The puzzle of America's record Covid hospital rate
Even as the Omicron variant sweeps around the world, public health officials have noted that, in most cases, the number of Covid patients in hospitals remains significantly lower than during previous pandemic surges.
That's not the case in the US, however, where the number of patients with the coronavirus currently in hospital has reached record numbers.
According to data from the Department of Health and Human Services, 145,982 people were in hospital with the virus on 11 January, surpassing a previous record set in January 2021.
On Thursday, US President Joe Biden was expected to announce plans to deploy military medical personnel to help in six of the states hardest hit by the influx of patients.
Similarly, hospitals in large parts of neighbouring Canada have also seen surges, with Quebec reporting a pandemic high last weekend.
So what is going on, and why might North America's experience be different to South Africa and Europe so far?
What do the numbers show?
Let's begin with this chart comparing how many people in several countries have been in hospital with Covid-19 during the pandemic. It's adjusted to account for population size and represents a ratio of the number of infected hospital patients per million inhabitants.
The various peaks represent times in which each nation was hit by a new Covid wave, including the initial outbreak and influx of hospital patients, last winter's surge or the summer spike caused by the Delta variant.
The green line, for example, shows how hard Italy was hit at both the beginning of the pandemic and again last year, reaching a high of 638 infected patients per million inhabitants on 23 November, 2020.
On the right side of the chart, every country has experienced a large spike in Covid-infected hospital patients due to Omicron. What's interesting, however, is to compare the rates each country is hitting now with those previous peaks.
For Italy, France, and the UK, we see that the number of patients in hospital with Covid remains much lower than in previous waves. In the UK, 291 patients with coronavirus per million were in hospital on 10 January. Just under a year ago, the ratio stood at 576 per million. In France, the ratio stood at 347 per million on the same day, compared with a high of 490 in November.
In the US, on the other hand, 411 US Covid-19 patients per million people were in hospital as of 9 January - surpassing a previous peak of 400 per million set on 14 January 2021.
Similarly, the data shows that in Canada, 206 people were in hospital per million as of 11 January, compared to previous peaks of 118 in April and 128 in January 2021.
What has the impact been on hospitals?
Hospitals around the US have reported that the spike in infected patients has exacerbated pressure on facilities already strained by the pandemic.
Dr Juan Reyes, the director of hospital medicine at George Washington University in Washington DC - which is among the US cities with the highest per capita hospital admissions rate - said that this surge "has been a lot more challenging" than previous ones.
"The challenge that we're feeling now is that it's happening at a larger volume and things are a little bit tighter," he told the BBC. "The difference now is a lot of fatigue, on healthcare workers and the population at large."
Dr Lewis Rubinson, the chief medical officer of Morristown Medical Center in New Jersey, reported that the current admissions surge "is about twice the size" of its previous high in the winter of 2020, despite less severe infections among patients.
He attributed the rising numbers, partially, to increased testing of everyone who comes in the hospital for any reason. In the US, UK and Canada, newly admitted patients are tested for Covid regardless of what brought them to a hospital.
Still, "the overall impact on hospitals by the sheer numbers is tremendous," he said. "[If] you take off even a third of those, it's still an enormous amount of patients that we're tackling."
In the UK, this proportion of so-called incidental Covid cases has been estimated by National Health Service bosses to be between 20-30% of cases.
What's happened in South Africa?
In South Africa - where the Omicron variant was first detected in November - researchers found that those infected with Omicron are less likely to be sent to hospital and more likely to recover quickly.
While up-to-date data regarding the rate of Covid patients in hospital per capita is not available, many South African hospitals reported that the number was significantly less than during previous surges.
The Steve Biko Academic Hospital in the City of Tshwane, for example, reported to the International Journal of Infectious Diseases that the number of infected patients was about half of that recorded before mid-November.
Researchers believe that South Africa's previous Covid-19 waves and relatively low vaccination rate meant that many residents had already likely been exposed and had built up some level of immunity.
Why is the US different?
Experts point to several reasons why the rate of Covid patients in hospital is higher in North America than in most other parts of the world.
Professor David Larsen, an epidemiologist and global health expert at Syracuse University in New York, told the BBC that the US population is markedly different from that of both Europe and South Africa.
"We have an older population than South Africa. That's a big one," he said. "[The US] is kind of similar in age structure to Europe. But there's also a less healthy population than in Europe."
As examples, Dr Larsen noted that rates of hypertension and obesity - both of which are comorbidities that increase the risk of Covid - are higher in the US than in most other countries.
Dr Larsen added that "it's incredibly frustrating" to hear Americans downplay the ongoing threat of Omicron and believe that, like South Africa, the US may soon emerge from the current surge.
"The seasonality is also different," he said. "Omicron's surge through South Africa was during their summer, and it's hitting us in winter when we know more people gather indoors and there's more transmission…it's going to be bad."
Dr Mark Cameron, an associate professor in the department of population and quantitative health sciences at Case Western University in Ohio, told the BBC that he believes the US is suffering from "a perfect storm" of Covid-19, comorbidities, uneven access to healthcare and hostility to vaccines, masks, and other preventative measures.
"When all of that 'perfect storm' nature of vulnerabilities that are unique to the US combine, you've got an outbreak of the virus that can quickly lead from increased cases to increased hospitalisations, which tax the local hospitals and health community."
Just over 63% of the US population is fully vaccinated, much lower than in the UK (71%) as well as Italy and France (both 75%). In Canada, almost 79% of the population is fully protected.
What about Canada?
Dr Donald Vinh, an infectious disease specialist at McGill University Health Centre in Montreal, said that in Quebec - and other places across Canada - as many as half of all new hospital admissions are among the "inadequately vaccinated".
"As a percentage of the population, it's a low number. Maybe 10% of the eligible population are not doubly vaccinated," he said. "They tend to be clustered in urban dense spots. When you have highly transmissible variants and it can affect an inadequately vaccinated population, this leads to ongoing propagation and the high community transmissions we're seeing."
Like the US, Dr Vinh said that he believes Canada is plagued by an "incongruent" public health policy when it comes to Covid-19.
"In other words, there isn't a single unified method in how we're going to do things across the board," he said. "It's more regional than national, and because of that you have gaps. The consequences of that are people getting hospitalised."
What about the Delta variant?
Doctors also warn that the high level of hospital admissions in the US and Canada may be due to the Delta variant being more prevalent in many areas.
A study published in August by The Lancet Infectious Diseases - which investigated 43,000 patients in the UK - found that the Delta variant had more than double the risk of hospital admission than previous variants.
Dr Monica Gandhi, an infectious diseases physician and professor at the University of California San Francisco, said that while she believes Delta patients form a significant portion of Covid-19 hospital admissions in the US, the true figure is hard to determine.
"We don't know how much Delta there is," she told the BBC. "What the US has started to do is look at the number of new infections and sequences. Omicron is 95% of new infections, but we don't know how much Delta we still have around."
In her own hospital, Dr Gandhi added, some patients "are sicker and some are less sick, and that feels very much like Delta and Omicron are both there".
In many countries, researchers believe that the Omicron variant has begun to subside, possibly signalling the end of the increase in hospital patients with Covid.
A computer model from researchers at the University of Washington, for example, has projected that the number of daily cases in the US will reach a high of 1.2 million by 19 January. Some researchers have predicted that cases may even peak sooner.
In the short-term, however, experts believe that hospitals will continue feeling the strain of elevated patient numbers in both the US and Canada, even as they fall in other countries.
"The situation is bad. There's really no other word to describe it," Dr Vinh said of the pandemic in Canada. "I would love to start seeing an inflection point that tells us we're at the plateau, but right now all I'm seeing is a hill. It's not even a hill anymore. It's a wall."
Dr Larsen, for his part, said he believes that the US needs "more urgency around systemic change" to move past Covid-19.
In the US, both Dr Cameron and Dr Gandhi suggested that they believe hospital admissions may peak in February or March.
"It still could make for a miserable winter," Dr Gandhi said. "I think that for the next month, life is going to be really hard in schools and hospitals."