Washington — The acting head of the Federal Emergency Agency (FEMA) told lawmakers on Tuesday that less than 6% of COVID-19 tests for migrants at the U.S.-Mexico border have come back positive, a lower percentage than the overall positivity rate in the state of Texas.

“There’s testing happening,” Acting Administrator Robert Fenton told lawmakers at a hearing before the House Appropriations Subcommittee on Homeland Security. “What we’re seeing is less than 6% positive right now, coming across the border.”

Fenton’s comments come as Texas Governor Greg Abbott and GOP lawmakers have expressed concerns that migrants are spreading the virus to the general public. However, the rate of infection among migrants tested at the border is lower than that of the state overall. As of Tuesday, the seven-day average of the state’s positivity rate stood at 7.4%, according to Johns Hopkins University.

FEMA’s reported positivity rate among migrants squares with an assessment by Trey Mendez, the mayor of Brownsville, Texas. Mendez told CBS News earlier this month that 108 out of roughly 1,800 migrants who were brought to Brownsville tested positive for COVID-19, a positivity rate of 6.3%.

Migrants who were previously processed under the Trump administration’s Migrant Protection Protocols (MPP) program are now tested by border officials before entering the U.S., as the federal government works to process as many as 25,000 eligible individuals who were previously required to wait in Mexico for their immigration court hearings.

While the Biden administration has abandoned the Trump-era pandemic-related policy of summarily expelling unaccompanied children, it has continued to use the public health authority to expel most single adults and some families with children from the southern border.

Since the end of January, the Texas Division of Emergency Management has sent 40,000 rapid COVID-19 tests provided by the federal government to border communities, including Brownsville, McAllen, Laredo and Del Rio. The acting FEMA chief told lawmakers that “anyone that is at risk can be tested by local or state government and FEMA reimburses those costs 100%,” and said the federal government is also supporting testing programs in California and Arizona.

Last week, Abbott lifted Texas’ statewide mask mandate and allowed most businesses to operate at 100% capacity. The relaxing of restrictions comes as a rising number of immigrants are overwhelming federal detention facilities along the border and the Biden administration scrambles to provide adequate shelter to unaccompanied minors crossing into the U.S.

The surge in unaccompanied migrant children has led to overcrowding at Customs and Border Protection facilities that are built to hold adult migrants. In February, nearly 9,500 unaccompanied minors, many from Central America, were taken into U.S. border custody, marking a 21-month high. Unaccompanied children must legally be transferred to the custody of the Department of Health and Human Services (HHS) within 72 hours, but a lack of bed space has led to a massive backlog of cases.

“The Border Patrol facilities have become crowded with children and the 72-hour timeframe for the transfer of children from the Border Patrol to HHS is not always met,” Homeland Security Secretary Alejandro Mayorkas conceded in a statement issued Tuesday morning. “HHS has not had the capacity to intake the number of unaccompanied children we have been encountering.”

The secretary also confirmed that HHS holds unaccompanied children for testing and potential quarantine before they can be placed with a sponsor based in the U.S.

For months, the Office of Refugee Resettlement, the agency within HHS responsible for housing unaccompanied children, has required newly arrived children to test negative for the coronavirus twice before being released, or undergo quarantine if they test positive. As of February 25, no unaccompanied minor has required hospitalization for COVID-19, according to the refugee office.

Dr. Marcella Nunez-Smith, chair of the White House’s COVID-19 Health Equity Task Force, said Sunday she had not seen evidence indicating that undocumented immigrants crossing the border into Texas are spreading the coronavirus.

“I have not seen any evidence to support that at all,” she said in an interview with “Face the Nation.” “I think that it’s very important for us, you know, again, as we talk about our goal to vaccinate an entire nation, that we not divide ourselves in this process.”

On Saturday, Mayorkas announced that he directed FEMA to help process and care for unaccompanied migrant children entering Border Patrol custody.

A FEMA spokesperson told CBS News the agency is working with HHS to “quickly expand capacity for safe and appropriate shelter, and to provide food, water and basic medical care.”

The emerging crisis at the border comes as the Biden administration works to encourage minority and marginalized communities to receive their COVID-19 vaccinations, regardless of immigration status.

“We’re very mindful of the fact that people need to access medical attention in the fight against this pandemic irrespective of their immigration status in the United States,” Mayorkas told CBS News earlier this month. “And we are executing on that overarching public health order.”

Camilo Montoya-Galvez and Melissa Quinn contributed to this report.