NEW YORK (NYTIMES) - Since she tested positive for Covid-19 in April 2020, Ms Josie Cabrera Taveras has found herself sleeping for up to 15 hours a day, stopping in grocery store aisles to catch her breath, lapsing in and out of consciousness and unable to return to her job as a nanny.

She believes that she is one of thousands, possibly millions, of Americans who may have a condition known as "long Covid". The Biden administration has said people with the condition could qualify for federal disability protections and benefits, which can include healthcare, housing and unemployment benefits.

But like many others who may have long Covid, Ms Taveras, 31, of New York, has had a hard time proving it.

Two brain MRIs, several heart ultrasounds, dozens of lung X-rays, two stomach endoscopies, one colonoscopy and multiple CT scans have all provided the same results: Everything looks normal.

"It's something doctors can't explain yet, what's happening to me," Ms Taveras said.

With no direct medical evidence of her condition, she has been turned down for disability coverage twice. Even a note from a prestigious post-Covid clinic in the Mount Sinai hospital system, attesting that Ms Taveras "continues to experience daily symptoms and is currently unable to work", was not enough.

In July 2021, at a White House event celebrating the Americans with Disabilities Act, US President Joe Biden promised "to make sure Americans with long Covid who have a disability have access to the rights and resources that are due under the disability law".

But with no widely agreed-on method of diagnosing the ailment, those who believe they have long Covid are finding it difficult to qualify under a system that is unfamiliar and already tricky to navigate.

Studies have shown that a significant number of Covid-19 patients continue to seek treatment for a wide range of medical conditions many months after a diagnosis. The American Academy of Physical Medicine and Rehabilitation estimates that three million to 10 million Americans may have long Covid.

Yet, many of those seeking benefits cannot produce a positive coronavirus test, which were in short supply at the beginning of the pandemic. And lab results and scans often show nothing unusual for those continuing to experience symptoms.

"I expect the tests to come back normal," said Dr Luis Tatem, an infectious-disease specialist who has been treating Ms Taveras and other long-Covid patients at the University Hospital of Brooklyn.

He added: "We're used to having a laboratory to back us up. And for this, you don't."

Since December 2020, the Social Security Administration has determined that about 16,000 applicants were able to provide medical evidence supporting Covid-19 as one of their impairments, according to Ms Nicole Tiggemann, a spokesman for the agency, which was not flagging Covid-19 cases before that.

But she would not say how many of those 16,000 applicants had been approved for benefits, or how many people claiming long Covid as a condition had been denied. Many cases are probably still pending; wait times for a determination can stretch for five months or more.

The pandemic forced the Social Security Administration to largely shut down in-person services, and some experts predict a flood of applicants with long Covid in the coming year, on top of the agency's already strained workload.

"Addressing the disability backlog is one of our top priorities," Ms Tiggemann said via e-mail, acknowledging that the pandemic had increased wait times.

Mr Biden has called for an increased US$1.3 billion (S$1.75 billion) for the agency's budget for the 2022 fiscal year, but his proposal is part of the current negotiations in Congress, and it is unclear whether it will pass.

About 8.1 million disabled workers and 1.4 million of their family workers receive disability benefits, which average about US$1,280 a month. To qualify, applicants must demonstrate a disability that substantially limits their ability to work and has lasted, or will last, for at least a year.

Typically, the Social Security Administration uses medical assessments or health records to determine whether someone qualifies, and a vast majority of those approved for disability stay on it for life.

Getting approved can be difficult. Between 2009 and 2018, the Social Security Administration denied 66 per cent of applications on average.

Long Covid has proved similar to other diseases that can be difficult to diagnose, including myalgic encephalomyelitis (also known as chronic fatigue syndrome), fibromyalgia, rheumatoid arthritis and post-treatment Lyme disease syndrome - conditions that can also cause fatigue, memory issues and joint pain.

Patients with these diseases often find it difficult to qualify for disability benefits and get accurate, timely medical diagnoses. Studies from the Centres for Disease Control and Prevention and organisations that represent people with those conditions have shown that some patients can spend years or even more than a decade trying to determine what causes their illnesses.

Many medical schools do not offer enough training on these types of diseases, and research for them is underfunded, said Ms Linda Tannenbaum, chief executive of the Open Medicine Foundation, a non-profit that funds research into chronic complex diseases like fibromyalgia and long Covid.

"Most patients cannot get disability benefits," she said.

Dr Stephen Martin, a physician and professor at the University of Massachusetts Medical School, said the complex nature of diagnosing long Covid required the coordination of various specialists who also have specific knowledge of the condition.

Many are overbooked, he said, with wait lists of more than six months - especially for patients who do not have good health insurance.

"This really hits us in our Achilles' heel of healthcare," Dr Martin said. "The American healthcare system really isn't set up to do this at scale."