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These tests, which measure antibodies in the blood, are being used in studies in the US. USA And the rest of the world, they are crucial to understanding Covid-19 and the virus that causes it. As they are implemented, they can tell researchers and government leaders not only how many people are sick, but also how many have been found with the virus. That, in turn, may finally give you a firmer idea of how deadly the virus is and how many people potentially have some level of immunity.
“We can’t see the virus. We can trace it, its traces on people. This is our best way to do that,” said Eric Topol, director of the Scripps Research Translation Institute. “We need to use this in conjunction with other means to try to restore some relative normality. ”
Several studies are already underway. So far, early research suggests that there are a significant number of people who get Covid-19 and show no symptoms. But there are not enough to create a widespread “collective immunity” that builds a society-wide wall against infection and makes the virus go extinct.
“We are not close to collective immunity,” Topol said. “An order of magnitude of distance, at least.”
Tests look for antibodies in the blood, the immune system’s often long-lasting response to infection, rather than detecting the virus itself. The tests are usually done with drops of blood from a finger or an extraction from a vein.
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But, like diagnostic tests that use a nose or throat swab to check currently infected patients, blood antibody tests are proving to be a complex endeavor that is affected by many of the same problems as well. as for new ones.
A Stanford University study published online the Friday before the peer review found that more than twice as many people were infected with Covid-19 than current counts suggest, a number that would indicate that it is more widespread and less deadly than previously understood. This would mean that Santa Clara County in California, which has had more than 1,800 positive cases, identified only one in 50 to 85 people who actually have Covid-19.
The study quickly generated criticism from experts.
He used Facebook ads to search for volunteers, who experts say might be more likely to be interested in the test because they had symptoms, compared to a random sample from the population. Some also questioned the accuracy of the test itself.
“They assumed a very, very high specificity,” said Natalie Dean, biostatistics at the University of Florida, using the term that indicates the rate at which false positives occur. “But the reality is that we really don’t know. They didn’t explain the uncertainty in that. ”
Dean said weighing the results to better represent the demographics of people who didn’t volunteer for the study also seemed to make it appear that more people were infected.
“The results change a lot depending on the assumptions you make,” said Dean. “I think it is valuable to get a response very quickly, even if it is not exactly correct. As long as it takes us to a ballpark. ”
The authors acknowledged in the paper that there are problems with the precision of the test, as well as other limitations of the study.
“No study, as well as it is, can give the definitive answer alone,” said John Ioannidis, a professor of medicine and epidemiology at Stanford who participated in the study, earlier this month. “But in the end we have data, real data, because until now we have relied mainly on speculation.”
More than a week later, on April 30, the authors responded with an updated version of the study that more clearly presented the study’s limitations and included more data.
In a follow-up interview, Ioannidis said that while the new results were “very similar,” the authors decided to present a simpler and more conservative estimate, suggesting that 2.8% of the population had been exposed to the virus when evaluating the population for taken into account for the diversity of the county.
In any case, Ioannidis said, he believed the number was too conservative. “Science is a continuous process,” he said.
Shortly after the review was published, Topol tweeted that he believed the study was still to blame for most of its initial flaws.
Changing rates
In Los Angeles County, a collaborative study between the Department of Public Health and the University of Southern California estimated that approximately 4.1% of the county’s adult population has antibodies to the virus, or between 2.8% and 5.6% when considering possible errors. According to the researchers, that estimate is 28 to 55 times higher than the 7,994 confirmed cases at the time of the study. The researchers performed a rapid antibody test on a representative sample of the county population at six direct access sites.
Both California numbers show a much higher infection rate than other similar efforts. In China, the Zhongnan Hospital in Wuhan, for example, found that among 3,600 of its employees, a group particularly at risk of contracting the virus, 2.4% had developed antibodies, doctors there at a news conference earlier in the day said. this month.
Similar studies have produced very different rates, adding to the ongoing debate about the spread of the virus. A much smaller one in the Boston suburb of Chelsea found that of 200 randomly sampled residents where they were detained on the street and asked to give a few drops of blood, 64 had antibodies. The study was conducted by physicians at Massachusetts General Hospital.
John Iafrate, a pathologist at Harvard University and the study’s lead investigator, said the high numbers may be caused by high levels of community spread in Chelsea’s dense living conditions, as well as challenges socioeconomic.
“The good news is that most people have a mild illness,” he said. “We don’t know at this point what percentage of these antibody-positive people still carry viruses, but a fair estimate is likely to be 30-50%.”
The Centers for Disease Control and Prevention has estimated that 25% of people may be asymptomatic for the disease. The United States has confirmed more than 760,000 known cases of Covid-19, but that number is believed to be a low count.
Read more: Monitoring the spread of the coronavirus outbreak in the US USA
In the absence of an authoritative study, several ambitious antibody testing efforts have recently started. The US National Institutes of Health. USA They announced that they would assess the presence of antibodies in 10,000 healthy volunteers. New York, the state most affected by the virus, has passed an antibody test that is moving rapidly to increase its scale.
Several manufacturers have announced tests that could not only assess the spread of the disease, but also identify potentially immune individuals who could return to work, reopen schools, or help demonstrate whether future vaccines are working. Abbott Laboratories has said it will ship 4 million of its new antibody tests this month, with the goal of manufacturing 20 million a month by June.
FDA oversight
Due to the desire to bring more tests to market, the US Food and Drug Administration. USA You have relaxed the usual evaluation criteria for them. But not all tests have worked perfectly. The FDA has allowed dozens of tests to hit the market without the usual background investigation. There is evidence that there is poor performance: The agency issued a warning last week urging awareness that not all of these tests have been passed and that healthcare providers must “be aware of their limitations.” Only four tests have received official emergency authorization from the agency.
“The technology behind antibody testing is fundamentally different and generally more difficult to correct,” Anna Petherick, a public policy expert at the University of Oxford, recently wrote in The Lancet.
The development of antibody tests requires more knowledge of the structure of a specific virus than a diagnostic test. To perform the tests, the researchers produce sections of the virus’s protein to which the human immune system responds. Different tests verify the presence of different antibodies, but these antibodies can vary from person to person. And not all are the type of antibodies that indicate potential immunity. There is also concern that tests may detect antibodies to other coronavirus strains that cause different and milder diseases, such as a common cold. And even with the correct test, results can vary significantly from region to region.
“Every population at every moment is different,” said Marc Lipsitch, an epidemiologist at Harvard University who criticized the Stanford study. “And it is really difficult to compare between populations.”
But, Lipsitch said, even imperfect studies add to our knowledge of a virus that until a few months ago was completely unknown. The image may be blurry, but it is starting to focus.
“We have a feeling that perhaps the prevalence of infection is much higher than we thought,” he said. “This is now an estimate of how much bigger. But that estimate is pretty uncertain. ”
