PHOENIX (AP) — As the delta variant fuels an increase of COVID-19 cases in the U.S., some of President Joe Biden's critics blame the surge on his border policies, which allow some migrants to enter the country to apply for asylum.

Florida Gov. Ron DeSantis last week accused Biden of “helping to facilitate” the spread of the coronavirus. Fox News host Sean Hannity referred to migrants causing “the biggest super-spreader event” and incorrectly asserted that none was being tested.

But public health experts say arriving migrants are not driving the rising infections in the U.S. The main culprits are people who refuse to get vaccinated. Furthermore, migrants who are allowed to enter are generally tested for COVID-19 and given hotel rooms to quarantine if they test positive, though federal authorities have not made data available about such cases.

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WHAT HAPPENS WHEN MIGRANTS ARE STOPPED AT THE BORDER?

It varies, but most single adults are turned away, while unaccompanied children and some families are admitted to pursue asylum claims. This practice is in keeping with the Biden administration's continued use of Title 42, a public health rule adopted by the Trump administration at the start of the pandemic.

In June, the most recent month with available figures, Customs and Border Protection stopped single adults 117,602 times, resulting in 96,704 expulsions, or 82% of the total. Families were stopped 55,805 times at the border in June, with only 8,070 expulsions, or 15%. (Since some people attempt to cross more than once, these numbers refer to stops, not individual people).

Families who are allowed to enter the U.S. to apply for asylum are given dates to appear in immigration court or an appointment with immigration authorities. After they are dropped off in border communities, families typically travel to reunite with relatives, friends or supporters.

Children who arrive without parents are exempt from expulsion. They are typically held for less than a month at emergency shelters until they can be released to relatives or moved to licensed shelters.

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ARE MIGRANTS WHO ARE NOT EXPELLED TESTED FOR COVID-19?

Generally, yes. CBP, the agency that first takes migrants into custody, says they are given masks and referred to local health care providers for testing and treatment if they have symptoms.

From there, testing protocols can vary depending on which federal agency is involved. Most single adults and some families are transferred to Immigration and Customs Enforcement custody, where they all take COVID-19 tests.

All new arrivals are separated from the general population for 14 days and isolated if they test positive. Unaccompanied children are also tested before they are transferred to Health and Human Services Department facilities for minors, and then are given ongoing tests.

Some migrant families are released to border communities directly from CBP facilities, and this is where the government's information is less clear. The government says it works with local partners and “appropriate agencies” to test this population and quarantine those who are infected, but it has not clarified if that happens across the board. Often, local governments or nonprofits arrange testing and send those who test positive to isolate in hotels.

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HOW MANY MIGRANTS TEST POSITIVE FOR COVID-19?

The federal government has not disclosed this data, but in Texas’ Rio Grande Valley — the busiest stretch of the border for illegal crossing attempts — local officials recently publicized their own data.

On Aug. 4, local officials in McAllen, Texas, announced that out of nearly 88,000 migrants released by CBP in the city since mid-February, more than 7,000 had tested positive for COVID-19, which is a positivity rate of more than 8%. Catholic Charities of the Rio Grande Valley arranged hotel rooms for those infected. Positive tests became more frequent in recent weeks, surpassing 16% — a rate that county officials said was similar to the local population.

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WHAT DO PUBLIC HEALTH OFFICIALS SAY IS FUELING THE INCREASE IN CASES IN THE U.S.?

The key factors behind the recent spike in COVID-19 cases are people in U.S. communities who are unvaccinated and are not following guidance from Centers for Disease Control and Prevention about the highly contagious delta variant, according to public health experts.

At a news conference last week, Dr. Ivan Melendez, who serves as the local health authority in Hidalgo County, Texas, acknowledged that arriving migrants were “part of the problem” but he also said they did not pose any more of a danger than he does. "I have been in seven COVID units today.”

He said migrants are not responsible for introducing the virus nor do they have higher infection rates compared with the general population.

“Is it a pandemic of the migrants? No, it is a pandemic of the unvaccinated,” Melendez said.

The number of arriving migrants is far too small to be driving the enormous increases in cases across the U.S., said Dr. Joseph McCormick, a physician and former CDC epidemiologist now based at the Brownsville campus of the University of Texas Health Science Center at the Houston School of Public Health.

“Given what we are seeing now across the country, it just doesn’t work to try to attribute that to migrants,” McCormick said. Furthermore, experts say, the delta variant, which was first identified in India, began circulating in the U.S. before it was in Mexico or other parts of Latin America, where most migrants arrive from.

“So the claim that migrants entering from the southern border brought delta to the U.S. is baseless rhetoric,” said Max Hadler, senior policy director for Physicians for Human Rights, in a statement. “Rates are increasing everywhere, in every state in the country. It’s not a border issue or a migrant issue, it’s a national issue.”

As for people who evade the Border Patrol and enter the United States undetected, there is no reason to suspect that they would have higher rates of COVID-19 infection, McCormick said.

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HOW DO BORDER COMMUNITIES HANDLE MIGRANTS AS THE DELTA VARIANT SPREADS?

In many places along the border, local governments and nonprofits have a long history assisting migrants coming out of federal custody with food, clothing and travel arrangements. Local officials say the delta variant adds another challenge.

McAllen officials worked with Hidalgo County last week to erect a tent city to quarantine migrants who tested positive for COVID-19 and their family members. In other Texas cities, local leaders have expressed frustration with the governor's approach to the pandemic, which has included for blocking local governments from enacting mask mandates.

Brownsville, Texas, began a program to vaccinate arriving migrants about a month ago and has given shots to more than 860 migrants so far. Similar efforts are happening in other communities that receive migrants, including El Paso and Phoenix.

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DOES THE FEDERAL GOVERNMENT PLAN TO OFFER VACCINES TO MIGRANTS?

DHS denied recent media reports that federal officials are gearing up to offer vaccines to migrants after they are apprehended at the border. However, ICE has begun vaccinating immigrants held in detention. The government has also started inoculating unaccompanied children who are 12 and older with the Pfizer vaccine.