Covid: Delta variant, from infected teacher to kids

 The CDC just reported an outbreak of Delta variant in an elementary school classroom in Marin County, California from an infected teacher, with a 50% attack rate on kids (see https://www.cdc.gov/mmwr/volumes/70/wr/pdfs/mm7035e2-H.pdf  ). 

 

Details: 

-- the Marin County elementary school has 205 students in pre-kindergarten through 8th grade, and 24 staff members 

    -- each classroom has 20-25 students 

-- on May 23 there was an outbreak of Covid from an unvaccinated teacher to many in the class (confirmed by PCR or antigen testing) 

-- the teacher had symptoms on May 19 but continued to work until May 21 (this teacher was 1 of the 2 in the school who was unvaccinated). The symptoms were attributed to allergies, leading to the delayed Covid testing 

-- the teacher read aloud in the classroom unmasked, against the school mask requirement 

-- student adherence to masking and distancing were reported to be high in the class 

-- 194 of the 205 students, 21 of 24 staff members, and 16 parents and siblings were all Covid tested (all were encouraged to be tested) 

-- at the time of the outbreak, 72% of eligible persons were fully vaccinated in the city where the school was located

 

Results: 

-- on May 23, 27 Covid cases were reported among staff, students, parents and siblings of those in school 

-- of the 27 cases: 

    -- 12 of the teacher’s students had positive SARS-CoV-2 tests (55%) of the total of 24 in the class (though only 22 of them were tested for SARS-CoV-2), all students were too young for vaccination

    -- attack rate by seating location (all desks were separated by 6ft): 

        --in the 2 rows nearest the teacher: 8 of 10 (80%) were infected 

        --in the back 3 rows: 4 of 14 (28%) were infected (p=0.036 for difference); those symptomatic had mostly: fever (41%), cough (33%), headache (26%) and sore throat (26%) 


    -- here is a diagram of the classroom , noting the infected teacher and which students were then infected (symptomatic in colored boxes, asymptomatic in blue lined squares)

 

 

 

 

-- 18 had whole genome sequencing, all detecting the Delta variant 

    -- 22 of the 27 cases (81%) had symptoms 

-- from May 24-June 1, 6 of 18 students in a separate grade of students who were 3 years older at the school had positive results; 8 additional Covid cases were found in parents and siblings in these 2 grades. The 2 classrooms were separated by a large courtyard. All classrooms had HEPA air filters and doors/windows were left open. One of the students had 2 classmates for a sleepover and all got symptomatic Covid 

    --3 cases were in people fully vaccinated, in siblings or parents of the Covid cases in the index patients’ classes 

-- cases were also identified in one student each from 4 different grades, 3 were symptomatic 

-- 4 parents were also infected, one of whom was not vaccinated, all symptomatic (3 of the total of 8 infected parents and siblings were fully vaccinated) 

-- genetic testing found that the same virus was found in 6 students from the index teacher (though the teacher did not have genetic testing), 4 were from students in a separate grade, and one was from a sibling on an index patient

    -- 3 of the 5 community cases found later had indistinguishable genetic sequencing vs in the school outbreak 

 

Commentary: 

-- it seemed that the infected teacher was associated with widespread infection in the class with an attack rate of about 50%, notably with decreased cases in students who were further from the teacher. Other students were also infected, in part from being siblings of infected index students and in part from likely in-school association. Some parents of the infected children were also infected. Many of the adults infected were vaccinated. All Covid patients had mild cases/none hospitalized. 

-- so, pretty widespread infection from one individual teacher in the school, with symptomatic and asymptomatic infections, in vaccinated and unvaccinated adults.  

    -- though transmission risk was much lower in those vaccinated vs unvaccinated (esp in the nonvaccine-eligible children in the classrooms) 

-- these cases involved the highly transmissible Delta variant; vaccine is effective but risk of transmission remains 

-- this school was notable for their aggressive covid mitigation approaches, with good HEPA filter ventilation, open windows/doors to decrease stagnant air further, distancing of the children, mask wearing (except this teacher..., and likely that these young ones did not have optimal masking.  it seems that these mitigation strategies were indeed effective, since this highly transmissible virus was more often transmitted to the students closest to this unmasked yet infected teacher)

-- one comment on the teacher waiting 2 days to get covid tested: I think there is such Covid ennui that many people with mild symptoms are not getting tested, and that as we migrate into the increased viral infections of the fall/winter (rhinovirus, rsv, flu, etc), even more people will just ignore symptoms, falsely attributing them to allergies (as per the teacher above) or a mild viral illness. 

    --As it is, fewer people are getting tested now, so our understanding of the epidemiology of the Delta variant is somewhat compromised, especially in light of the pretty high numbers of vaccinated people who will get only mild or asymptomatic infections (not being tracked by the CDC) and who may be even more dismissive of getting tested because they feel that they are protected from Covid.

-- it should be remembered that long covid happens pretty frequently (not infrequently with disabling long term symptoms in adults and also in kids, many with mild symptoms or even asymptomatic:  https://gmodestmedblogs.blogspot.com/2021/08/covid-long-covid-update-including-in.html 

-- see http://gmodestmedblogs.blogspot.com/2021/01/covid-low-transmission-rates-in-schools.html for study in Wisconsin finding low SARS-CoV-2 transmission in schools using petty aggressive mitigation strategies in the pre-Delta variant era

Limitations: 

-- we do not have detailed information about the use of masks by the students or the quality of their donning (though the teacher's was clearly doffed...)

-- the index teacher’s SARS-CoV-2 was not available for genetic testing, limiting more definitive interpretation of the chain of events (though it was presumably the same virus as in the bigger cluster in the classroom, given the timing and epidemiology of the events) 

-- testing of parents and siblings was self-directed and happened outside of the school (ie, there could have been more cases) 

-- we do not have good community data on the infection rate, including mildly symptomatic and asymptomatic cases (the largest group), given lack of systematic testing and the CDC's decision not to track these folks

 

So, these studies reinforce the importance of vaccination of teachers: 

-- it is pretty clear that staff are a major vector in transmission to kids in schools, and that the kids can then infect those in their household (eg, see https://gmodestmedblogs.blogspot.com/2021/08/covid-secondary-transmission-from-kids.html )

-- kids are less likely to infect the staff/others than adults are. Part of this may be that kids are less around others (not going out shopping, to bars, etc). part may be due to physiologic differences that may be important:

    -- for example, there is a stepwise increase in nasal ACE-2 levels as kids progress from <10 to age 24 (see https://jamanetwork.com/journals/jama/fullarticle/2766524 ), though ACE-2 levels correlate more with getting infection than with nasal carriage of the virus, and nasal carriage rates are still high in kids (see http://gmodestmedblogs.blogspot.com/2020/08/covid-kids-as-vectors-school-closure.html ). 

    -- but asymptomatic people (which likely includes more kids with their lower ACE-2 levels, the portal of virus entry into the body, since they are less likely to get the Covid disease) would also be less likely to transmit the virus (less coughing??). see https://wwwnc.cdc.gov/eid/article/27/4/20-4576_article . this study is pre-Delta, and i have not seen anything in the Delta era

-- many are too young for the vaccine (though there are comments that Pfizer will release data soon on vaccine efficacy/adverse events in younger children). Vaccination of children will likely be a huge benefit in decreasing in-school SARS-CoV-2 transmission 

    -- and kids still do sometimes get very sick and some die (ie vaccine also likely protects them as well)

-- this study suggests that the usual mitigation strategies (masks, distancing) are still important. And perhaps that schools unable to provide appropriate distancing have reduced classroom sizes (which might entail continuing with in-school shifts for students, maybe even with more in-home teaching continuing, though the clear preference is in-school teaching) 

 

So from a societal perspective, I do not see any reason why there should not be a vaccination mandate for teachers/other school workers at all levels. This study and others scream for this mandate (though would have been much better months ago, prior to schools reopening....) And masks should be required (the huge outbreak in Florida now, where the vaccination rates are moderate for the US, suggest that the lack of vaccine mandates by the governor or mandated mitigation strategies (eg masks, the latter negated in the courts…🙂🙂) was in fact as stupid as predicted and likely a major source of the Delta conflagration there (also with the complete opening and normalization of bars, events, restaurants). And so many studies have shown these mitigation strategies are helpful: one recent though pre-Delta variant one: https://www.cdc.gov/mmwr/volumes/70/wr/mm7035e3.htm?s_cid=mm7035e3_e&ACSTrackingID=USCDC_921-DM64558&ACSTrackingLabel=MMWR%20Early%20Release%20-%20Vol.%2070%2C%20August%2027%2C%202021&deliveryName=USCDC_921-DM64558 ) , or https://www.nytimes.com/2021/08/02/us/covid-schools-delta-variant.html and https://pediatrics.aappublications.org/content/147/4/e2020048090 


geoff


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