested for COVID-19 on May 21 and on May 23 notified the school the test was positive.
Some students of the teacher began showing symptoms on May 22. Once the teacher tested positive, 22 of the 24 students were also tested. Twelve received a positive result.
The CDC did not elaborate on the students’ age except to say they were too young to be eligible for vaccination. Currently, those 12 and older can get vaccinated with Pfizer’s shot. The CDC said the school serves more than 200 students ages Pre-K through eighth grade.
The CDC noted that the closer the students were sitting to the teacher, the higher their risk was of getting infected.
"Students were seated in five rows; the attack rate in the two rows seated closest to the teacher’s desk was 80% (eight of 10) and was 28% (four of 14) in the three back rows," the report states.
Classroom layout and seating chart for 24 students in index patient’s class, by SARS-CoV-2 testing date, result or status, and symptoms — Marin County, California, May–June 2021. Image: CDC
Also on May 22, students in another classroom who differed in age by three years and were also ineligible for vaccination started showing symptoms.
Fourteen of 18 students in this separate grade received testing, with six testing positive according to the CDC.
One student in this grade was learned to have had a sleepover on May 21 with two classmates. All three of the students experienced symptoms after the sleepover and tested positive.
Additionally, in the following week, four more cases were identified in students in other grades. These four students were siblings of students who got sick from the teacher and exposure was assumed to have happened at home. The CDC did not say if the siblings were old enough to be eligible for vaccination.
Four parents were also infected, for a total of 27 cases.
Among the five infected adults, one parent and the teacher were unvaccinated. The others were fully vaccinated.
The vaccinated adults and one unvaccinated adult were symptomatic with fever, chills, cough, headache and loss of smell, the CDC said.
No other school staff members reported becoming ill. Nobody infected in this outbreak was hospitalized.
The CDC said all sequences that were tested were classified as the delta variant.
All three vaccines currently approved for use in the U.S. are effective at preventing severe infection against the delta variant, though the strain continues to overload hospitals in counties across the country since transmission risk is high among unvaccinated persons. Vaccinated persons have also been found to be able to spread the delta variant if a breakthrough infection occurs.
Nationwide, COVID-19 deaths are running at more than 1,200 a day, the highest level since mid-March. New cases per day are averaging over 156,000, turning the clock back to the end of January.
The CDC says this case study of the outbreak in Marin County "highlights the importance of vaccinating school staff members who are in close indoor contact with children ineligible for vaccination."
As schools are beginning to reopen for the third school year affected by the pandemic, safety measures in the classroom vary by jurisdiction.
In at least 14 states, lawsuits have been filed either for or against masks in schools.
The CDC recommends universal mask-wearing in schools and lists vaccination as the leading strategy to end the pandemic.
It’s unclear how long the ongoing trials or regulatory reviews will take before children younger than 12 will be eligible to get the shot. Results from some tests are expected this fall.
This story was reported from Detroit. The Associated Press contributed.