Scientific reason to reduce quarantine to 7 days?

[CanadaSam]

Almost all scientific studies around the world show that the mean (average) incubation period for covid is about 5.5 days.

 

As I understand it, across all age groups, this is the period (day 5.5 after exposure) which has the highest probability of your showing symptoms, and probably this would be the time when, if you get tested, would have the highest probability of your definitively showing if you have the virus, or not.

 

A PCR test carried out on day 6 of quarantine would catch the vast majority of infected people, keeping people after day 7, in my opinion is being overly cautious, to the detriment of the tourism industry and economy of Thailand.

 

Your thoughts?

 

One study, please read the middle of the "Results" section:

https://www.nejm.org/doi/full/10.1056/NEJMoa2001316

Another:

https://bmjopen.bmj.com/content/bmjopen/10/8/e039652.full.pdf

Edited October 30, 2020 by CanadaSam
Added Links.

[Frank67]

Actually I was expecting that quarantine was reduced to 7 days quickly with the knowledge which was built over the corona virus in the first months and after a successful trial period could even been reduced down to 5 days.

Why?

I do not see scientific evidence for a 14 day quarantine as long as you believe in the quality of PCR tests. If you got infected before or during the flight, within the 5 days the virus should be detacable. If it isn't this will most probably also not change in the following days nor will you develop any symptoms. The new antigen tests should even increase the detection accuracy in combination with PCR tests.

Certainly, if you do not trust your test labs at all, then you have to wait 14 days to check for symptoms. But why should labs in Thailand be so bad to fail in multiple tests on the same person??

 

I see the risk that someone with a infection slips through a 7 days quarantine, but would be detected in a 14 day quarantine much higher than catching an infection from new arrivals in the same hotel during quarantine.

 

So a very strict 7 or even 5 day quarantine  should be preferred over a 14 day quarantine.

This could even be improved by a rhythm which allows arrivals to a hotel only every 7 days.  It requires quarantine hotels working in a round robin scheme.

 

So why is it still 14 days?  Political motivation?

[rabas]

One scientific issue is that even experts don't have exact answers. Measured incubation curves many not be exact for on all races, ages, health conditions, etc. They are estimates. The Cambridge curve says:

 

"Of symptomatic cases 95% showed symptoms by 13.7 days and 99% showed symptoms by 17.8 days."

 

Another problem is when will a PCR test show positive? Even after 3 days of symptoms 20% of PCR tests are still negative, link. Then there are asymptomatic cases that are infectious.

 

If your goal is to prevent a nation form being reinfected (like Thailand) how many CASES can you let slip in?

[Frank67]

As far as I understand there is a huge difference between symptoms and the amount of virus to be found in your throat. Virus is there in masses a few days before symptoms are recognized and are already infection.

The time from infection to becoming infectious is estimated to be just between 2.5 and 4 days (source). So an infected person being infective should be detectable at this point of time by PCR or antibody tests . From then on the number of viruses is going down continuously.

 

A from this general finding independent interesting information would be how many days after arrival guests in quarantine have been detected positive in Thailand. There has been a significant number which should be enough to extract meaningful statistics.

 

As the chance that someone with the virus passes the quarantine is never absolute zero it is all about statistics to eliminate this risk to a certain acceptable average minimum.

 

Thailand is not much different from other countries including my home country. A lot of numbers are published but never complete and rarely in the right context, corelation and with detailed sources. The economic damage as well as the death toll - depending on the related governments preference - caused by estimations and blur is one result. I am actually disappointed that there is no better information available world wide.

 

Many countries kept the 14 days quarantine duration as a benchmark from the early phase of this pandemic  which was based on the detection of obvious symptoms and worst case observation. In the meantime - after more than half a year - we should have basis to find the right duration. Don't get me wrong. It might even lead to the same duration of 14 days, but for different reason and the reason should be transparent to people.

 

[Frank67]

Looks as if the duration of quarantine is about to be reduced: https://www.nationthailand.com/news/30396551

As the estimated ratio of infected slipping through a 10 days quarantine is 0.00015%. https://www.nationthailand.com/news/30397415

 

 

[rabang]

It is still 7 days too much for 99,99% of tourists.

[Sheryl]

A mean is not the point at which the majority will be positive.

 

It is just the average value.

 

Even the median - -which people often (wrongly) confuse with the mean - is only the point reached by  50%, i.e. it is the point at which an equal number of people fall above or below.

 

You definitely do not set quarantine recommendations based on means or medians.  Rather you look at the interval which 95 - 99% of cases will fall into

 

95% will be positive by day 10

 

99% by day 14

 

I don't off hand know for day 7 but with the mean being 5.7 and a fairly wide standard deviation, it is sure to be pretty low. Maybe 60%, give or take.

 

No public health authority would suggest a quarantine period of only 7 days, makes no sense.

 

10 days is really minimum and it will miss 5% of cases. Now if it is applied to peopel coming from low risk areas, that doesn't transfer into much. But if applied to people from higher risk areas, it could.

[Frank67]

What is a hight Risk area? Where I am right now, we have 0.25% of the population with known infection. The very very most of them would not travel due to this fact. OK, there is a quantity of additional people who do not know that they are infected.  They

 

The second source I mentioned came to the conclusion that days 11-14 in total alow to identify additional 1.1 persons in a million (1.5 - 0.3) which is far away from 4% - 363 times less.

I even think that the chance a person is infected during the last 4 days in quarantine is much higher that 1.1 in a million and that this case has not been taken into account doing the probability calculation. The ideal case of totally isolated tourists during quarantine is a wrong assumption.

It would be interesting to know the percentage of the total identified infections during quarantine.

 

Was it in 2018 almost 40 million tourists coming to Thailand? Even in an extremely utopian and uncertain assumption that with a 10 days quarantine the same number of tourists could be reached it meant that a total of additional 44 people would enter the country carrying the virus in a total year.

My personal assumption is that the number of people crossing borders illegally with an infection is much higher but seams o be controllable. In contrast to illegal immigration the tourists can be tracked pretty well.

 

Away from numbers to emotional human beings: I personally would accept a 3 day quarantine, maybe a 5 days I would still consider to do. 14 days - practically it is 16 days - will defend pretty well from tourists coming to Thailand in relevant numbers.

 

What does it mean to Thai people: 15% of the GPD was in international tourism and is lost. Many many people lost job, their business, lifetime investments, family income and chance to pay for healthcare. So the toll for them is pretty high and must be balanced with the risk caused by tourists bringing the virus with them.