LOS ANGELES, Nov 16, 2022 (BSS:AFP) - A controversial US anti-immigration rule imposed at the height of the Covid-19 pandemic that automatically blocked asylum-seekers trying to enter the country has been struck down.

The measure, Title 42, had been branded "inhumane" by reformers and criticized as an ad-hoc immigration plan dressed up as a health policy.

Here's what you need to know about the rule:

- What is it? -

Title 42 is the colloquial name for a rarely used public health measure first invoked in 1893 when the United States sought to curb outbreaks of cholera and yellow fever.

In March 2020, the administration of then-president Donald Trump instituted the rule again as Covid-19 spread around the world.

Title 42 allows for the immediate removal of any foreigner or non-resident trying to enter the country without a visa.

There is no legal process, or any formal deportation to the country of origin, and a border agent can apply a Title 42 expulsion without the lengthy interview process usually required.

There were limited exceptions: thousands of Ukrainian nationals have been permitted to cross through the US-Mexico border and granted immediate entry because they were fleeing invading Russian forces.

- What happens at the border? -

The vast majority of people arriving at the southern US border have traveled from Central or Southern America.

There are usually two routes they take to try to enter the United States: an asylum claim, or an illegal crossing.

In pre-Title 42 times, if they made a claim for asylum, this kicked off a lengthy procedure that might see them processed in the United States or in Mexico.

But under Title 42, a border agent simply did not accept the claim and the applicant was refused entry. The process took a matter of minutes.

Anyone caught illegally crossing the border can be similarly and swiftly ejected. Significantly, this is done without the legal penalty normally imposed for an illegal crossing -- for example a ban on entering the United States, even to claim asylum, for a number of years.

This means that some migrants have tried repeatedly crossing, knowing they will not suffer legally if they do not succeed.

- What is wrong with swift removal? -

Activists say any system that prevents people from making an asylum claim is inhumane.

They point out that people presenting themselves at the US border are frequently fleeing brutal violence from gangs that rule swathes of Central and Southern America.

Conversely, the lack of legal penalty for an illegal crossing encourages people to take more risks to get over the border.

This can mean they are trying to make their way through hostile deserts or ford difficult rivers.

A total of 557 people died at the border in 2021, making it the deadliest year for migrants since records began in 1998.

- How many people has Title 42 affected? -

Because of the issue of multiple crossing attempts, it's impossible to say how many people have been refused entry under the rule.

What we do know is that there were more than 2.3 million migrant encounters at the southern border in the year to September 22. Many of those people were dealt with under Title 42.

- What's the public health argument for Title 42? -

The United States has the world's highest official death toll from Covid-19. It also has widespread infection among its population.

The benefits of preventing people from entering a country where the disease is well established are uncertain.

The US Centers for Disease Control and Prevention said in April it was in favor of ending the measure because of the relatively positive Covid situation in the country and the tools now available to fight the pandemic.

- What happened today? -

A federal judge struck down the policy, meaning asylum applications can once again be lodged at the border.

Hours later, the government filed a motion to have the decision suspended for five weeks, but stressed the measure was transitional to allow time for new controls to be put in place.

The five week stay means Title 42 will be gone at midnight on December 21.