January 9 will mark three years since the first death in China from Covid-19 — and since then millions more have died.
The coronavirus spread quickly across the globe after emerging in Wuhan and within a few months was causing tens of thousands of deaths each week.
The official toll stands at more than 6.6 million and the virus continues to kill thousands of people each week.
But current circumstances are much improved.
University of East Anglia
Most societies that imposed lockdowns have opened up and, from around the second quarter of last year onwards, the global death rate has been stable and much lower than during most of the previous two years, even if Covid hospital admissions continue to put healthcare systems under strain.
China is a notable exception, with the country’s recent opening up after three years of tight restrictions causing cases, and possibly deaths, to surge.
Outside China, many populations are now less at risk than at the start of the pandemic.
Increased immunity
About 69.1 per cent of the world's population has received at least one dose of a Covid-19 vaccine, according to OurWorldinData, and 13.18 billion doses have been administered in total.
On top of that, the 657 million cases of Covid-19 to date — according to official figures, which are likely to heavily underestimate the real number — mean that much of the world’s population has immunity from prior infection.
In Europe, for example, people "still have some background immunity" that provides protection, according to Prof Eskild Petersen, of Aarhus University Hospital in Denmark and chairman of the European Society of Clinical Microbiology and Infectious Diseases.
"If you envisage an entirely different virus with higher pathogenicity, it would have to be very different not to be covered by the immunity now," he said.
"If you have high vaccine coverage — three or four doses — you are very, very well protected and you will have a certain number of people with further immunity from natural infection. That’s the difference from spring 2020, when nobody had any immunity."
Coupled with that, Covid-19 is widely seen to have become less virulent thanks to the easily transmitted but milder Omicron strain and related variants, which are responsible for most infections now.
"Gradually, since the appearance of Omicron, the severity has got a lot less than even a year ago," said Paul Hunter, professor in medicine at the University of East Anglia in the UK.
"We’re not seeing nearly as many admissions to hospitals or people in intensive care beds. Now it’s less severe than flu. If you catch Covid, you’re less likely to die than with flu."
Better prepared
With the world emerging from what is often seen as the worst pandemic for a century, many researchers hope there will be better preparations for the next emergence of a new disease.
The last major pandemic of a scale comparable to Covid-19 involved Spanish flu and began in 1918, but it is unlikely, said John Oxford, emeritus professor of virology at the University of London, that it will be another century before the world faces something similar.
"It doesn’t have to be China, France or the US — it can happen anywhere," he said. "The key thing is to know it will happen again and to stockpile PPE [personal protective equipment].
"You have to have a plan and have someone guarding the plan. The plan must be updated and have a proper guardian to keep the finance coming in for it. It’s essential. It needs more than science to keep it marching along.
"All countries were begged by the World Health Organisation to get a plan. Some had three pages, some 150 pages."
The world is now, however, "biologically more sophisticated", with improved vaccination and monitoring capability, so is better able to react to pandemics, suggested David Taylor, emeritus professor of pharmaceutical and public health policy at University College London.
"We need to invest, but we don’t want to invest in old-style public health," he said. "We need intelligent biological surveillance … based on better understanding.
"We need leaner, sensible investment in high-level planning for pandemic possibilities, but remembering there are so many other things that could go wrong.
"We have global warming — unless we get energy and climate change sorted, that will almost certainly kill us in the next century … we have a real problem to sort."
Scientific advances
While the pandemic has left a legacy of suffering, death, societal upheaval and economic damage, it has helped accelerate scientific advancement.
There had been decades of work to develop messenger RNA (mRNA) vaccines, but it was not until Covid-19 that these were actually introduced to protect people from disease.
Writing in the journal Viruses last year, researchers said the pandemic had "opened the floodgates to mRNA vaccines’ potential in infectious disease prevention", with many animal as well as human diseases the focus of emerging vaccines.
Therapeutic mRNA vaccines for diseases such as cancer are also becoming a reality, with more clinical trials beginning.
The pandemic also led to the successful use of vaccines, such as the Oxford-AstraZeneca dose, that use a weakened chimpanzee adenovirus as a vector. This causes the cells of recipients to produce coronavirus spike proteins, leading to a protective immune response.
The pandemic has improved scientists’ wider understanding of viral illnesses, according to Prof Hunter, who said it has helped his own work on noroviruses which cause gastroenteritis.
"There are actually a lot of positive things that have come out of this pandemic in science," he said. "The downside is a lot of people have had to die for it. I would rather we had not had the pandemic and remained ignorant."
"But there are things we can take from the pandemic that will help us understand infectious diseases and help us reduce the risk of severe diseases in the future. And new vaccinations put together more quickly could have very wide implications.
"Because so much money and research has gone into it, we know things about Covid that we sort of knew about other infections, such as the duration of mucosal immunity [immunity in the moist inner lining of, for example, the nose and lungs] following infection and vaccination."
As to how the pandemic will continue to play out, Prof Hunter said he expected the coronavirus would continue to become less severe in its effects until it became another cause of the common cold. Other coronaviruses already cause about 10 to 15 per cent of colds.
That does not mean, however, that it will not carry on killing people, because, Prof Hunter noted, even the common cold can trigger chest infections, albeit less often than influenza does.
"I think over the next few years hospitalisations will become a lot less common and deaths a lot less common as well," he said.
