A study conducted by the U.S. Centers for Disease Control and Prevention shed light on a COVID-19 outbreak in a Bay Area school amid the threat of the more infectious delta variant.

On Friday, the center released a report stressing the importance of vaccination and “strict adherence to multiple nonpharmaceutical prevention strategies, including masking” to ensure that both learners and educators are safe with the return of in-person education.

The outbreak dates back to May where a Marin county pre-K-8 school educator, who was not identified, tested positive after manifesting symptoms that included fatigue and a stuffy nose.

At that time, a report from SFist said that a couple of delta variant outbreaks happened in Novato schools but no Novato public schools align with CDC’ information.

Despite the presence of symptoms, the teacher still reported working for a couple of days, insisting that she suffers from just allergies. This placed the class at risk of infection.

The outbreak has recorded a total of 12 students infected and 27 individuals confirmed positive for the delta variant.

It was found out that most of the students infected by the virus are sitting at the front seat in the virus-infected teacher’s class.

Masks were worn inside the classroom, which is equipped with an air filter as physical distancing was practiced. But it was suspected that the learners and the teacher took their masks off during a reading activity.

According to the CDC, fifteen more cases including six learners from another classroom, four siblings of the learners, three parents of the students from another room, and another teacher were identified.

Only a teacher and one of the parents were found to have been vaccinated.

“The lesson for us is that we have all these different vaccination and nonpharmaceutical strategies to prevent outbreaks in schools and we layer them all,” Tracy Lam-Hine, Marin County epidemiologist, told SFGATE.

“We want different backups in case something fails; and it may have been the unmasking that caused the failure, but it’s hard to say for sure.”