CDC study: Half of elementary school class caught COVID-19 after exposure to infected teacher

About half of elementary school students in a California classroom tested positive for COVID-19 after being exposed to an infected teacher who had not been vaccinated, highlighting the delta variant’s ability to quickly spread, a federal study released Friday found.

Of the teacher’s 24 students, 22 were tested for the virus that causes COVID-19. Twelve students tested positive between May 23 and May 26, the Centers for Disease Control and Prevention said. All 22 children were too young to receive a vaccine, as the shots have not been approved for youths younger than 12.

In total, 27 cases of COVID-19 were found in the Marin County class, including the teacher. Sequencing of 18 samples identified the highly contagious delta variant of the coronavirus.

The teacher reported experiencing symptoms on May 19 but kept working for two days before getting tested on May 21, according to the CDC report. During that time, the teacher read aloud, unmasked, to the class in violation of school requirements to wear face coverings indoors. 

“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 CDC researchers wrote in their report. “The outbreak’s attack rate highlights the delta variant’s increased transmissibility and potential for rapid spread, especially in unvaccinated populations such as schoolchildren too young for vaccination.”

The “attack rate” of the coronavirus variant was highest for the two rows of kids seated closest to the teacher’s desk, with eight of the 10 students testing positive. For the three back rows, the attack rate was 21%, with three of 14 students contracting the virus. 

Six other students in a different grade who were also too young for vaccination tested positive between May 24 and June 1. Officials confirmed eight more cases among parents and siblings of infected students, three of whom were fully vaccinated.

“In addition to vaccination for eligible persons, strict adherence to nonpharmaceutical prevention strategies, including masking, routine testing, facility ventilation, and staying home when symptomatic, are important to ensure safe in-person learning in schools,” the study authors said.