US, WASHINGTON (ORDO NEWS) — The coronavirus epidemic will last a long time. This is supported by a number of new studies from around the world to determine the exact number of cases.
Official statistics often underestimate the number of cases. But even in new studies with larger tests, the proportion of infected remains within 10%. The exact threshold of group (or “herd”) immunity is not yet clear, but some experts believe that it will not be lower than 60%.
Percentage of population with antibodies to coronavirus
New York 19.9% (May 2)
London 17.6% (May 21)
Madrid 11.3% (May 13)
Wuhan 10% (April 20)
Boston 9.9% (May 15)
Greater Stockholm 7.3% (May 13)
Barcelona 7.1% (May 13)
Studies show that even in the most affected cities in the world, the vast majority of residents are still vulnerable to the virus.
Some countries, in particular Sweden and the UK for some time, refrained from mass quarantine in an attempt to develop population immunity. But even there, the proportion of infected people ranges from 7 to 17%. In New York, where the largest outbreak of coronavirus in the United States was recorded, as of early May, about 20% of residents were infected, the city hall reports based on samples taken in shops and public places.
Similar studies are being conducted in China, where the coronavirus originated, but the results are not yet published. However, as a study in a hospital in Wuhan showed, about 10% of those who want to return to work were ill with the virus.
In total, studies suggest that we are unlikely to achieve collective immunity in the near future, says Michael Mina, an employee of the Chan epidemiological school at Harvard University.
The threshold of collective immunity to a new disease has not yet been precisely determined, but many epidemiologists believe that it will not come before 60 to 80% of the population is infected and the body develops resistance or resistance. A lower level of immunity among the population may somewhat slow down the spread of the disease, but mass outbreaks can be completely ruled out only after reaching population immunity.
“Honestly, we don’t have a safe way to reach him, at least not in the shortest possible time,” says Dr. Mina. “Otherwise, it will be necessary to remove all restrictions and let the virus walk, but it seems to me that society has decided that this option does not suit us.”
New studies are aimed at finding antibodies in the blood of people, these proteins produced by the immune system indicate an infection. The advantage of this method is that it covers asymptomatic carriers that do not even know that they have already been ill. The disadvantage is that these tests are sometimes erroneous. Several studies, including one notorious one from California, have already scolded for margin of error and selectivity.
Representative serologic studies are conducted across America and around the world.
These studies are far from perfect, admits Carl Bergström, professor of biology at the University of Washington. But collectively, he says, they provide a more adequate idea of how widespread the coronavirus has spread – and what is the potential for a further epidemic.
According to him, the threshold of population immunity varies depending on the place and such factors as population density and social interaction. But on average, a minimum of 60 percent immunity is required. If the disease spreads more easily than is commonly believed, this number may be even higher. On the contrary, with a large spread in the risk of infection, this figure may decrease.
All estimates of population immunity are based on the fact that the infection protects people from re-illness. There is convincing evidence that immunity is formed to the coronavirus, but whether it is always how strong and for how long is unclear.
Dr. Mina of Harvard suggests considering group immunity a kind of response fire, which slows down the spread of the disease.
He says that the patient, entering the room to the healthy, can infect two to three people.
“On the other hand, if three out of four already have immunity, on average one person becomes infected or even less,” he explains. This person, in turn, will also infect fewer people. Thus, the likelihood of a major outbreak is reduced.
But even with collective immunity, some people still get sick. “Your personal risk in contact with the patient does not change,” says Gypsyamber D’Souza, professor of epidemiology at Johns Hopkins University. “But the risk of contact falls.”
Diseases like measles and chickenpox, which once all children had, have now disappeared in the United States – vaccines have helped develop sufficient population immunity to control outbreaks.
We do not have a vaccine against coronavirus, therefore, on the way to population immunity without a new, more effective treatment, there will be more patients – and more deaths.
Based on the fact that population immunity occurs at the level of 60%, it turns out that New York still has two-thirds of the way. And the mortality rate so far is 250 per 100,000 New Yorkers. Millions of city dwellers can still become infected, and tens of thousands can die.
“Does anyone undertake to advise others what New York went through?” Says Natalie Dean, associate professor of biostatistics at the University of Florida. “Now many people are talking about“ controlled infection ”among young people. But counting on control is presumptuous. It’s very difficult to manage the infection.”
The virus affects populations unevenly, low-income communities and ethnic minorities have been hit harder. Antibody testing showed that in some areas of the Bronx and Brooklyn, the incidence rate is twice as high as in New York as a whole, said state governor Andrew Cuomo on Thursday. These areas are already approaching the threshold of collective immunity, in which new outbreaks are becoming less likely. But since they are not isolated from the rest of the city, where immunity is much lower, residents are still at risk.
In other cities, the proportion of people with antibodies, judging by serological studies, is much lower. The quality of these studies varies somewhat – either the samples were not completely random, or the tests were not accurate enough. However, a number of studies indicate that in most places there should be at least ten times more cases (and, therefore, deaths too) – and only then will it be possible to reach the point where new outbreaks can be excluded.
Serological studies also help scientists establish the lethality of the virus – how dangerous it is. So far, all estimates of mortality are approximate. To accurately calculate them, it is important to know how many people in one place or another died from the virus and how many were infected. Official incidence rates are based on test results and do not always reflect the true extent of infection. The true outbreak is detected by serology.
In New York, where by May 2, according to antibody testing, up to 20% of residents were infected, mortality was about 1% – more than 18 thousand people died.
For comparison, the mortality rate from influenza is estimated at 0.1-0.2%. But counting seasonal flu cases is not as accurate as serological tests. In addition, the number of infected people is often underestimated, and the number of deaths – on the contrary, is overestimated.
But even if the mortality rate is exactly the same, covid-19 as a disease is much more dangerous than the flu. The risk of getting sick and dying as the epidemic spreads is much higher.
Each season, about half the population is at risk of getting the flu. Many already have some kind of immunity – either they already had a similar strain of flu, or they did the right vaccination, which coincided with the strain of this year.
This share is not enough for population immunity – and the flu comes every year. But the population has the advantage of partial immunity: in a normal year, only a part of adults are at risk of getting sick, and the spread rate is lower. It turns out that the risk of death is also reduced.
Covid-19, unlike the flu, is a completely new disease. Until this year, no one in the world had any immunity to him. This means that even with the same mortality rate, covid-19 threatens to kill more people. One percent of a large number of cases is higher than a similar percentage of a smaller number.
“Not all 328 million Americans are at risk with the onset of the flu season every fall,” said Andrew Noymer, associate professor of epidemiology at the University of California, Irvine. “But just as much is at risk when a new infection appears.”
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