The rapper Tekashi69 walked out of a federal prison on Thursday, four months short of his two-year term, thanks to a nationwide effort to stem coronavirus outbreak risks at jails and prisons, which health advocates fear might become a tinder box for infections.

Tekashi69 (born Daniel Hernandez), 23, will finish the remainder of his sentence in home confinement, his lawyer, Lance Lazzaro, said.

Last year, Mr. Hernandez — also known as 6ix9ine — pleaded guilty to a series of gang robberies and shootings, cooperating with authorities by testifying against his former associates in the gang Nine Trey Gangsta Bloods. He has asthma, which his lawyer argued gave him a heightened vulnerability to the coronavirus.

U.S. District Judge Paul A. Engelmayer, who sentenced him, agreed, saying that the pandemic presented “extraordinary and compelling reasons” for a compassionate release of Mr. Hernandez, who, he wrote in his order on Thursday, “no longer will present a meaningful danger to the community if at liberty.”

Last week, Judge Engelmayer wrote in a guidance to the Bureau of Prisons: “Had the Court known that sentencing Mr. Hernandez to serve the final four months of his term in a federal prison would have exposed him to a heightened health risk, the Court would have directed that these four months be served instead in home confinement.”

The coronavirus pandemic has created mounting, and sometimes conflicting, pressures on prison and public health officials as they scramble to avert a crisis inside and around prison walls. Discharging criminals is typically unpopular with law enforcement and sometimes criticized by victims’ rights groups, and it also raises questions about who qualifies for mercy. Some cities and states have taken broad actions to release swaths of nonviolent offenders in an effort to mitigate the spread behind bars. But the fate of other inmates is decided individually, with petitions to judges.

Mr. Hernandez’s underlying health issues, his earlier cooperation with the authorities and the short remainder of his sentence may have made him a good candidate for release. But other high-profile inmates, like Bill Cosby and R. Kelly, are arguing for home confinement too, so far without success.

“You have to make some actuarial decisions based on who presents the least public safety threat,” said Michael Jacobson, director of the CUNY Institute for State and Local Governance and former New York City correction commissioner. “It’s all going to present some level of risk, but we already know the level of risk if you don’t do it.”

Mr. Lazzaro, Mr. Hernandez’s lawyer, said that the rapper was treated for shortness of breath in the last week, but was feeling better now.

A rising music star and internet personality once known for his long rainbow-colored locks, Mr. Hernandez, who grew up in Brooklyn, had a multiplatinum hit song, “Fefe,” with Nicki Minaj in 2018, and signed a $10 million record contract shortly before he was sentenced last December. His persona was built around boasts that he could outrun the law even as he live streamed videos of himself with guns and taunted rival gangs online. But after he was arrested on firearms and racketeering charges in November 2018, Mr. Hernandez began speaking with the government and agreed to testify for the prosecution against his former gang mates.

Mr. Hernandez, prosecutors noted, turned against Nine Trey Gangsta Bloods — a faction of the Bloods — at great personal risk. As a result, he was held in a private prison that was run by U.S. Marshals, his lawyer said, and the location of his home confinement could not be revealed. The paperwork that related to his release was not filed publicly until he was in his new residence, to “ensure the safety of law enforcement agents and Mr. Hernandez upon his release from custody,” according to a letter from the Justice Dept. to the courts.

Mr. Hernandez had previously rejected the idea of entering the witness protection program, saying he planned to continue making music upon his release, which is set for July 31 (he was given credit for time served at his sentencing).

“He has no intention of going into” witness protection, Mr. Lazzaro said on Thursday. “He hopes to resume his career.”

The rapper’s release comes as prison reform advocates and some health officials are sounding an alarm about a potential disaster among the incarcerated, citing the impossibility of social distancing in prison cells, the banning of hand sanitizer, and the likelihood that corrections officers would spread the illness in their communities, as the virus catches on. Thousands of inmates and officers in municipal, state and federal facilities have already tested positive, and at least five inmates at federal facilities have died because of the coronavirus outbreak since March 28, according to the Bureau of Prisons.

Since Attorney General William P. Barr wrote a letter on March 26, directing federal institutions to prioritize home confinement, the Bureau of Prisons has placed 471 inmates into residences, a spokesman said.

Though several prominent individuals have asked for clemency in recent weeks, few have succeeded. Agustin Huneeus Jr., 54, a winemaker sentenced to five months in federal prison for his involvement in the college admissions scandal, was released in March, two weeks early, because of “unique health circumstances.”

R. Kelly, who is being held on federal charges in Chicago, also recently filed a petition for his release, citing a higher health risk tied to a recent surgery. “I think his fame works against him,” Steve Greenberg, Mr. Kelly’s lawyer, said on Thursday. “If she lets him out, it will be, ‘He got special treatment because he’s R. Kelly,’” he said, referring to U.S. District Judge Ann M. Donnelly, who is overseeing the case. “And if she doesn’t let him out, people will say she didn’t let him out because he’s R. Kelly.”

Bill Cosby’s lawyers are working on his petition, said Andrew Wyatt, a representative for Mr. Cosby, but are holding off to see if Pennsylvania lawmakers will first vote to release inmates facing a high risk of contracting the coronavirus. Mr. Cosby is 82 and blind, Mr. Wyatt said, and two inmates in the same facility have tested positive for the virus.

“He has 18 months left before he can go before the parole board,” Mr. Wyatt said on Thursday. “Are you saying you’re not going to give him a fighting chance? He was not given a life-or-death sentence.”

The greatest challenge judges have to face, Mr. Jacobson said, is figuring out the bar for who can go home and who can stay — and doing so quickly, before the virus continues to spread.

“None of this is easy,” Mr. Jacobson said. “But what choice do we have?”