COVID: low viral transmission in daycare

 A French study found that the incidence and transmissibility of SARS-CoV-2 was quite low in children in daycare centers (see covid daycare low transmission lancetchildadol2021 in dropbox, or https://www.thelancet.com/action/showPdf?pii=S2352-4642%2821%2900024-9)

 

Details:

-- 327 children and 197 staff working in daycare centers that remained open for essential workers’ children during a nationwide lockdown in France, as well as a comparator group of 164 adults, between June 4 and July 3, 2020

    -- 22 daycare centers were assessed, 20 in Paris area, one in Annecy and one in Rouen

    -- at that time, SARS-CoV-2 infection rate in the general population in Paris was 10%

-- children: mean age 1.9, range 5 months to 4.4 years

    -- there were special precautions in these daycare centers open during the lockdown, including: smaller, defined groups of children and staff; systematic measurement of body temperature; exclusion of children who became feverish or ill; and reinforced hygiene and distancing measures

        -- 8-56 children attended each of the centers during the lockdown (median 24)

-- staff: mean age 40, 99% women

-- comparator group: hospital workers not exposed to Covid patients (administrators and lab staff): mean age 43, 77% women

    -- they had a comparator group in order to control for exposure in places other than the household (traveling to work, overall hospital environment), since those in the comparator group had similar but distinct occupational backgrounds and continue to work during the lockdown.

-- serologic testing was performed with the Biosynex COVID-19 Ag BSS rapid chromatographic immunoassay (which tests both for IgM and IgG antibodies)

    -- manufacture's data: sensitivity 91.8%, specificity 99.2%

-- primary outcome: SARS-CoV-2 seroprevalence in the 3 groups; secondary outcomes were the proportion of children with positive nasopharyngeal swabs and stool swabs for SARS-CoV-2

-- exploratory outcome: factors associated with SARS-CoV-2 infection in the children or the adults (sex, age, medical history, history of symptoms, PCR testing, composition of the family, contact with confirmed or suspected Covid cases, number of days of attendance at work, occupations of children’s parents, occupation of adult participant’s partners, and serologic status of parents)

 

Results:

-- positive serologic tests: 14 children and 14 daycare staff

    -- raw seroprevalence: children 4.3% (2.1%-7.1%), staff 7.7% (4.2%-11.6%)

    -- calculated seroprevalence, accounting for the imperfect sensitivity and specificity of the assay used:

        -- children: 3.7% (1.3%-6.8%)

        -- daycare staff: 6.8% (3.2%-11.5%)

-- comparator group: 9 people with positive tests: leading to a calculated seroprevalence of 5.0% (1.6%-9.8%)

-- none of the 197 nasal swabs and none of the 261 rectal swabs from the children were PCR-positive

-- exploratory analysis:

    -- 49 seropositive vs seronegative children had at least one seropositive parent:  6 (55%) of 11 vs 22 (14%) of 149, RR 6.1 (1.9-19.1) [ie, likely lots of transmission from parents to kids]

    -- children attending a daycare center with at least one positive staff member had no significant increase in being seropositive, RR 1.9 (0.7-5.8) [ie, likely no significant transmission from staff to kids]

    -- there was no increase in the risk of contracting Covid following exposure to a child with laboratory-confirmed Covid. But the relative risk following contact with an adult Covid case in the household was 13-fold, RR 13.1 (0.8-221.1)

    --6 (43%) of the children were exposed to an adult household member with laboratory-confirmed Covid vs 19 (6%) of 307 seronegative children.

    -- seropositive vs seronegative children, had sevenfold risk of having an adult household member with laboratory confirmed Covid, relative risk of 7.1 (2.2-22.4)

    -- the 14 seropositive children did not cluster: they came from 13 different daycare centers, and the 2 in a single center were in different areas of the center

-- of note, the presence of clinical signs during lockdown and exclusion from day care centers was not associated with seropositivity

-- comparator group: seropositive adults were more likely than seronegative adults to been exposed to another adult living in the household with confirmed Covid, RR 17.2 (2.1-140.8)

    -- the comparator group had similar seroprevalence to the daycare center staff

 

Commentary:

-- the study found that the risk of transmission of SARS-CoV-2 was very low from children in daycare. For example, there was no increased risk for daycare center staff from getting Covid from a child with PCR-confirmed Covid, during a lockdown period in France (and none of the kids were PCR-positive on nasal or rectal eval)

-- compared with children who tested negative, those who tested positive were six times more likely to have a parent who tested positive. Among staff members, there was no increase in SARS-CoV-2 infection risk after exposure to a child with confirmed COVID-19, but the risk was increased 13-fold when they lived with an adult with COVID-19.

    -- and the overall seroprevalence in children in the daycare centers (3.7%) was about 1/3 that found in the Paris region (10%) and 1/2 of nationwide (7%); but the seroprevalence rate among the adult participants was similar to the general population

    -- this finding was similar to what was found in daycare studies in the US: daycare workers in centers remaining open had no higher risk of Covid than those in centers that had closed (though a study from Salt Lake City in 7yo kids did suggest transmission from kids to adults, but in the setting of less aggressive infection control than in the French study above). see http://gmodestmedblogs.blogspot.com/2020/09/covid-transmission-from-kids-to-adults.html

-- prior studies have suggested that children <18yo account for 1-8% of laboratory confirmed Covid-19 cases and 2-4% of those admitted to the hospital. There are not much data on those 0-3yo

-- early concerns were that children were more likely to be asymptomatic and be vectors for SARS-CoV-2 to those at home who might be at higher risk

    -- this concern led to aggressive school and daycare closings early on

-- this article parallels the recent study finding very low risk of infection/viral transmission from kids in schools (see http://gmodestmedblogs.blogspot.com/2021/01/covid-low-transmission-rates-in-schools.html )

Limitations:

-- these daycare centers did have strict sanitary precautions, including limited numbers of children, which decreases the generalizability of these results to the broader community (though there was no measurement in the study of adherence to these measures)

-- much of these results rely on antibody testing, with inherent inaccuracies (including a sensitivity of only 92%, though high specificity of 99%), and reflects a retrospective look at prior infections (the granular data are likely less accurate than in prospective trials)

 

So, overall, the study was reassuring that young children need not be considered a major SARS-CoV-2 vector, and that intrafamily viral transmission was significantly higher than within daycare centers

-- there was no clear transmissibility from a young one to a worker and vice versa

    --but, it is likely that there needs to be aggressive infection control, as in the French study to achieve this

-- this French study also confirmed that following clinical signs for early infection was not particularly useful (eg: we know that presymptomatic people can have very transmissible infections)

-- it also suggests that contact tracing and screening tests are especially useful for adult household members and staff, with less clear utility of testing all children in the daycare center

-- these results are concordant with the recently released guidelines from the CDC that K-12 schools should be reopened, along with a detailed plan (see https://www.nytimes.com/2021/02/12/health/school-reopenings-cdc.html and https://www.cdc.gov/coronavirus/2019-ncov/downloads/community/schools-childcare/K-12-Operational-Strategy-2021-2-12.pdf?CDC_AA_refVal=https%3A%2F%2Fwww.cdc.gov%2Fcoronavirus%2F2019-ncov%2Fcommunity%2Fschools-childcare%2Foperation-strategy.html

so, the focus should be on vaccinating adults, contact tracing/screening, keeping kids in schools and daycare (with the appropriate infection precautions of distancing, masks, etc) and thereby reestablishing their important educational and social interactions, and also freeing up adults from taking care of their kids during this pandemic and getting back to their jobs and normal social interactions to the extent possible (with immunization and appropriate infection precautions)...

geoff

 

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