NEW YORK (NYTIMES) - At the onset of the coronavirus pandemic in 2020, scarce ventilators and protective equipment faced strict rationing. Today, as the pandemic rages into its third year, another precious category of products is coming under tight controls: treatments to stave off severe Covid-19.

There is a greater menu of Covid pills and infusions now than at any point in the pandemic. The problem is that the supplies of those that work against the Omicron variant are extremely limited.

That has forced state health officials and doctors nationwide into the fraught position of deciding which patients get potentially life-saving treatments and which don't. Some people at high risk of severe Covid are being turned away because they are vaccinated.

Some hospitals have run out of certain drugs; others report having only a few dozen treatment courses on hand. Staff are dispensing vitamins in lieu of authorised drugs. Others are scrambling to develop algorithms to decide who gets treatments.

"There is simply not enough to meet the needs of everyone who is going to have Covid in the upcoming weeks and be at risk of severe complications," said Dr Natasha Bagdasarian, Michigan's chief medical executive. "I don't think there is a way to make sure it gets to all the right people right now."

At Family Health Centres of San Diego, a network of clinics for low-income patients, the staff has had to turn away about 90 per cent of the hundreds of people who are calling daily and are eligible for Covid treatments.

"It makes me nauseous going home at night because it makes me feel like I'm deciding, with this limited resource, who should get it," said Dr Christian Ramers, an infectious disease specialist there.

A plentiful supply of effective treatments would be a powerful weapon as the virus again surges across the United States. Fuelled by the highly contagious Omicron variant, Covid cases have soared to record highs, and the number of hospitalised patients also has increased sharply, although Omicron tends to cause milder illness than other variants.

For most of the pandemic, monoclonal antibodies - a treatment generally administered intravenously at hospitals or clinics - have been the primary option for recently infected patients.

But the two most common types of the antibodies don't appear to work against the Omicron variant, which is quickly becoming the world's dominant version of the coronavirus.

There is a third antibody treatment, made by GlaxoSmithKline and Vir Biotechnology, that is potent against Omicron. But the federal government has ordered only about 450,000 treatment courses, many of which have already been used or have not yet been delivered to states.

The Food and Drug Administration (FDA) two weeks ago authorised the use of a new antiviral pill, developed by Pfizer, that shows great promise at fighting Covid in general and Omicron cases in particular.

The federal government is providing the pill, known as Paxlovid, to states, whose health officials decide where to send the pills and how to advise doctors to use them.

Supplies are already being depleted. New York City, for example, received about 1,300 treatment courses of Paxlovid in late December, which it used up within a week, according to a spokesperson for Alto Pharmacy, which is distributing the city's supply. New York City currently does not have any Paxlovid in stock.

On Tuesday (Jan 4), the US government doubled its order for Paxlovid, although supplies won't be plentiful until April.

State and local officials say the goal is to get Paxlovid to as many of the most vulnerable people as possible, with a particular focus on those with weakened immune systems or who are unvaccinated.

Unvaccinated people are at far greater risk of hospitalisation or death from Covid. But giving them priority access to treatments leaves people feeling "like you are rewarding intransigence," said Dr Matthew Wynia, the director of the Centre for Bioethics and Humanities at the University of Colorado, who has advised the state on how to ration Covid treatments.

Only some states, like Ohio and Nevada, have sent Paxlovid to pharmacies that serve nursing homes, whose residents are especially vulnerable to Covid. Many states, including Virginia, Pennsylvania and Arizona, have sent most or all of their initial Paxlovid supplies to pharmacy chains like Walgreens and Rite Aid.

That was meant to make the pills as widely accessible as possible. But the system rewards patients who have the time, energy and savvy to chase down treatments.

Mr Patrick Creighton, 48, a sports radio host in Katy, Texas, woke up on New Year's Eve with his throat burning. He was vaccinated but tested positive later that day. Concerned that his diabetes elevated his risk of becoming seriously ill, he decided to seek out Paxlovid, which he had been reading up on.

A telemedicine doctor wrote him a prescription the next day. Now he needed to find a pharmacy with Paxlovid in stock. He said he called 18 pharmacies within driving distance: one Brookshire Brothers, four Krogers, four H-E-Bs, three Walgreens, three CVS stores and three Walmarts. None had the pills.

His 19th call was a winner: A nearby Walmart had Paxlovid in stock. The ordeal still wasn't over. He was incorrectly told that he might have to pay US$500 (S$680) for the free treatment.

Then he had to see a second telemedicine doctor because of a problem with the way his prescription was sent. Then his wife had to make a second trip to Walmart to pick up the pills. But on the evening of Jan 2, he finally took the first three tablets of the 30-pill regimen.

Mr Creighton said he worried about patients who weren't able to navigate the obstacles like he could. "It should be easily obtainable for everybody," he said.

The GlaxoSmithKline antibody treatment is similarly hard to come by.

At the University of Pittsburgh Medical Centre, the staff is now giving out 400 to 800 antibody treatments each week, down from 2,000 to 3,000 before Omicron rendered two of the products useless. Demand has rocketed higher, but the hospital no longer has enough supply.

"It is devastating to tell these patients, 'Sorry, we can't do anything for you, we have to save this drug only for our most severely immunocompromised,'" said Ms Erin McCreary, an infectious diseases pharmacist at the hospital.

Mr Louis Shantzek, a Miami retiree, tried unsuccessfully to get an antibody infusion last week after he tested positive for the virus. He is 72 and has diabetes and a heart condition - all factors that would normally make him eligible to get an antibody treatment.

Mr Shantzek's symptoms included aches, fatigue and a bad cough. When his adult daughter called two nearby hospitals, she was told he couldn't get an antibody infusion because he had received three doses of a vaccine and was therefore considered at relatively low risk.

"It's like being told, 'You're doing everything you're supposed to do, but yet we're not going to help you,'" said Mr Shantzek, whose symptoms have since eased.

This is not the first time in the pandemic that scarce supplies have forced hospitals and doctors into painful treatment decisions. Early on, an intravenous treatment, remdesivir, became so popular that hospitals had to restrict its use. Supplies of remdesivir have since become more plentiful, but the treatment is primarily used for patients who are already hospitalised with severe Covid.

An increasing number of hospitals are imposing restrictions on treatments.

In western Indiana, officials at Sullivan County Community Hospital determined last month that they had to restrict eligibility for antibody infusions, after weeks of receiving far fewer doses than they had ordered. They opted to almost exclude vaccinated people.

Dr Shireesha Dhanireddy, an infectious disease specialist at the University of Washington, said she spent last weekend poring over the charts of Covid patients to figure out who should get scarce treatments. T

he three-hospital system has tens of thousands of patients but only 60 courses of Paxlovid. Those getting the pills include patients on certain types of chemotherapy and those who recently received organ transplants.

At Johns Hopkins University, employees are rushing to develop algorithms to help allocate scarce treatments, said Dr Kelly Gebo, an infectious diseases and epidemiology specialist. Compounding the scarcity problem, workers are falling ill, making it harder to deliver resource-intensive treatments like monoclonal antibodies.

"It's demoralising as health care workers when we can't deliver optimal care when we have limited resources," she said.