As of today, people flyimg, or taking the train or even public
transit in Canada are advised to wear a face mask. Had a go
at making one from the US CDC instructions.
It is not uncomfortable, because one adjusts the width from the
inside. Just a tad suffocating 😒
* * *
source: Liberation, CheckNews
author: Florian Gouthière April 20, 2020 at 3:13 p.m.
translation: GoogleTranslate/doxa-louise
Covid-19: how is it that the rate of reproduction of the disease is decreasing?
Edouard Philippe announced at a press conference that the R-zero was now close to 0.6. That is, ten patients infect only six new people.
Hello,
Your question follows on from statements made by Prime Minister Edouard Philippe on Sunday during his press conference : “We mentioned this somewhat technical, but absolutely essential concept, which is called R 0 […]: the number of people that a patient infects; the transmission of the disease from one patient to how many other patients. If we do nothing, because this disease is fairly contagious, we observe a rate of the order of 3 to 4 […]. To reduce the epidemic, the R 0 […] must be equal to or less than 1. This is how we are able to reduce the circulation of the virus […] and to extinguish the epidemic gradually. Thanks to containment, epidemiologists believe that we have succeeded in getting this R0 [to a value close to] 0.6. In other words, ten patients only infect six new people. ”
The basic reproduction rate of a disease is a central concept in epidemiology. It makes it possible to characterize the epidemic potential of a disease. To estimate this rate precisely, many factors can be taken into account. However, in its simplest version, the calculation depends on three essential parameters.
First factor: the period during which the disease is contagious (usually expressed in days).
Second factor: the number of different people with whom we interact during a given period (generally expressed in “number of contacts per day”).
The last factor is that of the probability of transmission, in other words the ease with which contamination can occur during each “contact”. This variable can be influenced by different protective measures (hand washing, wearing a mask, etc.).
By multiplying the first two factors, we obtain the number of contacts potentially exposed during the contagious period. Multiplying by the last factor provides an estimate of the number of people that an infected individual is likely to infect. In other words: our rate of reproduction of the disease.
If one patient can infect more than one other, the disease spreads quickly. In the case of an R 0 of 2, an individual will contaminate two, each of thee will contaminate two others, who will themselves contaminate two others… 1, 2, 4, 8, 16, 32: not only does the disease spreads, but it spreads quickly.
When we speak of R 0 less than 1, this means that if we take a large number of infected people, we see that they have succeeded in infecting only a smaller number of individuals. If these new patients also contaminate an even smaller number of patients… the epidemic ends by itself.
Containment measures have a direct influence on the second factor mentioned above: the number of people with whom we interact during a given period. The decrease in our daily contact has, mathematically, resulted in a decrease in the number of people newly infected daily. The adoption of “barrier” measures, including more stringent hygiene measures, also affect the third factor in the equation.
The decrease in R 0 reflects a change in the dynamics of the epidemic. The infectious properties of the virus have not changed: if social interactions increase and “barrier” measures are less followed, the number of new daily cases starts to rise again.
The Prime Minister, during his press conference, set the objective that despite the deconfinement "the R 0 must remain equal to or less than 1" , explaining that the main lever for action was "prevention" , in other words our respect for barrier gestures.
When a part of the population is immunized against an infection (either by a previous exposure which generated an immune memory, or following a vaccination), the calculation of the reproduction rate of the disease is slightly modified . In fact, part of our social interactions is done with protected people, which mechanically reduces the spread of the pathogen. Epidemiologists speak of the "effective reproduction rate" of the disease. In the case of Covid-19, the number of months during which immunity remains acquired is unknown , and no vaccine has yet been found.
Florian Gouthière
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