Symptomatic, Presymptomatic, and Asymptomatic Transmission of SARS-CoV-2

Importance: Asymptomatic and presymptomatic carriers of SARS-CoV-2 are an ongoing and significant risk for community spread of the virus, especially with the majority of the world still unvaccinated and new variants emerging. Objective: To quantify the presence and effects of symptom presentation (or lack thereof) on the community transmission ofSARS-CoV-2. Design: A cohort of 12,960 young adults participated in health reporting, contact tracing, and COVID-19 testing for 103 days between August 10 and November 20, 2020. Setting: A mid-sized university campus in Indiana, United States. Participants: University students, most of whom are 18-23 years old (67%) and living in congregate on-campus housing (60%). Of the 12,960 students, 1,556 (12.0%) tested positive for COVID-19 during the 103 day period. Of the positive cases, 1,198 reported sufficient health check data (7 days prior and 7 days post diagnosis) to be classified as asymptomatic or symptomatic. Main Outcome: Secondary attack rate, based on presentation or absence of symptoms and type of symptoms calculated with respect to confirmed close contacts and a 14-day incubation period, varies on the type of symptom, timing of symptoms, and absence of symptoms. A quantifiable understanding of SAR on the longitudinal data of more than one thousand subjects in a university environment provides keen insights about developing strategies to respond to the continued prevalence of COVID-19 in the unvaccinated world and growth of variants. Results: 32.5% of all cases reported no symptoms within a 15-day window centered on their positive test (7 days prior, the day of the positive test, and 7 days after). The secondary attack rate (SAR) of asymptomatic COVID-19 index cases was 19.1%. The SAR of symptomatic index cases was 25.4%, and while the onset timing of symptoms did not affect transmission, the presence of certain symptoms like fever, shortness of breath, and dry cough increased the SAR as high as 30.0%. Conclusions and Relevance: Asymptomatic rates of transmission of SARS-CoV-2 are much higher than has been estimated in prior studies and continue to pose a significant and ongoing risk in the pandemic, especially with the prevalence of variants like the Delta variant. In addition, different symptoms are associated with varying rates of transmission, posing a significant challenge in how to diagnose or assess risk through mechanisms such as daily health checks for symptom reporting, a practice commonly in place for entry into schools, offices, restaurants, etc. Given the uncertain nature of symptoms and varied transmission rates, this study suggests a broader embrace of masking, social distancing and testing might be needed to counter the variants until higher global vaccination rates can be achieved.

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Investigation of Four Clusters of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) in Rwanda, 2020

International Journal of Environmental Research and Public Health ◽

10.3390/ijerph18137018 ◽

2021 ◽

Vol 18 (13) ◽

pp. 7018

Author(s):

Olivier Nsekuye ◽

Edson Rwagasore ◽

Marie Aime Muhimpundu ◽

Ziad El-Khatib ◽

Daniel Ntabanganyimana ◽

...

Keyword(s):

High Risk ◽

Severe Acute Respiratory Syndrome ◽

Symptom Onset ◽

Attack Rate ◽

Positive Sample ◽

Contact Tracing ◽

Face To Face ◽

Laboratory Confirmation ◽

Closed Environment ◽

Index Cases

We reported the findings of the first Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) four clusters identified in Rwanda. Case-investigations included contact elicitation, testing, and isolation/quarantine of confirmed cases. Socio-demographic and clinical data on cases and contacts were collected. A confirmed case was a person with laboratory confirmation of SARS-CoV-2 infection (PCR) while a contact was any person who had contact with a SARS-CoV-2 confirmed case within 72 h prior, to 14 days after symptom onset; or 14 days before collection of the laboratory-positive sample for asymptomatic cases. High risk contacts were those who had come into unprotected face-to-face contact or had been in a closed environment with a SARS-CoV-2 case for >15 min. Forty cases were reported from four clusters by 22 April 2020, accounting for 61% of locally transmitted cases within six weeks. Clusters A, B, C and D were associated with two nightclubs, one house party, and different families or households living in the same compound (multi-family dwelling). Thirty-six of the 1035 contacts tested were positive (secondary attack rate: 3.5%). Positivity rates were highest among the high-risk contacts compared to low-risk contacts (10% vs. 2.2%). Index cases in three of the clusters were imported through international travelling. Fifteen of the 40 cases (38%) were asymptomatic while 13/25 (52%) and 8/25 (32%) of symptomatic cases had a cough and fever respectively. Gatherings in closed spaces were the main early drivers of transmission. Systematic case-investigations contact tracing and testing likely contributed to the early containment of SARS-CoV-2 in Rwanda.

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Contact Tracing of COVID-19 in Karnataka, India: Superspreading and Determinants of Infectiousness and Symptomaticity

10.1101/2020.12.25.20248668 ◽

2020 ◽

Author(s):

Mohak Gupta ◽

Giridara G Parameswaran ◽

Manraj S Sra ◽

Rishika Mohanta ◽

Devarsh Patel ◽

...

Keyword(s):

Symptom Onset ◽

Attack Rate ◽

Clinical Severity ◽

Contact Tracing ◽

Significant Heterogeneity ◽

Symptomatic Infection ◽

Individual Level ◽

Serial Interval ◽

Index Cases ◽

Degree Of Heterogeneity

Brief AbstractWe analysed SARS-CoV-2 surveillance and contact tracing data from Karnataka, India up to 21 July 2020. We estimated metrics of infectiousness and the tendency for superspreading (overdispersion), and evaluated potential determinants of infectiousness and symptomaticity in COVID-19 cases. Among 956 cases confirmed to be forward-traced, 8.7% of index cases had 14.4% of contacts but caused 80% of all secondary cases, suggesting significant heterogeneity in individual-level transmissibility of SARS-CoV-2 which could not be explained by the degree of heterogeneity in underlying number of contacts. Secondary attack rate was 3.6% among 16715 close contacts. Transmission was higher when index case was aged >18 years, or was symptomatic (adjusted risk ratio, aRR 3.63), or was lab-confirmed ≥4 days after symptom onset (aRR 3.01). Probability of symptomatic infection increased with age, and symptomatic infectors were 8.16 times more likely to generate symptomatic secondaries. This could potentially cause a snowballing effect on infectiousness and clinical severity across transmission generations; further studies are suggested to confirm this. Mean serial interval was 5.4 days. Adding backward contact tracing and targeting control measures to curb super-spreading may be prudent. Due to low symptomaticity and infectivity, interventions aimed at children might have a relatively small impact on reducing transmission.Structured AbstractBackgroundIndia has experienced the second largest outbreak of COVID-19 globally, yet there is a paucity of studies analysing contact tracing data in the region. Such studies can elucidate essential transmission metrics which can help optimize disease control policies.MethodsWe analysed contact tracing data collected under the Integrated Disease Surveillance Programme from Karnataka, India between 9 March and 21 July 2020. We estimated metrics of disease transmission including the reproduction number (R), overdispersion (k), secondary attack rate (SAR), and serial interval. R and k were jointly estimated using a Bayesian Markov Chain Monte Carlo approach. We evaluated the effect of age and other factors on the risk of transmitting the infection, probability of asymptomatic infection, and mortality due to COVID-19.FindingsUp to 21 July, we found 111 index cases that crossed the super-spreading threshold of ≥8 secondary cases. R and k were most reliably estimated at R 0.75 (95% CI, 0.62-0.91) and k 0.12 (0.11-0.15) for confirmed traced cases (n=956); and R 0.91 (0.72-1.15) and k 0.22 (0.17-0.27) from the three largest clusters (n=394). Among 956 confirmed traced cases, 8.7% of index cases had 14.4% of contacts but caused 80% of all secondary cases. Among 16715 contacts, overall SAR was 3.6% (3.4-3.9) and symptomatic cases were more infectious than asymptomatic cases (SAR 7.7% vs 2.0%; aRR 3.63 [3.04-4.34]). As compared to infectors aged 19-44 years, children were less infectious (aRR 0.21 [0.07-0.66] for 0-5 years and 0.47 [0.32-0.68] for 6-18 years). Infectors who were confirmed ≥4 days after symptom onset were associated with higher infectiousness (aRR 3.01 [2.11-4.31]). Probability of symptomatic infection increased with age, and symptomatic infectors were 8.16 (3.29-20.24) times more likely to generate symptomatic secondaries. Serial interval had a mean of 5.4 (4.4-6.4) days with a Weibull distribution. Overall case fatality rate was 2.5% (2.4-2.7) which increased with age.ConclusionWe found significant heterogeneity in the individual-level transmissibility of SARS-CoV-2 which could not be explained by the degree of heterogeneity in the underlying number of contacts. To strengthen contact tracing in over-dispersed outbreaks, testing and tracing delays should be minimised, retrospective contact tracing should be considered, and contact tracing performance metrics should be utilised. Targeted measures to reduce potential superspreading events should be implemented. Interventions aimed at children might have a relatively small impact on reducing SARS-CoV-2 transmission owing to their low symptomaticity and infectivity. There is some evidence that symptomatic cases produce secondary cases that are more likely to be symptomatic themselves which may potentially cause a snowballing effect on infectiousness and clinical severity across transmission generations; further studies are needed to confirm this finding.FundingGiridhara R Babu is funded by an Intermediate Fellowship by the Wellcome Trust DBT India Alliance (Clinical and Public Health Research Fellowship); grant number: IA/CPHI/14/1/501499.

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Role of children in household transmission of COVID-19

Archives of Disease in Childhood ◽

10.1136/archdischild-2020-319910 ◽

2020 ◽

pp. archdischild-2020-319910 ◽

Cited By ~ 13

Author(s):

Jieun Kim ◽

Young June Choe ◽

Jin Lee ◽

Young Joon Park ◽

Ok Park ◽

...

Keyword(s):

Attack Rate ◽

Index Case ◽

Clinical Findings ◽

International Travel ◽

Contact Tracing ◽

Secondary Case ◽

Household Transmission ◽

Household Members ◽

Index Cases

ObjectiveTransmissibility of COVID-19 by children in the household is not clear. Herein, we describe children’s role in household transmission of COVID-19.Design and settingAll paediatric COVID-19 index cases and their household members reported from 20 January to 6 April 2020 in South Korea were reviewed. The secondary attack rate (SAR) from child index case to household secondary case was calculated. Epidemiological and clinical findings of child index case-household secondary case pair was assessed.ResultsA total of 107 paediatric COVID-19 index cases and 248 of their household members were identified. One pair of paediatric index-secondary household case was identified, giving a household SAR of 0.5% (95% CI 0.0% to 2.6%). The index case was self-quarantined at home after international travel, stayed in her room, but shared a meal table with the secondary case.ConclusionThe SAR from children to household members was low in the setting of social distancing, underscoring the importance of rigorous contact tracing and early isolation in limiting transmission within households.

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A comparison of COVID-19 secondary attack rate in household and close contacts compared to current risk stratification guidelines of the Kerala government

Tropical Doctor ◽

10.1177/00494755211002012 ◽

2021 ◽

pp. 004947552110020

Author(s):

Balram Rathish ◽

Arun Wilson ◽

Sonya Joy

Keyword(s):

High Risk ◽

Risk Stratification ◽

Attack Rate ◽

Low Risk ◽

Contact Tracing ◽

Index Cases ◽

Current Risk ◽

Close Contacts

COVID-19 has been found to be highly infectious with a high secondary attack rate with a R0 of 3.3. However, the secondary attack rate based on risk stratification is sparsely reported, if ever. We studied the contact tracing data for two index cases of COVID-19 with some overlap of contacts. We found that 60% of high-risk contacts and 0% of low-risk contacts of symptomatic COVID-19 patients contracted the infection, in keeping with the Kerala government contact risk stratification guidelines.

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Comparative Household Secondary Attack Rates associated with B.1.1.7, B.1.351, and P.1 SARS-CoV-2 Variants

10.1101/2021.06.03.21258302 ◽

2021 ◽

Author(s):

Kevin A Brown ◽

Semra Tibebu ◽

Nick Daneman ◽

Kevin L Schwartz ◽

Michael Whelan ◽

...

Keyword(s):

Symptom Onset ◽

Attack Rate ◽

Surveillance System ◽

Disease Surveillance ◽

Index Case ◽

Wild Type ◽

Vaccination Rates ◽

Household Contacts ◽

Disease Surveillance System ◽

Index Cases

Background: The emergence of SARS-CoV-2 variants associated with increased transmissibility are driving a 3rd global surge in COVID-19 incidence. There are currently few reliable estimates for the P.1 and B.1.351 lineages. We sought to compare the secondary attack rates of SARS-COV-2 mutations and variants in Canada's largest province of Ontario, using a previously validated household-based approach. Methods: We identified individuals with confirmed SARS-CoV-2 infection in Ontario's provincial reportable disease surveillance system. Cases were grouped into households based on reported residential address. Index cases had the earliest of symptom onset in the household. Household secondary attack rate was defined as the percentage of household contacts identified as secondary cases within 1-14 days after the index case. Results: We identified 26,888 index household cases during the study period. Among these, 7,555 (28%) were wild-type, 17,058 (63%) were B.1.1.7, 1674 (6%) were B.1.351 or P.1, and 601 (2%) were non-VOC mutants (Table 1). The secondary attack rates, according to index case variant were as follows: 20.2% (wild-type), 25.1% (B.1.1.7), 27.2% (B.1.351 or P.1), and 23.3% (non-VOC mutants). In adjusted analyses, we found that B.1.1.7, B.1.351, and P.1 index cases had the highest transmissibility (presumptive B.1.1.7 OR adjusted=1.49, 95%CI 1.36, 1.64; presumptive B.1.351 or P.1 OR adjusted=1.60, 95%CI 1.37, 1.87). Discussion: Substantially higher transmissibility associated with variants will make control of SARS-CoV-2 more difficult, reinforcing the urgent need to increase vaccination rates globally.

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Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Setting-specific Transmission Rates: A Systematic Review and Meta-analysis

Clinical Infectious Diseases ◽

10.1093/cid/ciab100 ◽

2021 ◽

Cited By ~ 5

Author(s):

Hayley A Thompson ◽

Andria Mousa ◽

Amy Dighe ◽

Han Fu ◽

Alberto Arnedo-Pena ◽

...

Keyword(s):

Systematic Review ◽

Severe Acute Respiratory Syndrome ◽

Negative Binomial ◽

Meta Analysis ◽

Contact Tracing ◽

Binomial Model ◽

Transmission Potential ◽

Transmission Rates ◽

Symptom Status ◽

Index Cases

Abstract Background Understanding the drivers of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission is crucial for control policies, but evidence of transmission rates in different settings remains limited. Methods We conducted a systematic review to estimate secondary attack rates (SARs) and observed reproduction numbers (Robs) in different settings exploring differences by age, symptom status, and duration of exposure. To account for additional study heterogeneity, we employed a beta-binomial model to pool SARs across studies and a negative-binomial model to estimate Robs. Results Households showed the highest transmission rates, with a pooled SAR of 21.1% (95% confidence interval [CI]:17.4–24.8). SARs were significantly higher where the duration of household exposure exceeded 5 days compared with exposure of ≤5 days. SARs related to contacts at social events with family and friends were higher than those for low-risk casual contacts (5.9% vs 1.2%). Estimates of SARs and Robs for asymptomatic index cases were approximately one-seventh, and for presymptomatic two-thirds of those for symptomatic index cases. We found some evidence for reduced transmission potential both from and to individuals younger than 20 years of age in the household context, which is more limited when examining all settings. Conclusions Our results suggest that exposure in settings with familiar contacts increases SARS-CoV-2 transmission potential. Additionally, the differences observed in transmissibility by index case symptom status and duration of exposure have important implications for control strategies, such as contact tracing, testing, and rapid isolation of cases. There were limited data to explore transmission patterns in workplaces, schools, and care homes, highlighting the need for further research in such settings.

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Pilot Evaluations of Two Bluetooth Contact Tracing Approaches on a University Campus: Mixed Methods Study (Preprint)

10.2196/preprints.31086 ◽

2021 ◽

Author(s):

Tyler Shelby ◽

Tyler Caruthers ◽

Oren Y Kanner ◽

Rebecca Schneider ◽

Dana Lipnickas ◽

...

Keyword(s):

Mixed Methods ◽

Mobile Phone ◽

Sensitivity And Specificity ◽

Mobile App ◽

Mixed Methods Study ◽

Self Report ◽

Contact Tracing ◽

Free Text ◽

Contact Interactions ◽

University Campus

BACKGROUND Many have proposed the use of Bluetooth technology to help scale up contact tracing for COVID-19. However, much remains unknown about the accuracy of this technology in real-world settings, the attitudes of potential users, and the differences between delivery formats (mobile app vs carriable or wearable devices). OBJECTIVE We pilot tested 2 separate Bluetooth contact tracing technologies on a university campus to evaluate their sensitivity and specificity, and to learn from the experiences of the participants. METHODS We used a convergent mixed methods study design, and participants included graduate students and researchers working on a university campus during June and July 2020. We conducted separate 2-week pilot studies for each Bluetooth technology. The first was for a mobile phone app (“app pilot”), and the second was for a small electronic “tag” (“tag pilot”). Participants validated a list of Bluetooth-identified contacts daily and reported additional close contacts not identified by Bluetooth. We used these data to estimate sensitivity and specificity. Participants completed a postparticipation survey regarding appropriateness, usability, acceptability, and adherence, and provided additional feedback via free text. We used tests of proportions to evaluate differences in survey responses between participants from each pilot, paired t tests to measure differences between compatible survey questions, and qualitative analysis to evaluate the survey’s free-text responses. RESULTS Among 25 participants in the app pilot, 53 contact interactions were identified by Bluetooth and an additional 61 by self-report. Among 17 participants in the tag pilot, 171 contact interactions were identified by Bluetooth and an additional 4 by self-report. The tag had significantly higher sensitivity compared with the app (46/49, 94% vs 35/61, 57%; P<.001), as well as higher specificity (120/126, 95% vs 123/141, 87%; P=.02). Most participants felt that Bluetooth contact tracing was appropriate on campus (26/32, 81%), while significantly fewer participants felt that using other technologies, such as GPS or Wi-Fi, was appropriate (17/31, 55%; P=.02). Most participants preferred technology developed and managed by the university rather than a third party (27/32, 84%) and preferred not to have tracing apps on their personal phones (21/32, 66%), due to “concerns with privacy.” There were no significant differences in self-reported adherence rates across pilots. CONCLUSIONS Convenient and carriable Bluetooth technology may improve tracing efficiency while alleviating privacy concerns by shifting data collection away from personal devices. With accuracy comparable to, and in this case, superior to, mobile phone apps, such approaches may be suitable for workplace or school settings with the ability to purchase and maintain physical devices.

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Increased household secondary attacks rates with Variant of Concern SARS-CoV-2 index cases

10.1101/2021.03.31.21254502 ◽

2021 ◽

Author(s):

Sarah A Buchan ◽

Semra Tibebu ◽

Nick Daneman ◽

Michael Whelan ◽

Thuva Vanniyasingam ◽

...

Keyword(s):

Propensity Score ◽

Attack Rate ◽

Index Case ◽

Population Based ◽

Onset Date ◽

Matched Cohort ◽

Ongoing Research ◽

Health Measures ◽

Private Households ◽

Index Cases

IMPORTANCE: Higher secondary attack rates related to variant of concern (VOC) index cases have been reported, but have not been explored within households, which continue to be an important source of coronavirus disease 2019 (COVID-19) transmission OBJECTIVE: To compare secondary attack rates in households with VOC versus non-VOC index cases. DESIGN: A retrospective cohort study of household index cases reported from February 7-27, 2021. A propensity-score matched cohort was derived to calculate adjusted estimates. SETTING: Ontario, Canada. PARTICIPANTS: A population-based cohort of all private households with index cases. We excluded cases in congregate settings, as well as households with one individual or with >1 case with the same earliest symptom onset date. EXPOSURE: VOC status, defined as either individuals confirmed as B.1.1.7 using whole genome sequencing or those that screened positive for the N501Y mutation using real-time PCR. MAIN OUTCOME AND MEASURE: Household secondary attack rate, defined as the number of household secondary cases that occurred 1-14 days after the index case divided by the total number of household secondary contacts. RESULTS: We included 1,259 index VOC and non-VOC cases in the propensity score-matched analysis. The secondary attack rate for VOC index cases in this matched cohort was 1.31 times higher than non-VOC index cases (RR=1.31, 95%CI 1.14-1.49), similar to the unadjusted estimate. In stratified analyses, the higher secondary attack rate for VOC compared to non-VOC index cases was accentuated for asymptomatic index cases (RR=1.91, 95% CI 0.96-3.80) and presymptomatic cases (RR=3.41, 95%CI 1.13-10.26) CONCLUSIONS AND RELEVANCE: This study provides strong evidence of increased transmissibility in households due to VOCs and suggests that asymptomatic and pre-symptomatic transmission may be of particular importance for VOCs. Our study suggests that more aggressive public health measures will be needed to control VOCs and that ongoing research is needed to understand mechanisms of VOC transmissibility to curb their associated morbidity and mortality.

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Secondary attack rate among high-risk contacts of COVID-19 paediatric index cases: a study at the beginning of the pandemic in Pune city of Western Maharashtra, India

International Journal of Contemporary Pediatrics ◽

10.18203/2349-3291.ijcp20214529 ◽

2021 ◽

Vol 8 (12) ◽

pp. 1920

Author(s):

Ganesh R. Jagadale ◽

Muralidhar P. Tambe ◽

Yallapa Jadhav ◽

Pradip S. Borle ◽

Malangori A. Parande ◽

...

Keyword(s):

Attack Rate ◽

Family Background ◽

Demographic Data ◽

Pediatric Case ◽

Unexplored Area ◽

The Mean ◽

Isolation Facilities ◽

Written Informed Consent ◽

Efficient Transmission ◽

Index Cases

Background: The COVID-19 was the emerging disease caused by SARS-COV2. Efficient transmission of this disease occurs through droplets and fomites. The susceptibility of children to coronavirus disease-19 (COVID-19) and transmission of COVID-19 from children to others is a relatively unexplored area. The aim of this study was to understand the transmission dynamics of severe acute respiratory syndrome coronavirus 2 in children. Study objectives were to estimate secondary attack rate of COVID-19 from paediatric index case during the early phase of pandemic in Pune city and to identify factors associated with transmission and development of the COVID-19 disease.Methods: This was a retrospective cohort study conducted in the month of June 2020. The sample includes 58 contacts of 11 laboratory confirmed pediatric index cases of COVID-19 from Pune municipal corporation after written informed consent. A confidential telephonic interview of parents was taken by using a prestructured questionnaire which includes socio-demographic data, family background, type of house, development of symptoms, outcome etc.Results: The mean age of primary pediatric case was 12.7±5.1 years. All of them were symptomatic. The SAR estimated was 55.2%. The factors significantly affecting SAR were comorbidity, no. of family members, type of family, overcrowding, no. of rooms, bedroom attached with toilet.Conclusions: The household SAR from paediatric patients is high and is closely associated with family size and other household characteristics. Hence, home quarantine should be advocated in smaller families with appropriate isolation facilities; more emphasis is given to co-morbid individuals.

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SARS-CoV-2 circulation in the school setting: A systematic review and meta-analysis

10.1101/2021.09.03.21263088 ◽

2021 ◽

Author(s):

Chiara Martinoli ◽

Carlo La Vecchia ◽

Sara Raimondi ◽

Federica Bellerba ◽

Clementina Sasso ◽

...

Keyword(s):

Systematic Review ◽

Odds Ratio ◽

Meta Analysis ◽

School Setting ◽

Viral Transmission ◽

Contact Tracing ◽

Random Effects Models ◽

Viral Spread ◽

Literature Searches ◽

Index Cases

Background. The contribution of children to viral spread in schools is still under debate. We conducted a systematic review and meta-analysis of studies to investigate SARS-CoV-2 transmission in the school setting. Methods: Literature searches from April, 2021 and repeated on May, 15th 2021 yielded a total of 1088 publications: screening, contact tracing and seroprevalence studies. MOOSE guidelines were followed and data analyzed using random-effects models. Results: From screening studies involving more than 120,000 subjects, we estimated 0.31% (95% Confidence Interval [CI] 0.05-0.81%) SARS-CoV-2 point prevalence in schools. Contact tracing studies, involving a total of 112,622 contacts of children and adults, showed that onward viral transmission was limited (2.54%; 95%CI 0.76-5.31). Young index cases were found to be 74% significantly less likely than adults to favor viral spread (Odds Ratio [OR]=0.26; 95%CI 0.11-0.63) and were less susceptible to infection (OR=0.60; 95% CI 0.25-1.47). Finally, from seroprevalence studies, with a total of 17,879 subjects involved, we estimated that children are 43% significantly less likely than adults to test positive for antibodies (OR=0.57; 95%CI: 0.49-0.68). In conclusion, testing all subjects in schools, independently of symptoms, students less likely than adults favor viral spread and SARS-CoV-2 circulation in schools was found to be limited.

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