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1. 'RIVM launches study on coronavirus herd immunity'

While herd immunity is not the official Dutch strategy @rivm launched an investigation into the development of herd immunity in all Dutch age groups, including children.

rivm.nl/node/154191
2. This large-scale research project, into this apparently desired side effect, commenced as of March 31 and was approved by the medical ethics review committee of Utrecht (MEC-U). Several screening rounds have been scheduled.

rivm.nl/sites/default/…
3. After each round @rivm will have learned more about the development of herd immunity in the Dutch population. In addition this research project, is meant to determine the life-time and quality of the SARS-CoV-2 antibodies.
4. This will answer the question whether the Dutch population is able to withstand a 2nd infection in the longer term. This @rivm herd immunity study will take 18 months in total. However, a research project generally ends with the conclusion that further research is needed.
5. In other words the Dutch strategy is a long-lasting experiment into the development of herd immunity, with regards to COVID-19, within the Dutch population. @rivm has claimed that the 1st results were to be expected in May.
6. So far, and as far as I know, no results have been presented by the @rivm, regarding this large-scale herd immunity research project, embedded within the PIENTER research program. The 'Research COVID-19 in the Netherlands' weblink refers to an ominous sign:
7. @rivm claims that the preliminary results for the first round (April) have been presented to the Outbreak Management Team and the Dutch parliament, these preliminary results can be found here:

rivm.nl/pienter-corona…
8. The enthusiasm for this research project was limited, of the 6102 invited participants, 3400 persons participated (55.7%). The age of the participants varies between 3 and 90 years old.
9. However only 2096 blood samples were investigated, indicating that 1304 participants did not actually submit a blood sample. The actual participation degree in April was therefore only 34.4%.
10. Only 75 persons (3.6%) had detectable amounts of SARS-CoV-2 antibodies in their blood. The persons with detectable amounts of anti-bodies reported COVID-19 symptoms more often as compared to persons who did not have SARS-CoV-2 antibodies, which is rather obvious.
11. But I suspect that the @rivm wants to leave some space, in order to claim the seronegative people are indeed immune, at a later date, e.g., due to T-cells or detection limit thresholds.
12. The @rivm states on the aforementioned herd immunity research result webpage:

"We are very curious what this picture will look like after the second round.",

referring to the herd immunity progress indicator chart shown above.
13. Special thanks go out to Lena (@boisei0) for retrieving the RIVM herd immunity results webpage.
14. Dutch parliament was indeed made aware of the herd immunity research results during a technical briefing on April 22. However, the results where presented in the context of children and the spread of COVID-19 (slide 21).

tweedekamer.nl/downloads/docu…
15. The herd immunity research results indicated that of the persons below the age of 20 only 1% had developed SARS-CoV-2 antibodies. While of the persons over 20 year of age 4.2% had developed these antibodies.
16. Combined with the Utrecht School study and, a probably very biased literature study, these results were the basis for the conclusion that children hardly transmit the SARS-CoV-2 virus and that it was OK to re-open the primary schools and later the secondorary schools.
17. Slide 22, suggests that there is a report regarding the 1st herd immunity research results, as it mentions the following publication: F van der Klis et al, IIV-CIb/RIVM.
18. The 1st author is Fiona R.M. van der Klis a researcher at the Immunology of Infectious Diseases and Vaccines (IIV) department of the National Institute for Public Health and the Environment (RIVM).
19. Fiona van der Klis is the principal investigator with regards to this herd immunity research embedded within the PIENTER research program. The report IIV-CIb/RIVM seems to be unavailable.

rivm.nl/pienter-onderz…
20. Serology wise the below 20 years of age groups are under-represented. When herd immunity is an objective, or a side effect, of the Dutch 'intelligent control' strategy. The decision to re-open the schools may primarily be driven by this observed under-representation.
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Jorrit Posthuma de Boer
@JPosthumadeBoer
@ContainmentNow @Sabje1979 Shown in the figure below is the number of SARS-CoV-2 PCR positive cases versus the number of hospitalizations. In the Netherlands there would be hardly a delay between testing and hospitalization because of the restricted testing policy. Testing meant going to hospital.
@ContainmentNow @Sabje1979 In the figure the week numbers are indicated. Prior to the peek in hospitalizations (week 13), a constant fraction (hospitalizations : positive cases) of 0.49 is observed (green line).
@ContainmentNow @Sabje1979 After week 13 this ratio declines to 0.13 in week 15 and remains constant thereafter (red line). This means that the number of hospitalizations per positive case reduced by a factor 4 in week 15.
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Jorrit Posthuma de Boer
@JPosthumadeBoer
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 >>

1.
in countries that employed a track-trace-isolate policy in order to suppress the spread of the SARS-CoV-2 virus.

2.
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.

3.
Read 52 tweets
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Jorrit Posthuma de Boer
@JPosthumadeBoer
De rol van kinderen in de transmissie van SARS-CoV-2

Omdat dit onderzoek steeds weer blijkt op te duiken, plaats ik enkele kanttekeningen bij dit artikel.
ntvg.nl/artikelen/de-r…
De onderzoeksvraag die in dit artikel wordt gesteld is:

"Nagaan of kinderen een rol spelen in de overdracht van SARS-CoV-2 naar andere kinderen en volwassenen, en inzicht krijgen in symptomatische en asymptomatische infecties bij kinderen."
Het onderzoek berust op 2 datasets. De eerste dataset betreft geregistreerde Covid19 positief getesten aanwezig in de Osiris database van het RIVM (t/m 13 mei 2020), aangevuld met bron- en contact onderzoek uit de HPZone database van de GGD's (t/m 2 april 2020).
Read 36 tweets

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