How the Delta variant infiltrated an elementary school class


An unvaccinated elementary school teacher infected with the highly contagious Delta variant spread the virus to half of the students in a classroom, causing an epidemic that ultimately infected 26 people, according to a new report from the Centers for Disease Control and Prevention .

The unusually detailed study, which comes as school districts across the country reopen, looks certain to intensify debate over school vaccination mandates. A handful of school districts, including New York City, have already announced vaccine requirements for teachers and staff.

Others may follow suit now that the Food and Drug Administration has granted full approval for the Pfizer-BioNTech vaccine.

“The most important thing we can do to protect school children, especially those who are too young to be vaccinated, is to make sure the adults in their lives, including teachers and school staff, are vaccinated.” , said Jennifer Nuzzo, epidemiologist at Johns Hopkins University. , who was not involved in the report.

The study was one of three new CDC reports that focused on schools or children. In another study, researchers found more evidence that schools can be low-risk environments when they combine multiple precautionary measures. But this research was carried out before the Delta variant started to spread.

A third report looked at adolescent vaccination rates. Half of the 12 to 17-year-olds have received at least one dose of a coronavirus vaccine, the White House said on Friday. But the new study found that vaccination rates for this age group remained very uneven across the country.

Together, the studies highlight both how much scientists have learned about how to protect children in schools – and how much remains uncertain now that the Delta variant has arrived.

The classroom outbreak occurred in Marin County, Calif., In May. Neither the school, nor the staff members and students involved have been identified.

The teacher first showed symptoms on May 19, but worked for two days before getting tested. Meanwhile, the teacher read aloud, unmasked, to a class of 24 students, despite rules requiring teachers and students to wear masks indoors.

All of the students were too young for the vaccination, which is only allowed for people 12 years of age and older.

On May 23, the teacher said he tested positive for coronavirus infection. Over the next few days, 12 of the students also tested positive.

“I thought I respected his contagiousness,” said Dr Lisa Santora, assistant health worker at Marin Health and Human Services and author of the report, of the Delta variant. But her efficiency in overtaking the class “surprised and humiliated her”.

In the classroom, the infection rates roughly matched the seating plan. Everyone in the first row tested positive, decreasing to 80% in the first two rows.

In the last three rows, only 28% of students tested positive. “If the teacher doesn’t have a mask, move to the back of the classroom,” Edward Traver, an infectious disease researcher at the University of Maryland Medical Center, said in a Twitter message.

Six students from another grade at school have also tested positive for the virus. The cases have spread from the school to the community: At least eight parents and siblings of the infected students, three of whom were fully vaccinated, were also infected.

State health researchers sequenced virus samples from many positive cases and found all of them had been infected with the Delta variant. Samples of at least 10 students from two grades were genetically indistinguishable. The results suggest that the cases in both classes were from the same outbreak.

The outbreak was likely fueled both by Delta’s high level of infectivity and the teacher’s failure to follow recommended safety precautions, the researchers said.

“We need to make sure that schools and individuals work together to keep us safe,” said Tracy Lam-Hine, epidemiologist at Marin County Health and Human Services and author of the new report. “It can’t be just one or the other.”

In other parts of the country, the tribute to the community could have been even higher. Marin County has the highest vaccination rate in California. The report noted that 72 percent of eligible people in the surrounding community were fully vaccinated and suggested that high rates may have prevented further transmission.

In another new study, researchers focused on case rates in Los Angeles County, where some students and teachers attended school in person last year, while others did so in distance.

Schools open for in-person learning had to take a variety of precautions, including symptom screening, masking, physical distancing and contact tracing. During most of the period between September and March – and particularly during the winter wave – case rates were lower in schools, for both teachers and students, than they were in the whole county.

The results are consistent with previous studies which found that when schools combine multiple protective measures, case rates are often lower in schools than in the surrounding community.

“School is a safer place in many ways for young people because it is so structured and supervised,” said Dr Santora, who has a 9-year-old and an 11-year-old returning to school. in-person school this fall. .

But studies of mitigation measures in schools, including the Los Angeles report, were conducted before the Delta variant began to spread. The variant is about twice as transmissible as the original version of the virus and now accounts for nearly all infections in the United States.

It is not yet known whether the same types of precautions will control the variant in schools this year, and many schools have opened without the safety measures recommended by public health experts.

Siobhan Flynn, who teaches first year at a Washington-area charter public school, is worried about the resumption of classes on Monday. The school Ms. Flynn works at uses a layered protection approach that includes a mask warrant, social distancing offices, and random testing for students.

“The kids need to be in school, but I just wish more money and planning had gone into making schools safe,” Ms. Flynn said. “A lot of people would feel a lot safer if all staff were vaccinated. “

Vaccination rates have increased in recent weeks as Delta continues to generate a nationwide spate of cases, hospitalizations and deaths. But parents are afraid to send young children back to school when they cannot yet be vaccinated.

The FDA first cleared the vaccines for 12 to 15 year olds in May, and as of July 31, more than a third of them had received at least one injection, according to a third CDC report. More than half of 16-17 year olds, who were eligible for the vaccine months earlier, had received at least one dose.

But vaccination rates vary widely across the country. In Mississippi, only 11% of teens have been fully immunized, compared to 60% in Vermont, the researchers found.

Dr Westyn Branch-Elliman, an infectious disease researcher at Harvard Medical School, said in an email that she hoped to see schools “get more involved in promoting immunization for all who are eligible in the school community through things like setting up immunization clinics. in schools to improve access and reduce barriers.

Clinical trials of vaccines in young children are underway. Pfizer said the results should be available in September.


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