Key question: How deadly is coronavirus?
Scientists struggle to answer even after 500,000 deaths
More than six months into the pandemic, the coronavirus has infected more than 11 million people worldwide, killing more than 525,000. But despite the increasing toll, scientists still do not have a definitive answer to one of the most fundamental questions about the virus: How deadly is it?
A firm estimate could help governments predict how many deaths would ensue if the virus spread out of control. The figure, called the infection fatality rate (IFR), could tell health officials what to expect as the pandemic spreads to densely populated nations like Brazil, Nigeria and India.
In even poorer countries, where lethal threats like measles and malaria are constant and where hard budget choices are routine, the number could help officials decide whether to spend more on oxygen concentrators or ventilators, or on measles shots and mosquito nets.
The question became even more complex last month, when the Centres for Disease Control and Prevention (CDC) released data suggesting that for every documented infection in the United States, there were 10 other cases on average that had gone unrecorded, probably because they were very mild or asymptomatic.
If there are many more asymptomatic infections than once thought, then the virus may be less deadly than it has appeared. But even that calculation is a difficult one.
On Friday, after the World Health Organisation held a two-day online meeting of 1300 scientists, the agency’s chief scientist, Dr Soumya Swaminathan, said the consensus for now was that the IFR is about 0.6 per cent — which means that the risk of death is less than 1 per cent.
Although she did not note this, 0.6 per cent of the world’s population is 47 million people. The virus remains a major threat.
Countries have very different case fatality rates (CFRs), which measure deaths among patients known to have had Covid-19. In most cases, that number is highest in countries that have had the virus the longest.
According to data gathered by The New York Times, China had reported 90,294 cases as of Saturday and 4634 deaths, which is a CFR of 5 per cent. The United States was close to that mark. It has had 2,811,447 cases and 129,403 deaths, about 4.6 per cent.
Those percentages are far higher rates than the 2.5 per cent death rate often ascribed to the 1918 flu pandemic. Still, it is difficult to measure fatality rates during pandemics, especially at the beginning.
When a new virus hits a city hard, thousands of people may die and be buried without ever being tested, and certainly without them all being autopsied. It is never entirely clear how many died of the virus and how many died of heart attacks, strokes or other ills. That has happened in New York City and in Wuhan, China, where the outbreak began.
Normally, once the chaos has subsided, more testing is done and more mild cases are found — and because the denominator of the fraction rises, fatality rates fall. But the results are not always consistent or predictable.
Ten sizeable countries, most of them in Western Europe, have tested bigger percentages of their populations than has the United States, according to Worldometer, which gathers statistics. They are Iceland, Denmark, Spain, Portugal, Belgium, Ireland, Italy, Britain, Israel and New Zealand.
But their case fatality rates vary wildly: Iceland’s is less than 1 per cent, New Zealand’s and Israel’s are below 2 per cent. Belgium is at 16 per cent, and Italy and Britain at 14 per cent.
Both figures — the infection fatality rate and the case fatality rate — can differ quite a bit by country.
So far, in most countries, about 20 per cent of all confirmed Covid-19 patients become ill enough to need supplemental oxygen or even more advanced hospital care, said Dr Janet Diaz, head of clinical care for the WHO’s emergencies programme.
Whether those patients survive depends on a host of factors, including age, underlying illnesses and the level of medical care available.
Death rates are expected to be lower in countries with younger populations and less obesity, which are often the poorest countries. Conversely, the figures should be higher in countries that lack oxygen tanks, ventilators and dialysis machines, and where many people live far from hospitals. Those are also often the poorest countries.
The WHO and various charities are scrambling to purchase oxygen equipment for poor and middleincome nations in which the coronavirus is spreading.
And now, new factors are being introduced into the equation. For example, new evidence that people with Type A blood are more likely to fall deathly ill could change risk calculations. Type A blood is relatively rare in West Africa and South Asia, and very rare among the indigenous peoples of South America.
Before this past week’s meeting, the WHO had no official IFR estimate, Oliver Morgan, the agency’s director of health emergency information and risk assessment, said.
Instead, it had relied on a mix of data sent in by member countries and by academic groups, and on a metaanalysis done in May by scientists at the University of Wollongong and James Cook University in Australia. They concluded that the global IFR was 0.64 per cent.
The best estimate for the US is 0.4 per cent, according to a set of planning scenarios released by the CDC in late May. The agency did not respond to requests to explain how it arrived at that figure, or why it was so much lower than the WHO’s estimate. By comparison, 0.4 per cent of the US population is 1.3 million people.
The current WHO estimate is based on later, larger studies of how many people have antibodies in their blood; future studies may further refine the figure, Swaminathan said.
But there is “a lot of uncertainty” about how many silent and untested carriers there are, Morgan said.
The global fatality rates could still change. With one or two exceptions, like Iran and Ecuador, the pandemic first struck wealthier countries in Asia, Western Europe and North America where advanced medical care was available.
Now it is spreading widely in India, Brazil, Mexico, Nigeria and other countries where millions are crowded into slums, lockdowns have been relatively brief and hospitals have few resources.
But the death rates may also shift in wealthier northern countries as winter approaches. Most of the spread of the virus in Europe and North America has taken place during mild or warm weather in the spring and summer.
Wearing masks and avoiding breathing on one another will be even more important then.