Travel restrictions - Printable Version

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Travel restrictions - BostonCard - 04-19-2020

I thought this visualization was useful to understand the effect of travel restrictions, and why most epidemiologists believe they are ineffective.  It is based on travel out of Wuhan to the rest of China, but the same models are used to evaluate travel between nations.



As you can see, even a pretty comprehensive travel restriction only buys you a few days and does nothing to reduce the magnitude of the peak of the outbreak.  That's because once an epidemic takes hold in an area, growth from community spread is much larger than growth of imported cases.  I view it a bit like a forest fire giving off burning embers which could light a nearby house.  If you cut down on the number of embers that are given off that might delay when the house catches fire, but if there is already a small fire in the house, preventing more embers from hitting the house is going to be of limited benefit unless you can put out the fire that is already in the house.

That's illustrated by the figure below:



A travel ban can only work if it is implemented in conjunction with other measures to reduce the community spread of infection.  The travel time might buy you some time, but it won't prevent an outbreak.  Social distancing can keep a lid on community spread.

The administration implemented a travel ban and declared victory.  A little bit like George W. Bush's "Mission Accomplished" victory lap.

Figures from the awesome medium medium post by Tomas Pueyo: https://medium.com/@tomaspueyo/coronavirus-act-today-or-people-will-die-f4d3d9cd99ca

BC

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RE: Travel restrictions - M T - 04-19-2020

Pretty pictures, but no explanation behind them in the article linked to.

It isn't clear to me why a travel ban can't help, when you don't have but a handful of cases already, or when you are trying to contain the disease within a hot spot.    Such a ban is like wearing a mask.  Whether you're trying to keep the virus in or out, it reduces the ones that get through, and maybe you can take care of them.

Certainly it would make a difference whether 1 infected person gets through a travel ban, or 500 get through with no travel ban.  Obviously, a travel ban isn't a panacea, but it is a start.

I don't mean to knock the WHO as I know they are helpful, but the push for no ban on travel was from the same WHO that said masks were not recommended (says the guy who was wearing a mask in the 3rd week of February when at a concert & when flying).

Pretty pictures, but no useful information.   I get that someone is trying to make a point, but the picture doesn't convey any information, it just is making its position known.

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RE: Travel restrictions - BostonCard - 04-19-2020

From the blog:

Quote:This chart shows the impact that the Wuhan travel ban had delaying the epidemic. The bubble sizes show the number of daily cases. The top line shows the cases if nothing is done. The two other lines show the impact if 40% and 90% of travel is eliminated. This is a model created by epidemiologists, because we can’t know for sure.
If you don’t see much difference, you’re right. It’s very hard to see any change in the development of the epidemic.
Researchers estimate that, all in all, the Wuhan travel ban only delayed the spread in China by 3–5 days.

A travel ban doesn't do much because once there is community transmission, local transmission increases exponentially.  The only way a travel ban is helpful is if it is so airtight that no new cases come in.  Otherwise, the travel ban (on its own) does nothing.  It's a little like the Chinese shutting the Wuhan seafood market (if that is how the animal to human transmission happened) after there was already human to human transmission.  Or, as they say, it's like closing the barn door after the horses have left.

Could a travel ban be useful?  If you can reduce local transmission to the point where the virus can be contained, then having a travel ban can prevent the reintroduction of disease from places where it is out of control, especially if you can't track and trace visitors easily.  But on their own, and in the setting of local transmission, a travel ban is like pissing in the ocean.  And worse, it distracts you from focusing on other things.

BC

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RE: Travel restrictions - Genuine Realist - 04-19-2020

(04-19-2020, 04:36 PM)BostonCard Wrote:  From the blog:

Quote:This chart shows the impact that the Wuhan travel ban had delaying the epidemic. The bubble sizes show the number of daily cases. The top line shows the cases if nothing is done. The two other lines show the impact if 40% and 90% of travel is eliminated. This is a model created by epidemiologists, because we can’t know for sure.
If you don’t see much difference, you’re right. It’s very hard to see any change in the development of the epidemic.
Researchers estimate that, all in all, the Wuhan travel ban only delayed the spread in China by 3–5 days.

A travel ban doesn't do much because once there is community transmission, local transmission increases exponentially.  The only way a travel ban is helpful is if it is so airtight that no new cases come in.  Otherwise, the travel ban (on its own) does nothing.  It's a little like the Chinese shutting the Wuhan seafood market (if that is how the animal to human transmission happened) after there was already human to human transmission.  Or, as they say, it's like closing the barn door after the horses have left.

Could a travel ban be useful?  If you can reduce local transmission to the point where the virus can be contained, then having a travel ban can prevent the reintroduction of disease from places where it is out of control, especially if you can't track and trace visitors easily.  But on their own, and in the setting of local transmission, a travel ban is like pissing in the ocean.  And worse, it distracts you from focusing on other things.

BC

I forget the category of human being who rushes in where angels fear to tread. But I will join that number by suggesting that the timing of a ravel ban is more important by quantum degrees than with other forms of social distancing. A restriction to a small geographical area must limit the spread of the virus. Surely, if the ban is imposed ASAP after the virus is identified, there is some reasonable chance to achieve that result.

What is not in dispute is that the travel ban on January 31st was too little, too late, and not effective at all.

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RE: Travel restrictions - OutsiderFan - 04-20-2020

Good stuff. New Zealand’s travel ban worked well because they shut down all inbound flights from anywhere. I believe they had mandatory quarantines for all visitors even before that as well.

I’m still concerned about domestic air travel. Anyone else get the email from the AA CEO last week? He was claiming AA had “increased social distancing” on their planes, conveniently forgetting everyone breathes the same air when on them. I think the reality is the market has given airlines social distance to a much larger degree than the airlines themselves.

Give me a self-contained breathing apparatus, and I’m totally ready to fly somewhere.

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