As per a CDC report, a major outbreak originated in the US when an unvaccinated teacher infected a number of children creating a chain of multiplied infected cases. This incidence highlighted the Delta variant's rapid transmissibility and the importance to have vaccinated staff members along with strict COVID prevention strategies in places where educational institutions have reopened.

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On August 27th this year, the Mortality and Morbidity Report published by the Centers for Disease Control and Prevention (CDC) vividly described how an unmasked, unvaccinated teacher infected a dozen children in a US school with SARS-CoV-2 B.1.617.2 (Delta) variant - a strain that is highly transmissible.

The CDC report offers useful insights to those starting to open their schools. Teachers and others associated with teaching unvaccinated students may realise what is in store for them if they are careless and casual in their approach. The incident highlights the need for absolute, unquestioned compliance with COVID appropriate norms by everyone.

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The incidents in the school

During the period between May 23rd and June 12th, 2021, laboratory-confirmed 26 COVID-19 cases occurred among elementary school students and their contacts. Exposure to an unvaccinated infected teacher caused the spread of the disease. The investigation by researchers from the County of Marin Department of Health and Human Services, San Rafael, California, University of California and Napa-Solano-Yolo-Marin-Mendocino County Public Health Laboratory, Fairfield, California showed that the attack rate in one affected classroom was 50% and the risk correlated with seating proximity to the teacher.

It all started on May 25th, 2021, when an elementary school notified the Marin County Department of Public Health (MCPH) that on May 23rd, an unvaccinated teacher had reported receiving a positive test result for SARS-CoV-2. The teacher became symptomatic on May 19th but continued to work for 2 days before receiving a test on May 21st.

The school required everyone while indoors to wear a mask. The teacher read aloud unmasked to the class. Starting after two days, the school noted additional cases of the disease among other staff members, students, parents, and siblings connected to the school.

On May 26th, MCPH started diligent case investigation and contact tracing that included whole-genome sequencing (WGS) of available specimens to characterise the outbreak. The agency identified 27 cases including that of the teacher. From May 23rd to 26th, among 24 students, 22 were ineligible for vaccination because of age. However, when tested for SARS-CoV-2, 12 received positive test results.

The attack rate in the two rows seated closest to the teacher’s desk was 80% (8 of 10) and 28% (4 of 14) in the three back rows. From May 24th to June 1st, out of 18 students, 6 were in a separate grade at the school, and also too young for vaccination, received positive SARS-CoV-2 test results. MCPH identified 8 additional cases - all in parents and siblings of students in these two grades.

Among these additional cases, 3 were in persons fully vaccinated in accordance with CDC recommendations. Among the 27 total cases, 22 (81%) persons reported symptoms (the most frequently reported symptoms were fever - 41%, cough - 33%, headache - 26%, and sore throat - 26%).

Whole Genome Sequencing (WGS) of all 18 available specimens identified the B.1.617.2 (Delta) variant. The researchers noted that vaccines are effective against the Delta variant, but the risk of transmission remains elevated among unvaccinated persons in schools without strict adherence to prevention strategies. They asserted that besides vaccination for eligible persons, strict adherence to non-pharmaceutical prevention strategies, including masking, routine testing, facility ventilation, and staying home when symptomatic, is important to ensure safe in-person learning in schools.

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Investigation and findings

The school serves 205 students in pre-kindergarten through the eighth grade and has 24 members of staff. Each grade includes 20 to 25 students in single classrooms. Other than 2 teachers, one of whom was the index patient, all school staff members received vaccinations. The index patient was symptomatic on May 19th with nasal congestion and fatigue. This teacher attended social events during May 13th and16th but did not report any known COVID-19 exposures and attributed the symptoms to allergies.

The teacher continued working from May 17th to 21st, subsequently experiencing more symptoms like cough, subjective fever, and headache. Interviews with parents of infected students suggested that students’ adherence to masking and distancing guidelines in line with CDC recommendations was high in class.

The teacher reportedly did not wear a mask on occasions when reading aloud in class. On May 23rd, the teacher notified the school that she received a positive result for a SARS-CoV-2 test performed on May 21 and self-isolated until May 30. The teacher did not receive a second COVID-19 test, but she reported fully recovering during isolation.

The index patient’s students began experiencing symptoms on May 22nd. During May 23rd and 26th, among 24 students in this grade, 22 were tested. 12 students (55%) of the 22 received a positive test result, including 8 who experienced symptoms onset during May 22nd and 26th. Throughout this period, all desks were separated by 6 ft. Students were seated in five rows. The attack rate in the two rows seated closest to the teacher’s desk was 80% (8 of 10) and was 28% (4 of 14) in the three back rows.

The researchers reported that on May 22nd, students in another classroom, who differed in age by 3 years from the students in the class with the index case, and who were also ineligible for vaccination began to experience symptoms.

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Conditions in the classroom

A large outdoor courtyard with lunch tables that the school authorities blocked off from use with yellow tape separated the two classrooms. All classrooms had portable high-efficiency particulate air filters and doors and windows remained open.

14 of 18 students in this separate grade received testing, where 6 tested positive. One student in this grade hosted a sleepover on May 21st with two classmates from the same grade. All 3 of these students experienced symptoms after the sleepover and received positive SARS-CoV-2 test results. Among infected students in this class, test dates ranged from May 24th to June 1st. Symptoms onset occurred from May 22nd to 31st.

Besides the documented infections in the two initial grades, researchers identified 1 student each from four other grades. 3 patients were symptomatic. The dates for testing were May 30th and June 2nd. These 4 students were siblings of 3 students with cases in the index patient’s class. Researchers assumed that their exposure must have occurred in their respective homes.

Besides, the teacher and 22 infected students, 4 parents of students with cases were also infected. For 27 cases, 23 were confirmed by RT-PCR and 4 by antigen testing. Among the 5 infected adults, 1 parent and the teacher were unvaccinated. The others received full vaccination. The vaccinated adults and one unvaccinated adult were symptomatic with fever, chills, cough, headache, and loss of smell. No other school staff members reported becoming ill and no persons were hospitalised.

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Follow up action

During the tests done on May 26th and June 2nd, at the school as a part of outbreak control, MPCH tested 231 persons, including 194 of 205 students, 21 of 24 staff members and teachers, and 16 parents and siblings of students.

By analysing the results of Whole Genome Sequencing, the researchers found that all sequences generated were classified as the Delta variant. They could also suggest that infections occurring in the two grades likely were part of the same outbreak.

Following the outbreak, officials isolated the infected persons for 10 days after onset of symptoms (or positive test date for asymptomatic cases). All students with known exposure to an infected person remained in quarantine at home for 10 days, following their last known contact.

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The lessons from the outbreak

According to the researchers, the outbreak that originated with an unvaccinated teacher highlighted the importance of vaccinating school staff members who are in close indoor contact with children ineligible for vaccination as schools reopen.

The researchers added,

"The outbreak’s attack rate highlights the Delta variant’s increased transmissibility and potential for rapid spread, especially in unvaccinated populations such as school children too young for vaccination."

They observed that transmission to community contacts appeared lower than that of some previously reported Delta variant outbreaks and high levels of community vaccination might have prevented further transmission. During this outbreak, approximately 72% of eligible persons in the city where the school is located received full vaccination.

The team cautioned:

"These findings support evidence that the current COVID-19 vaccines with Food and Drug Administration approval or Emergency Use Authorisation are effective against the Delta variant. However, transmission risk remains elevated among unvaccinated persons in schools. In addition to vaccination of eligible persons, implementation of and strict adherence to multipronged non-pharmaceutical prevention strategies including proper masking, routine testing, ventilation, and staying home while symptomatic are important to ensure safe school instruction."

The team conceded that its study is subject to some limitations. School children are vulnerable. They are ineligible for vaccination because of age. These reasons might have caused rapid transmission and vaccine breakthrough infections during the outbreaks.

The application of non-pharmaceutical prevention strategies, including routine testing, ventilation, and staying home while symptomatic, is also important for protecting the health of school children ineligible for vaccination because of their age.

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Let me conclude by quoting what Bruce Y Lee, Senior Contributor to Forbes wrote in his news story on the topic: "Again, all of this occurred simply because one teacher did not get vaccinated and did not wear a face mask while teaching in the school. It’s a reminder that while air filtration and good ventilation can be helpful, they may not overcome the virus geyser that may come out of an unmasked nose and mouth unless you turn the school into a jet propulsion laboratory wind tunnel".

Disclaimer- The views and opinions expressed in this article are those of the author's and do not necessarily reflect the official policy or position of M3 India.

Dr K S Parthasarathy is a former Secretary of the Atomic Energy Regulatory Board and a former Raja Ramanna Fellow, Department of Atomic Energy. A Ph. D. from the University of Leeds, UK, he is a medical physicist with specialisation in radiation safety and regulatory matters. He was a Research Associate at the University of Virginia Medical Centre, Charlottesville, USA. He served the International Atomic Energy Agency as an expert and member in its Technical and Advisory Committees.