(NewsNation Now) — Border Patrol’s approach to apprehending those coming into the United States illegally has changed dramatically during the coronavirus pandemic.

During the first year of the pandemic, over 90% of all migrants were expelled immediately, rather than processed into the immigration system, a stark difference from the pre-pandemic policy.

What caused the change is the presence of “CDC Title 42,” which essentially gives CBP permission to deport any migrant without giving them a chance to seek asylum.

The U.S. expelled migrants nearly 1.5 million times from March 2020 through November under Title 42 authority, named for a 1944 public health law that the Trump and Biden administrations have used to deny migrants a chance to seek asylum on grounds that it will curb the spread of the coronavirus. That accounts for about two of three arrests or expulsions at the border, most involving single adults and some families. Unaccompanied children have been exempt under President Joe Biden.

Unless you’re an unaccompanied child, you are generally given a health check and then sent back to your country of origin or Mexico.

Under the ban, people from Mexico, Guatemala, Honduras and El Salvador, are bounced back to Mexico before being afforded rights under U.S. and international law to seek asylum. People from other countries are flown home without a chance at asylum.

Pre-pandemic, migrants were taken into the U.S. and either held in CBP custody or released into the country while awaiting an asylum decision.

Since single adults cross the border more frequently than children, there are more expulsions than apprehensions.

This policy is also one reason CBP has seen a dramatic increase in the repeated crossing attempts by single adults. Last December, 23% of all individuals encountered were repeat crossers.

NewsNation reporters Robert Sherman and Katie Smith are spending three weeks traversing the southern border — starting in San Diego, California on Feb. 14 and ending in Brownsville, Texas later this month — telling the stories of communities in crisis. Follow our live blog here.