Coronavirus has now claimed the lives of one million people across the globe. But the death toll is likely to reach two million unless we get the pandemic properly under control, a senior World Health Organisation official has warned.
As the world passed the grim milestone on Tuesday morning Dr Mike Ryan, head of emergencies at the WHO, said it was "not impossible" another one million people could die before a vaccine becomes available, while better treatments and effective vaccines might not be enough on their own to prevent deaths surpassing two million.
"Are we prepared to do what it takes to avoid that number?" Dr Ryan asked. "Unless we do it all, the number you speak about is not only imaginable, but unfortunately and sadly, very likely."
The Covid-19 pandemic is now on a par with the 1889-90 global influenza pandemic. In the UK, the Government's chief scientific advisers warned that, without any action, Covid-19 cases could hit 50,000 a day by next month, bringing with it 200 daily deaths.
So much is still unknown about the nature of the disease. To what extent will immunity help prevent further deaths? How reliable is the data underpinning the global response to the virus? Will a new vaccine developed in China hold the key?
As fatalities continue to climb, the Telegraph asks three experts what could happen next.
While the alarm was first sounded in Asia, the time lapse map above shows how the pandemic spread across the world, taking a firm hold in Europe during the spring.
More than 40,000 people have died in the United Kingdom – the highest death toll in Europe.
But it didn't take long for the first wave to grip the Americas, where it hit the hardest. More than 200,000 people have now lost their lives to the virus in the United States, and more than 100,000 in Brazil.
Peru, where more than 30,000 have died, has one of the highest death rates in the world at more than 98 deaths per 100,000 people.
The virus is now returning to Asia, with huge losses across India. According to the latest data, Asia accounted for 35 per cent of new deaths globally in the week up to September 23, up from 24 per cent a month ago.
Deaths are rising fastest in the east. In Asia, an average of 1800 deaths a day were recorded during the week to September 23.
In the same period, South America saw an average of close to 1500 deaths a day, and in North America that was nearer 1200.
Meanwhile in Europe, once the epicentre of the pandemic and with some of the highest cumulative deaths rates, the continent has been averaging fewer than 550 deaths a day.
But the rate is now beginning to climb, up from 450 a day a week ago. The fear is those numbers could rise steeply again as infections grow exponentially – in other words, as the number of new infections double over a fixed time period.
This is why so many countries have reimposed social distancing restrictions and second lockdowns recently in an attempt to "circuit break" the recent growth in cases.
So what will happen next? Here's what the experts said:
'An increase in deaths is inevitable'
Devi Sridhar, professor of global public health, University of Edinburgh
"Deaths are still going to continue to climb as the number of new cases hasn't levelled off and we haven't reached the peak yet. In countries like Brazil, India, Russia and the US the disease is not under control.
"Realistically, we're still going to see more cases and deaths to come, especially as we hit winter in the northern hemisphere.
"At the beginning of the pandemic, people asked: 'What is South Korea and Germany's secret? How did they keep deaths low?' But they had early intervention and could offer top medical care.
"But if hospitals become overwhelmed and people aren't admitted, then the case fatality rate [CFR] will increase because survival depends on medical care.
"Now, the CFR is about 0.6 per cent and people are saying the disease isn't that serious. But the CFR will stay low only if people can get care when they need it.
"In developing countries, it's hard to predict what will happen. In Africa, the pandemic has not hit as we predicted. Having read across the literature, there's not one proven conclusion. In sub-Saharan Africa, countries reacted really quickly and many shut their borders before they had even one case.
"In India the virus ripped through slums, but the fatality was not that high. In these very poor contexts, there's already been some kind of self-selection. These communities face continuing infectious disease outbreaks – TB, malaria, diarrhoea and pneumonia – and you have a young population. When the virus came, many of the vulnerable would already have been taken out by that – this doesn't happen in high income countries.
"There's a six to seven-week lag between a case and a death, so I think we will continue to see numbers climbing – these big increases in cases here and in Europe will see deaths later down the line. The pandemic has a way to go, so sadly an increase is inevitable."
'It could easily spin out of control'
Martin McKee, professor of European public health, London School of Hygiene and Tropical Medicine
"At the minute, case numbers are doubling every week and the really important point is that we're talking about exponential growth – so if nothing else changes you get one case, then two, four, eight, 16, etc. The rate of increase in absolute numbers is accelerating, so numbers can increase very quickly and the pandemic can easily spin out of control.
"We understand the disease a lot better now and know more about its transmission. We know it collects in the mouth and saliva, so being indoors with other people who may be infected is not going to be a good idea over the winter.
"We have also had a substantial improvement in treatment outcomes – at the beginning, everyone thought it was a viral pneumonia but then people realised blood was clotting and doctors put people on anti-coagulants and the steroid dexamethasone. Survival rates have definitely been improving.
"In Africa, there seems to be some protective immunity and there is a suggestion that people who have had parasitic worm infections have some kind of immunity – but the big factor in Africa affecting death rates is low levels of obesity.
"In Latin America, there are high levels of obesity and so you see high numbers of deaths in places like Peru and Ecuador.
"There is also a lot of variation in how people record deaths – you have to be very careful with the data. In the UK, reporting is changed so a death is counted as someone who dies within 28 days of having a positive test. But that's not that reliable. What everyone is now recognising is that the best way to measure deaths is excess all-cause mortality."
'We are by no means out of the woods yet'
Charlie Whittaker, researcher in infectious disease epidemiology, Imperial College, London
"We have an increasing number of effective drugs which, accompanied by improved clinical management, has contributed to reductions in Covid-19 mortality.
"The average age of cases has also dropped [seen in the chart below]. Early on in the epidemic, a lot of our cases and associated deaths were in elderly populations. Now more young people are being affected and they have a lower, though not non-existent, risk of severe disease and death.
"But that doesn't mean that good news is necessarily on the horizon – because if you look at what's happened with some US states, like Florida, increases in cases in younger age groups tend to be followed by spread to other groups, specifically the elderly, the vulnerable and those most at risk from Covid-19.
"And we're now beginning to see that in the UK, where hospitals admissions have also begun to increase.
"As we've seen across Europe, a lot of the gains that we've made in terms of suppressing the virus and reducing mortality are fragile. And we're by no means out of the woods just yet.
"Many countries in sub-Saharan Africa took rapid and decisive steps to curb spread of the virus and avoid large scale epidemics like we've seen across Europe to date – it's quite possible they haven't felt the full force of the pandemic, although it's difficult to tell.
"The quality of the systems that exist for reporting deaths vary so much between countries. Syria's an example of this: if you look at officially reported Covid-19 deaths coming out of Damascus, less than 100 have been reported since the first one back in March.
"Work we've carried out with Syrian doctors, however, examining excess mortality statistics and other sources of death data, including Facebook memorial groups, suggests as many as 4500 deaths, meaning that only about one in 80 Covid-19 deaths has been included in the official mortality statistics coming out of the country.
"Lingering limitations in testing capacity and the difficulty of recording deaths outside hospitals in settings like these make accurate detection of the true burden challenging.
"This highlights the extent to which Covid-19 might have spread unobserved across many parts of the world that don't have the necessary systems in place to accurately capture patterns of mortality."
Two million deaths by the turn of the New Year
Epidemiologists have the unenviable task of trying to predict how the virus will take shape in the coming weeks and months.
According to projections collected by the Centres for Disease Control and Prevention (CDC), the death toll in the United States could climb by more than 20,000 to more than 225,000 by October 17.
Some models predict much higher deaths tolls, with Texas Tech University projecting 244,000 deaths by mid-October.
And analysis carried out by Imperial College, London, estimates that, over the next week, five countries will accumulate more than 1000 additional deaths each – Brazil, India, Mexico, Columbia and Argentina.
The number of new deaths being reported in India alone is expected to pass 8,500 a week.
Most models err on the side of caution and do not publish estimates further than a few weeks ahead, due to the sheer number of variables involved.
But models projecting the spread of the virus up to the end of the year have been made by the Institute for Health Metrics and Evaluation (IHME).
At the most conservative estimate, the global death toll is expected to pass two million by the turn of the New Year.
The team project that some of the hardest-hit world regions will include South Asia, Europe and Central Asia, with deaths anticipated to climb above 600,000 in each region.
More conservative estimates put the tally at below 500,000 in each region.
It is impossible to know exactly what the death toll will be, of course. What experts do agree on is that the impact of the virus will get worse and more people will lose their lives.
Last month, WHO director general, Dr Tedros Adhanom Ghebreyesus, said the pandemic could last up to two years.
"We have a disadvantage of globalisation, closeness, connectedness, but an advantage of better technology, so we hope to finish this pandemic before less than two years," he said.
By "utilising the available tools to the maximum and hoping that we can have additional tools like vaccines, I think we can finish it in a shorter time than the 1918 flu", he added.
Only time will tell.