Thousands of migrants head north from central America, through Mexico, every year seeking a better life in the US.
The pandemic has meant this flow of migrants may create a national health risk as few if any arrive with recent negative COVID-19 tests.

The US Ambassador to Guatemala, William Popp, said at the weekend any migrants who cross the US border "in an irregular manner" will be sent back to their home country.
Mr Popp met Guatemalan Foreign Minister Pedro Brolo and the Mexican Ambassador to Guatemala Romeo Ruiz.
Afterwards Mr Brolo said: "Any attempt to create massive flows of people will not be tolerated and will be countered."
Mr Ruiz told Guatemalans: "Please don't leave your homes, don't put your families in danger, don't put your children at risk."
But their tough talk contrasts with the noises emerging from the White House.
#UPDATE Guatemalan police fired tear gas on Sunday to disperse thousands of migrants headed for the United States on foot, and soldiers beat back a group that tried to push through barriers, AFP journalists witnessed https://t.co/V9AbAPajtN #VadoHondo
— AFP News Agency (@AFP) January 17, 2021
📷 @johanordonez pic.twitter.com/69cX4xSUBt
Last week, on the day of his inauguration, Biden cancelled the “emergency” Trump had declared along the Mexican frontier and said “building a massive wall that spans the entire southern border is not a serious policy solution.”
Biden said: “My administration is committed to ensuring that the United States has a comprehensive and humane immigration system that operates consistently with our nation’s values.”
But the danger is that by softening America’s stance on migration - for example scrapping the policy of detaining child migrants travelling alone - Biden could encourage more migrants.
Biden's immigration reform bill will:
— American Immigration Council (@immcouncil) January 21, 2021
1. Create a pathway to citizenship.
2. Reform the immigration court system.
3. Modernize border security.
4. Address root causes of undocumented migration.https://t.co/pR3ZQXPwAN
Biden, in his statement, said he intended to pause work on construction of the wall and would being an “assessment of the legality of the funding and contracting methods used to construct the wall.”
The Trump administration committed US$15 billion towards building a wall along the entire 800 mile frontier with Mexico.
He promised Mexico would pay for it - they have not paid a cent.
Where Trump had signed legally binding contracts with construction companies it may be virtually impossible for Biden to cancel them without incurring huge penalties for breach of contract.
The Biden administration is promising more “carrot” and less “stick” - more investment in the three central American which generate the most migrants.
Mexican President Andres Manuel Lopez Obrador - better known as AMLO - spoke to Biden on Friday, 22 January, about the root causes of the migration crisis.
Mexico has promised to try and stop caravans of migrants heading north from the Guatemalan border and welcomed Biden’s decision to reverse the previous administration's “draconian immigration policies.”
In the last 20 years the Mexican economy has massively improved and fewer Mexicans seek to migrate to the US.

Nowadays most of those flooding across into California, Arizona, New Mexico or Texas are Hondurans, Guatemalans or Salvadoreans.
They often are fleeing violence as well as poverty but sometimes they bring with them allegiances to murderous gangs such as MS-13 or their rivals, Barrio 18.
Earlier this month 4,000 corralled in the Guatemalan town of Vada Hondo and prepared to head north into Mexico.
President Alejandro Giammattei ordered troops to break up the caravan after learning none of the migrants had travel documents or proof of negative coronavirus tests.
Guatemala has accused Honduras of doing nothing to prevent its citizens giving up on their country and heading north.
AMLO said at the weekend Joe Biden has told him his new administration would send US$4 billion to help economic development in Honduras, El Salvador and Guatemala.
It remains to be seen whether that will be enough to stem the tide.