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How confinement slows the chain of infection

2020-04-03T23:48:51.084Z


This measure aims to reduce the number of daily contacts of a person and thus lower the reproductive number of the disease. And it seems like he's getting it


Since March 14, with the announcement of the state of alarm, residents in Spain have been confined to our homes. The measure, which in principle will last until April 11, seeks to reduce the number of contacts we have on a daily basis. The objective is to be able to reduce the reproductive number of the virus, that is, the average number of people that each infected person can infect, and thus not collapse the health system. In short, flatten the curve that we have heard so much about.

One person has dozens of daily contacts. People you meet at home, at work, or on the subway. In the days that the disease lasts, that is hundreds of possible infections.

If a person is infected (although he may not have symptoms) and lives a normal life, all his contacts are at risk of being infected.

Covid-19 in Europe has a basic reproductive number (R0) close to 3. That number measures the transmission potential of the virus. In the absence of measures, each infected averages 3 people.

Each new patient infects 3 other people. The chain of contagion goes up to 12 patients in one more step.

If measures are not taken and this R0 of 3 infections per person is maintained, in three more steps we would have 120 infected and the contagion would continue exponentially.

The goal is to lower that reproductive rate. And for that, social distancing and confinement measures are taken. If those two people drop to a reproductive number of 2, 46 people are infected .

When R0 is close to 1, the outbreak stops growing exponentially. Each infected person infects another person alone and those infected tend to be constant, reducing to 6 infected. This prevents the healthcare system from collapsing.

The ideal scenario is to lower the R0 to 1. Then the outbreak tends to die out because there are fewer infected instead of more in each cycle.

Lowering that reproductive number is what the containment measures that we are suffering are pursuing: we want to limit contacts to stop the chain of infections.

This MIT study, led by the Spanish Esteban Moro, shows the effects that distancing measures have had in New York, such as the closing of schools or the order to stay home: the number of contacts outside the home has decreased from about 75 daily per person to just 5.

Average number of contacts

less than 25 meters

Close of

exercise

Not essensial

State

emergency

Purposes of

week

125

100

Close of

colleges

75

fifty

25

0

17

24

02

09

13

16

22

February

March

Source: Effect of social distancing measures in the New York City metropolitan area. MIT.

THE COUNTRY

Average number of contacts

less than 25 meters

Close of

exercise

Not essensial

State

emergency

Purposes of

week

125

100

Close of

colleges

75

fifty

25

0

17

24

02

09

13

16

22

February

March

Source: Effect of social distancing measures in the New York City metropolitan area. MIT.

THE COUNTRY

Average number of contacts

less than 25 meters

Close of

exercise

Not essensial

State

emergency

Close of

colleges

Purposes of

week

125

100

75

fifty

25

0

17

24

02

09

13

16

22

February

March

Source: Effect of social distancing measures in the New York City metropolitan area. MIT.

THE COUNTRY

In Spain we know, for example, that pedestrian traffic has evaporated in commercial areas across the country. In the center of Madrid, walks have been reduced to a tenth, as shown by the geolocation data of 300,000 mobiles.

This is how the Spanish have disappeared from the sidewalks

GPS data from some 300,000 mobiles shows how pedestrian traffic has evaporated in commercial areas across the country.

By Jordi Pérez Colomé and Daniele Grasso

These data say the measures will work. That is also the conclusion of the Imperial College report of March 30 (which has generated controversy for its estimate of the number of infected). The study estimated that the measures taken in Spain have lowered the reproductive number of the virus below 2 and perhaps 1.

Number

reproductive

virus (R0)

Distance

Social

Closing

from schools

Confinement

Interval

trusted:

6

95%

fifty%

4

two

0

10

17

24

two

9

16

2. 3

30

February

March

Number

reproductive

virus (R0)

Distance

Social

Closing

from schools

Confinement

Interval

trusted:

6

95%

fifty%

4

two

0

10

17

24

two

9

16

2. 3

30

February

March

Number

reproductive

virus (R0)

Distance

Social

Closing

from schools

Interval

trusted:

Confinement

6

95%

fifty%

4

two

0

10

17

24

two

9

16

2. 3

30

February

March

This slowdown is seen in the death toll. If we look at the cumulative deaths graph using a logarithmic scale, growth is not a straight line, which is what we see when the outbreak is in the exponential phase, but a curve whose slope flattens.

The curve in Spain is flattening out. That will not prevent deaths from continuing to grow in the coming days. Because the peak is perhaps yet to come and because even when it does it can be shaped like a plateau. But it is evidence that confinement, as in other countries, is capable of stopping the virus and surely suppressing it, at least temporarily.

Evolution of deaths

A logarithmic scale is used, which is better to observe the evolution of the epidemic. The distance between 10 and 100 is the same as between 100 and 1,000 ...

Change in the trend of the curve in Spain

Italy

Spain

USA

1,000 deaths

Start

outbreak

Korea

from the south

100

10

−5

0 days

5

10

fifteen

twenty

25

30

35

Source: self made.

THE COUNTRY

Evolution of deaths

A logarithmic scale is used, which is better to observe the evolution of the epidemic. The distance between 10 and 100 is the same as between 100 and 1,000 ...

There is a change in the trend of the curve in Spain

Italy

Spain

USA

1,000 deaths

Start

outbreak

Korea

from the south

100

10

−5

0 days

5

10

fifteen

twenty

25

30

35

Source: self made.

THE COUNTRY

Evolution of deaths

A logarithmic scale is used, which is better to observe the evolution of the epidemic. The distance between 10 and 100 is the same as between 100 and 1,000 ...

There is a change in the trend of the curve in Spain

Italy

Spain

USA

1,000 deaths

Start

outbreak

Korea

from the south

100

10

−5

0 days

5

10

fifteen

twenty

25

30

35

Source: self made.

THE COUNTRY

But ... what happens if we relax the measures?

On March 22, the Government asked Congress to extend the state of alarm for 15 more days, and on the 30th, it extended confinement to "non-essential" workers. A fear now is that when the isolation is relaxed the chain of contagions will be reactivated.

Experts suspect that isolating the sick will not suffice, because people around them - with or without symptoms - may be infected and continue the outbreak.

Comprehensive testing and contact tracing strategies have worked in South Korea. And technology can help. But the Imperial College report says, however, that other measures will surely be necessary, "or transmission will rebound rapidly, potentially producing an epidemic comparable in scale to that which would have occurred without intervention."

Although a patient isolates himself when he has symptoms, his relatives and other contacts may already be infected. If they live normal lives, they can infect other people before they get sick, and we risk the virus spreading again.

But if we maintain the habits of social distancing, we will lower that reproductive number of the virus and thus flatten the curve.

Although a patient isolates himself when he has symptoms, his relatives and other contacts may already be infected. If they live normal lives, they can infect other people before they get sick, and we risk the virus spreading again.

But if we maintain the habits of social distancing, we will lower that reproductive number of the virus and thus flatten the curve.

Although a patient isolates himself when he has symptoms, his relatives and other contacts may already be infected. If they live normal lives, they can infect other people before they get sick, and we risk the virus spreading again.

But if we maintain the habits of social distancing, we will lower that reproductive number of the virus and thus flatten the curve.

Although a patient isolates himself when he has symptoms, his relatives and other contacts may already be infected. If they live normal lives, they can infect other people before they get sick, and we risk the virus spreading again.

But if we maintain the habits of social distancing, we will lower that reproductive number of the virus and thus flatten the curve.

As long as there are not enough immune people (because they have passed the disease), returning to normal life is a risk. The virus could return to the first scenario of R = 3, so the growth in the number of infected would once again be exponential and we would saturate the health system again.

As long as there are not enough immune people (because they have passed the disease), returning to normal life is a risk. The virus could return to the first scenario of R = 3, so the growth in the number of infected would once again be exponential and we would saturate the health system again.

As long as there are not enough immune people (because they have passed the disease), returning to normal life is a risk. The virus could return to the first scenario of R = 3, so the growth in the number of infected would once again be exponential and we would saturate the health system again.

Otherwise, if we leave the measurements or lower them, we return to the first scenario of R0 = 3, so the growth in the number of infected would be exponential again and we would saturate the health system again.

Source: elparis

All life articles on 2020-04-03

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