sikakoira kirjoitti: ↑Ti Marras 30, 2021 2:22 am
A Danish randomized controlled trial with 6000 participants, published in the Annals of Internal Medicine in November 2020, found no statistically significant effect of high-quality medical face masks against SARS-CoV-2 infection in a community setting
Huoh
No autetaanpa miestä mäessä, kun et selvästikään ymmärrä tai halua ymmärtää kysymystä.
Authors Henning Bundgaard and Kasper Iversen’s response:
” We have been very clear that we studied the efficiency of masks protection for the wearer –
not the effects of face masks when used by an infected individual (source control)”.
Tutkimuksessa oli myös esim. selviä virheitä:
1. When the study was conducted in 30 day period in Denmark about 4,300 people got infected which is about 0.07% of population but the study registerd about 2% infection rate in the 30 day period. The discrepancy by factor of 28 is way too high. Denmark could not have 28 higher infection prevalence than the offcial rate. The multiplier of 28x would imply that by the end of 2020 all adults in Denmark would be infected.
Since the majority of infections in the study were determined by the self-administered antibody tests one must conclude that there was much higher rate of false positives than what the manufacturer of tests claimed.
For this reason the study has a fatal flaw and its conclusiosn should be dismissed.
2. Participants tested themselves for antibodies at baseline and end of intervention using a lateral flow assay.
Antibodies to SARS-CoV-2 develop in symptomatic individuals in the second week after symptom onset and occur later in less severe infections (2, 3). The incubation period is 4-6 days (4). The purpose of mask intervention is to limit exposure to SARS-CoV-2. Yet, seroconversions in the two first weeks of the intervention period may be attributed to SARS-CoV-2 exposures before intervention. The study was conducted in a period of lockdown in Denmark. In the week preceding the first intervention period, 1504 SARS-CoV-2+ cases were identified in 13,940 PCR tests (positive rate: 10.8%); in the last week of the second intervention period 306 cases were identified in 67,773 PCR tests (positive rate: 0.5%). Therefore, a burn-in intervention period before baseline serological testing would have been appropriate.
3. To get a full picture of the masks’ protective effect, an ideal trial should separate the mask group from the non-mask group. If a trial mixes two groups together, their infection rates will be distorted. In other words, the non-mask group’s infection rate will be underestimated because the non-maskers are benefitting from the mask group’s source control, while the mask group’s will be overestimated because the maskers are suffering from the non-mask group’s spreads.
4. This study design would not even proof that a 100% protection has a protective effect
Imagine a 100% perfect protection against COVID-19 (a hermetic room), what outcome should be expected for this by-definition safe group using this study design?
Here is the math only for estimating
- the false-positive antibody-tests
- positive test due to before-baseline infections
But as the study design grants protection at average only 4.5 hours/day infections outside the room should be added to the calculated expectations (in the study false-classified as noneffective protection).
The study reports antibody testing has an estimated 99,2% specificity. For about 2400 tests this leads to an expectation of 2400*0.008=19 false-positive tests in each antibody test group.
5. Participants in the experimental group when in close contact with other people, that do not contain air droplets by using facial masks, were exposed to similar risk of eye SARS-CoV-2 infection as the control group. Without widespread facial mask use in the community, the protective nature of facial masks (i.e. droplets containment) remains severely compromised in close encounters. Such performance bias pose serious constrains and challenges in effectiveness trial studies design and may induce error in result interpretation and decision making in health interventions.
Lisäksi on hieman huvittavaa, että tutkimuksessa tutkijat käyttivät tartunnan toteamiseen teidän parjaamaanne PCR-testiä, niin tässä yhteydessä se onkin ihan ok.
Tanskalainen tutkimus tehtiin reilu vuosi sitten n. 6000 tanskalaiselle. Alla hieman laajempi, yli vuoden tuoreempi, tutkimus, joka tehtiin 350000 ihmiselle Bangladeshissa. Tutkimuksen tulos: Surgical masks reduce COVID-19 spread, large-scale study shows.
https://med.stanford.edu/news/all-news/ ... id-19.html
Tuossa itse tutkimus:
https://www.poverty-action.org/sites/de ... 08.pdf.pdf
Aina sama kaava : Poimitaan joku lause tekstistä ja yritetään irrottaa se sisällöstä. Kun tämä menee vituiksi tulee kohta b eli hyökätään joko tutkimukseen väittäen "salaliitoksi" tai sitten mennään ihan vaan suoraan henkilökohtaisuuksiin.