The New York Times
07/05/2020 - 15:20
- Clarín.com
- World
More than six months after the pandemic, the coronavirus has infected more than 11 million people worldwide, killing more than 525,000. But despite the growing number, scientists still don't 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 occur if the virus spread out of control. The figure, generally called the infection death rate, 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 difficult budget choices are routine, the number could help officials decide whether to spend more on oxygen concentrators or ventilators , or on vaccines against measles and mosquito nets.
The question became even more complex last month, when the Centers for Disease Control and Prevention released data suggesting that for every documented infection in the United States, there were 10 other cases on average that went unrecorded, likely because they were very mild or asymptomatic. .
If there are many more asymptomatic infections than previously thought, then the virus may be less deadly than it sounds. But even that calculation is difficult.
On Thursday, after the World Health Organization held a two-day online meeting of 1,300 scientists from around the world, the agency's chief scientist, Dr. Soumya Swaminathan, said the consensus for now was that the IFR is approximately 0.6%, which means that the risk of death is less than 1%.
Although she did not notice this, 0.6% of the world population is 47 million people, and 0.6% of the United States population is 2 million people . The virus remains a major threat.
Currently, countries have very different case fatality rates, or CFRs, that measure deaths among patients known to have had COVID-19. In most cases, that number is higher in countries that have had the virus for the longest time.
According to data compiled by The New York Times , China had reported 90,294 cases as of Friday and 4,634 deaths, representing a CFR of 5%. The United States was very close to that mark. It has had 2,811,447 cases and 129,403 deaths, about 4.6%.
Those percentages are much higher rates than the 2.5% death rate often attributed to the 1918 flu pandemic . Still, it is difficult to measure mortality rates during pandemics, especially in the beginning.
In the chaos that ensues when a new virus hits a city, thousands of people can die and be buried without testing , and certainly without autopsy.
It is never entirely clear how many died from the virus and how many died from heart attacks, strokes, or other ills. That has happened in both New York City and Wuhan, China, where the outbreak began.
What is Coronavirus? How is it spread and what are its symptoms?
Watch the specialTypically, once the chaos has subsided, more testing is done and more mild cases are found, and because the denominator of the fraction increases, death rates decrease. But the results are not always consistent or predictable.
Ten major countries, most of them in Western Europe, have tested higher percentages of their populations than the United States, according to Worldometer, which compiles statistics. They are Iceland, Denmark, Spain, Portugal, Belgium, Ireland, Italy, Great Britain, Israel and New Zealand.
But their case fatality rates vary enormously: Iceland is less than 1%, New Zealand and Israel are below 2%. Belgium, by comparison, is at 16%, and Italy and Great Britain at 14%.
Both figures, the mortality rate from infection and the case fatality rate, may differ greatly by country.
So far, in most countries, about 20% of all COVID-19 confirmed patients have become sick enough to need supplemental oxygen or even more advanced hospital care, said Dr. Janet Díaz, chief clinical care officer. from the WHO emergency program. Whether these patients survive depends on a number of factors, such as age, underlying diseases, and the level of medical care available.
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Mortality rates are expected to be lower in countries with younger populations and less obesity, which are often the poorest countries. Conversely, the numbers 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 struggling to buy oxygen equipment for the poor and middle-income nations where 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 become seriously ill could change risk estimates. Type A blood is relatively rare in West Africa and South Asia, and very rare among the indigenous peoples of South America.
Ahead of last week's meeting, the WHO did not have an official IFR estimate, Oliver Morgan, the agency's director of health emergency information and risk assessment, said in an interview in early June.
Instead, it had been based on a combination of data submitted by member countries and academic groups, and a meta-analysis conducted in May by scientists from the University of Wollongong and James Cook University in Australia.
Those researchers analyzed 267 studies in more than a dozen countries, and then chose the 25 they considered most accurate, weighting them for their precision and averaging the data. They concluded that the global IFR was 0.64%.
The CDC estimate for the United States is lower: an IFR of 0.4%, based on a set of planning scenarios released in late May. The agency did not respond to requests to explain how it reached that figure, or why it was much lower than WHO estimates. In comparison, 0.4% of the US population is 1.3 million people.
The 25 studies that Australian researchers considered to be the most accurate were based on very different methodologies. One report, for example, was based on PCR diagnostic tests of all passengers and crew aboard the Diamond Princess, the cruise ship that docked in Japan after it was overtaken by the coronavirus. Another study extracted data from an antibody survey of 38,000 Spaniards, while another included only 1,104 Swedes.
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, WHO's Morgan said.
To arrive at the CDC's new estimate, the researchers analyzed samples from 11,933 people to detect antibodies against the coronavirus in six regions of the U.S. New York City reported 53,803 cases as of April 1, but the actual number of Infections was 12 times higher, almost 642,000, the agency estimated.
The New York City prevalence of 7% in the CDC study was well below the 21% estimated in a state survey in April. But that number was based on people recruited from supermarkets, so the results may have been biased toward people who go shopping during a pandemic, often young people, who have been less affected.
Global death rates could still change . With one or two exceptions, such as Iran and Ecuador, the pandemic first hit the wealthiest countries in Asia, Western Europe, and North America, where advanced medical care was available.
It is now spreading widely in India, Brazil, Mexico, Nigeria, and other countries where millions are full of slums, closings have been relatively brief, and hospitals are under-resourced.
But death rates may also change in the wealthier countries of the north as winter approaches . Most of the spread of the virus in Europe and North America has occurred during temperate or warm weather in spring and summer.
Many experts fear infections and deaths will skyrocket in the fall as colder weather forces people to enter, where they are more likely to infect each other. Discipline on wearing masks and avoiding breathing with each other will be even more important .
Donald G. McNeil Jr. The New York Times