America’s prisons, jails and detention centers have been among the nation’s most dangerous places when it comes to infections from the coronavirus. Each day over the past year, more than 1,400 new inmate infections and seven deaths, on average, have been reported inside those facilities.

The cramped, often unsanitary settings of correctional institutions have been ideal for incubating and transmitting disease. Social distancing is not an option. Testing was not a priority inside prisons early in the pandemic. With little public pressure, political leaders have been slow to confront the spread.

The virus shot through many institutions, leaving the incarcerated desperate for ways to avoid getting sick. At Pickaway Correctional Institution in Ohio, which housed about 1,900 people, they tried to turn bedsheets into tents to separate themselves; 4 in 5 inmates were infected anyway.

At an immigration detention center in Farmville, Virginia, nearly every detainee — 339 in all — was infected. And at the Fresno County Jail in California, where most people are held on charges for which they have not yet been convicted, more than 3,800 were sickened.

Starting in March of last year, New York Times reporters tracked every known coronavirus case in every correctional setting in the United States, including state and federal prisons, immigrant detention centers, juvenile detention facilities, and county and regional jails.

The Times measured the pandemic’s excruciating impact on prisoners using records requests and interviews with people from all corners of the system and spoke with incarcerated people and their families, prison wardens, jailers, prosecutors, defense attorneys and civil rights groups.

A year later, 1 in 3 people incarcerated in state prisons are known to have had the virus, the data show. In federal facilities, at least 39% of prisoners are known to have been infected. The true count is most likely higher because of a dearth of testing, but the findings align with reports from The Marshall Project and The Associated Press, UCLA Law and The COVID Prison Project that track COVID-19 in prisons.

The virus has killed prisoners at higher rates than the general population, the data show, and at least 2,700 have died in custody, where access to quality health care is poor.

A month after a parole board approved the commutation request on his life sentence, Bruce Norris, 69, was still in custody, awaiting the Pennsylvania governor’s signature, when he died from the coronavirus. In a crowded Texas federal prison, Andrea Circle Bear, 30, was serving a two-year drug sentence. She died from the virus shortly after giving birth while on a ventilator.

Alan Hurwitz, 79, had lung and throat cancer. He was denied compassionate release several times from the North Carolina federal prison where he was serving for a series of bank robberies. When he was finally freed, he fell ill on the flight home. A medical examiner determined that he died from the coronavirus.

These deaths and many of the more than 525,000 infections so far among the incarcerated could have been prevented, public health and criminal justice experts say.

Prisons and jails are sometimes so crowded that three people sleep in cells designed for one person. Prisons have not adequately quarantined sick inmates and have often not required testing for correctional officers. Prisoners have also been given low priority to receive vaccinations, even as cases have continued to rise.

A year into the pandemic, prison officials around the country have acknowledged that their early approach was muddled and based on trial and error. The novelty of the virus, some said, made early decisive action nearly impossible because so little was known about how it spread. In some states, the disorganized response lasted well into the pandemic.

In addition to inmates, more than 138,000 prison and jail correctional officers were sickened, and 261 died, according to the Times data.

Despite warnings, many prisons were unprepared to handle the virus.

Alvin Murray, 71, was relieved when he learned last February that he would be transferred to the Duncan prison, a state facility for older inmates about 100 miles north of Houston. The salt and pepper in the chow hall was a sign that conditions were better there than in his previous prisons. At one facility, Murray, who was convicted of arson and property theft and was serving a 20-year sentence, had nearly died of pneumonia, his relatives said.

By then, public health officials were warning wardens that prisons needed to take precautionary measures against the virus, especially for older prisoners. Health officials said that without basic steps, including social distancing, better sanitation and less crowding, correctional institutions had the potential to become incubators for the virus.

Few states heeded these early warnings, and many focused their efforts on keeping the virus out of prisons — including prohibiting family visitations — rather than preparing to handle outbreaks once the virus got inside. One Texas prison failed to supply sufficient soap, left sinks in disrepair and banned hand sanitizer, a court found.

In other states, prisons continued transferring people from one facility to another, often failing to test them first. Others did not enforce rules requiring guards to wear masks.

But prisoners and civil rights groups say the most significant impediment to containing the virus has been the crowding that has become prevalent in U.S. prisons. Since the 1980s, the nation’s prison population has increased by more than 500%.

States have so many inmates that gyms have been converted into housing areas, recreational yards have been shrunk or eliminated to accommodate more beds, and prisons have shifted from cells to dormitory-style housing, with people sleeping in double- or triple-tiered bunks that fill nearly every bit of floor space.

The changes have meant that when the virus entered a prison, it spread quickly. At Duncan, it hopped from bed to bed last summer, infecting three-quarters of inmates.

Jeremy Desel, a spokesperson for the Texas prison system, said authorities did everything possible to keep the virus at Duncan under control, including intensive cleaning of the facility, extra soap and extensive testing. He said those actions saved lives.

But in the end, 279 prisoners and 66 staff members were infected, and Murray, 20 other inmates and one staff member died.

Prisons did not move quickly enough to test employees or provide contact tracing.

Prisons and jails have only sporadically traced the contacts of infected prisoners and guards to understand who was at risk of exposure. This has inhibited their ability to prevent the virus from entering facilities and to limit its transmission, public health officials said.

Early in the pandemic, one of the hardest-hit places was the Oakdale federal prison, with about 1,900 people in rural south Louisiana. An outbreak there infected 689 inmates and guards, and nine inmates died.

At Oakdale, an investigation by the Justice Department’s Office of the Inspector General found that a series of mistakes by prison officials and rules violations by staff members had allowed the virus to proliferate.

The report found the virus appeared to have been introduced by a Bureau of Prisons teacher who visited New York City in March 2020. There was no evidence that the prison had screened the teacher or tested him before he resumed teaching prisoners. (The Bureau of Prisons declined to comment about the Oakdale outbreak.)

On March 11, the day after the teacher resumed instruction, he reported feeling ill. Still, he kept teaching, and students who were housed in different parts of the sprawling facility mingled in his classroom.

Eight days later, inmates started complaining of symptoms. The prison did not screen them consistently for the virus, and staff members did not wear masks or other protective gear while transporting and guarding sick inmates at hospitals.

It was not until March 26 that protective gear was distributed. By then, hundreds were believed to have been infected, though the precise number is not known because the prison did not start testing inmates until mid-April.

A later round of contact tracing identified the prison’s Education Department as the common nexus; the first four inmates to test positive shared a class, and the first inmate to die was an assistant to the teacher who had fallen ill.

Few governors granted widespread releases of prisoners, leaving the most vulnerable in custody.

For months, Clarence Givens, 70, stayed in his 6-by-8-foot cell at Stanley Correctional Institution in Wisconsin, isolating with his cellmate. He had asthma, relied on a breathing machine for obstructive sleep apnea and was frightened of getting sick.

Givens, in prison for heroin possession, said that he was hoping to be released early, though he had not filled out paperwork seeking compassionate release. He died from COVID, authorities said, in December.

Only a handful of states have released more than a few thousand people early, despite calls from a variety of groups and some prosecutors to reduce prison populations amid the pandemic.

Ultimately, 421 inmates and 135 correctional officers at Stanley were infected, and three inmates did not survive.

Once Givens fell ill in November, other inmates said they aided him as best they could. He continued to stay in his cell.

“He wasn’t eating too much for days, but I did force him to drink our juices they gave us, to eat some fruits, water and I finally got him to eat some soup and some cereal, the whole pod donated vitamins, some Emergen-C vitamin C, teas, vitamin D, and other vitamins from canteen and I just kept having him take them and drink plenty of fluid,” a prisoner wrote to Givens’ wife. “I had to assist him in it all cause he couldn’t barely sit up or even dress.”

John Beard, a prison system spokesperson, cited health care privacy laws in declining to answer questions about Givens.

Slow vaccinations and the threat of variants leave an uncertain landscape.

Prisons’ pandemic response has improved by some measures in the past year; testing, especially at intake, and mask-wearing are more widespread. But prisons were built with security in mind and not to act as hospitals or hospices. Given the age and poor health of many incarcerated people, they remain especially vulnerable to infection and illness.

In recent weeks, more contagious variants of the virus have appeared in prisons in Colorado, Michigan and elsewhere. Public health officials say the presence of variants in prisons is likely to be more widespread than known because most facilities do not regularly screen for them.

Early in the nation’s vaccination program, incarcerated people in most states were not given priority to be inoculated, though they have an elevated risk of infection and death. By April, most states had announced plans to vaccinate prisoners in subsequent months.

Still, many inmates and correctional officers have been reluctant to get the shots, according to state prison systems and jails. All of it has left the likelihood of eliminating future outbreaks uncertain, public health experts say, even after much of the nation is vaccinated.

“It’s inevitable once that new strain gets here, it’s going to spread like wildfire,” James Moore, a prisoner at G. Robert Cotton Correctional Facility in Michigan, said in an interview last month. “It’s inevitable. So we’re basically just sitting back and biding our time until we get sick.”