Evaluation of literature used to motivate the re-opening of Dutch primary schools during the Covid-19 pandemic
The Dutch decision to partially re-open primary schools as of 11 may 2020, and to fully re-open them as of June 10, was partly motivated by studies performed >>
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The Dutch decision to partially re-open primary schools as of 11 may 2020, and to fully re-open them as of June 10, was partly motivated by studies performed >>
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in countries that employed a track-trace-isolate policy in order to suppress the spread of the SARS-CoV-2 virus.
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There may be some caveats when conclusions are drawn from these studies, with regards to the susceptibility to and transmission of the SARS-CoV-2 virus among different age cohorts, and children in particular.
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These studies were referenced in the paper: Hoek, van der, W. et al., “De rol van kinderen in de transmissie van SARS-CoV-2” (“The role of children in the transmission of SARS-CoV-2”), that formed the main, if not only, source for that decision.
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ntvg.nl/artikelen/de-r…
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ntvg.nl/artikelen/de-r…
Spread of SARS-CoV-2 in the Icelandic Population
The aim of this study was to provide a view of how the SARS-CoV-2 virus spread in the Icelandic population (366,130), while early and aggressive track-trace-isolate measures were implemented.
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nejm.org/doi/full/10.10…
The aim of this study was to provide a view of how the SARS-CoV-2 virus spread in the Icelandic population (366,130), while early and aggressive track-trace-isolate measures were implemented.
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nejm.org/doi/full/10.10…
Although this study was not aimed at investigating the role of children in the spread of the SARS-CoV-2 virus, the following passage (translated) based on this study ends up in the pivotal Dutch article:
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“Many SARS-CoV-2 PCR tests were performed in Iceland in relation to the population size. Icelandic children under 10 years of age were less likely to have a positive PCR result for SARS-CoV-2 as compared to children ≥ 10 years of age (6.7% vs. 13.7%)." >>
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"In a random sample of 10,797 persons (3% of the population) none of the children <10 years old had a positive PCR result; the prevalence in persons aged 10-19 years was 0.3% and in 40-49 year olds 1.5%.”
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Background Information
The 1st case, a male returning on February 22 from Northern Italy, was diagnosed after developing symptoms at February 28. Austria, Italy and Switzerland were declared a high risk area on February 29.
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The 1st case, a male returning on February 22 from Northern Italy, was diagnosed after developing symptoms at February 28. Austria, Italy and Switzerland were declared a high risk area on February 29.
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Residents of Iceland who arrived from these high risk areas were required to go into quarantine. On March 2 there were 9 confirmed infections, all patients were in the range of 40 to 70 years of age.
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On March 3 sanctions were announced for those who would break quarantine. The first 4 cases of local transmissions were identified on March 6 (45 confirmed infections, 4 domestic infections).
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On March 13 (134 confirmed infection, 30 domestic infections, 1097 in quarantine, and 129 in isolation), the announcement was made that, as of March 16, universities and secondary schools would be closing for 4 weeks.
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In addition a ban on public gatherings of over 100 was put in place. Elementary schools and pre-schools remained open, although restrictions were in place: (1) limited class sizes; (2) “bubble” strategy, a division of classes into non-interacting discrete units; and >>
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(3) social distancing of 2 m by teachers within these schools. As of March 18, the whole world was defined a high risk area. From March 25, a nation-wide ban on public assemblies over 20 and on visits to nursing homes and hospitals took effect.
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All swimming pools, museums, libraries and bars closed, as did any businesses requiring a proximity of less than 2 m (hairdressers, tattoo artists, etc.). Self-isolation for the elderly and other groups at increased risk was promoted.
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In addition regional measures were taken. On March 21 in Vestmannaeyjar (South Iceland: 179 infections till June 14) assemblies with more than 10 persons were prohibited.
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For the Húnaþing vestra district (Northwest Iceland: 35 infections till June 14) all inhabitants were ordered to stay at home except to buy necessities.
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SARS-CoV-2 Testing
Targeted PCR testing started as of January 31 and was performed on residents who: (1) were symptomatic (cough, fever, body aches, and shortness of breath); (2) had travelled to high-risk countries; or (3) had contact with infected persons.
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Targeted PCR testing started as of January 31 and was performed on residents who: (1) were symptomatic (cough, fever, body aches, and shortness of breath); (2) had travelled to high-risk countries; or (3) had contact with infected persons.
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Population screening (March 13 – April 1) open to all residents of Iceland who were not quarantined, was carried out by issuing an open invitation to 10,797 persons and sending random invitations to 2,283 persons of 20 to 70 years of age (April 1 – April 4).
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All PCR samples were collected by nasopharyngeal and oropharyngeal swaps. The testing and screening procedures are outlined in the figure below.
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Contact Tracing, Self-isolation and Quarantine
Individuals with a positive PCR test were required to self-isolate for at least 14 days, until 7-10 days after fever had subsided or until they had a negative PCR test.
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Individuals with a positive PCR test were required to self-isolate for at least 14 days, until 7-10 days after fever had subsided or until they had a negative PCR test.
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In addition these persons were contacted by phone to track their infection. Questions related to symptoms, symptom onset, recent travels, and previous contacts with infected persons were asked (24h before 1st symptoms).
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All registered contacts were interviewed by telephone, asked about their symptoms, and were required to go into self-quarantine for 14 days. Those with symptoms and those in whom symptoms developed in self-quarantine were tested for SARS-CoV-2.
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Results
The summary of results is given in the table below. The percentage of infected participants (population screening) remained stable for the 20-day duration of screening (see figure below).
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The summary of results is given in the table below. The percentage of infected participants (population screening) remained stable for the 20-day duration of screening (see figure below).
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The percentage asymptomatic patients varied between 41% - 54% in population screening, being highest in the random one.
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These results are consistent with a slow spread of SARS-CoV-2 through the Icelandic population, a finding that indicates that the containment measures have worked.
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However, the virus had spread to such an extent that without test and isolate, track contacts, and quarantine, the virus wouldn’t have been contained.
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Of the 564 children under the age of 10 years in the targeted testing group, 38 (6.7%) tested positive, in contrast to positive test results in 1183 of 8635 persons who were 10 years of age or older (13.7%).
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Analysis involving participants up to 20 years of age, showed a gradual increase with older age in the percentage who tested positive. In the population-screening group, the difference was even more marked: none of the 848 children under the age of 10 years tested positive.
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These results suggested that young children were less likely to test positive for SARS-CoV-2 as compared to adolescents or adults. Whether the lower incidence of positive results resulted from less exposure to the virus or from biologic resistance was not known.
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Evaluation
While the percentage of infected participants remained fairly constant, the age distribution of infected participants changed considerably.
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While the percentage of infected participants remained fairly constant, the age distribution of infected participants changed considerably.
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On March 2 there were 9 confirmed infections, all patients were 40-70 years of age, these ages continued to dominated infections at March 13. As of March 23 the number of infections had spread-out over the 20 to 70 years of age groups, approaching the March 31 distribution.
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The initial over-representation of the 40 to 70 years of age group, caused this group to be the major source of infections. This is also the group that likely does not have a significant amount of children in the primary school age.
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Until March 14 travel was the major source of infections, however most did not contribute to further transmissions, as most travellers from high risk areas were tested and isolated or quarantined.
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Family, social and work contacts were mainly responsible for transmissions into the initially under-represented age groups. This will already have caused a delay before the under-represented age groups, having children in the primary school age, could be infected.
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Subsequent infections of children through their parents, the most likely source based on the higher virus prevalence in that age group, are therefore delayed. Before symptoms show within children even more time would have passed.
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In other words, in Iceland, due to the initial distribution of infections over the population, infections in children in the primary school age are not to be expected early on.
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The fact that persons with a PCR identified infection were placed in isolation and identified contacts were quarantined means that transmission chains were relatively short and quickly broken-up.
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In the period March 13-31, 52% of the individuals who tested positive were already in quarantine. This likely has contributed to the fact that not many children were found positive, as parents would have been made aware of the risk of transmission.
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In addition this quarantining will already have limited the spread within and between age groups, i.e., it tends to stabilize the distribution of infections over different age groups.
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A further complication in identifying the role of children in transmissions arises from the dependence of incubation time with age, the incubation time is lower for parents as compared to children.
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onlinelibrary.wiley.com/doi/full/10.10…
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onlinelibrary.wiley.com/doi/full/10.10…
This may cause wrong assignments of the index patient. The parent, being already the most probable source of infection based on the observed age distribution, is more likely to show symptoms first, when parents and children are infected at approximately the same time.
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In this study the index patient was not indicated, but is however implied, as the type of exposure was determined in contact-tracing. Therefore the assignments ‘work’ (including school transmissions) and ‘family’ may not always be right.
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In the distribution of SARS-CoV-2 infections over age cohorts, primary school children were initially under-represented in Iceland. When looking at the evolution of infections over the period March 13 until March 31, a growth in infections of 11-5 to 12.5% is observed.
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That is not significantly different from the growth observed in other age cohorts (mean: 11.2 ± 5.7). It is lower than the highest growth of 23.4% observed for the 30-39 age cohort, but not substantially different from other age cohorts.
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Therefore based on the data of Iceland there is no evidence that children are less susceptible or transmit the virus to a lower extend.
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As measures were in place to reduce transmissions within primary schools most transmissions likely occurred within the family, where parents were the likely primary source based on the distribution of SARS-CoV-2 infections over the age cohorts.
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However, the observed growth rate indicates children are as susceptible as any other age-group.
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Sub-conclusions
This study does not provide enough data to assess the transmissibility of the virus among primary school children.
The pandemic in Iceland may have been contained too quickly, before any transmission among primary school children was visible.
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This study does not provide enough data to assess the transmissibility of the virus among primary school children.
The pandemic in Iceland may have been contained too quickly, before any transmission among primary school children was visible.
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* 11-5 = 11.5
* Growth as indicated in the table is not in %, it is just the end value divided by the begin value
