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aS News Emerged This week that the experimental vaccine against Covid-19 has been shown to be effective in late-stage clinical trials, it is hoped that epidemic days may be counted longer (see article) but, with good luck, no vaccine in those countries will begin to make a difference. It will be months before it gets its first supply, leaving the back of the queue. Meanwhile, the epidemic is raging.
To try to slow it down, many countries are starting to deploy tests, which accurately polymerase-chain-react at some cost (delivering their results faster than it does).PCR) Tests were common at the onset of the epidemic. These rapid tests will allow the potential number of infected people to be detected and isolated before the infection spreads. So the number is being increased to increase the number of people for their presence SARS–COV.-2, the virus that causes Covid-19, in settings ranging from airports to nursing homes. In Europe, indeed, they are sometimes used for blizzards throughout the neighborhood, cities and even in small countries like Slovakia. But will they change the course of the epidemic?
Small, fast, affordable
PCR Tests look for the genetic sequence of the virus in the bottom of the nose and throat. These swabs have to be processed in laboratories and as a result incoming machines take hours. They are extremely accurate. But the delays involved can make testing and trace systems difficult.
In contrast, rapid tests, which are designed to detect certain proteins SARS–COV.-2 shed when it mimics during infection. These proteins, called antigens, stimulate the immune system to make other proteins called antibodies, which continue to inactivate the virus. Antigen tests require no laboratory backup and can report results in 15-20 minutes. They work by dipping the swab into a vial containing a solution that is the antigen of the juice. A few drops of the mixture are then applied to a test strip with antibodies that identify the antigen. The test bar shows results similar to a home pregnancy test.
The speed at which these tests have been developed is impressive. According to a catalog created by the Foundation for Innovative New Diagnostics, there are now more than 70 markets in one part of the world or another.Search), A charity in Geneva that supports the World Health OrganizationWHO) With research on diagnostic tools. So far, only two of them have been approved by the Provisional (“Emergency Use”) WHO, And seven by the U.S. Federal Regulatory, Food and Drug Administration. But more approvals are expected in the coming weeks Search And other institutions complete accreditation studies that test the tests in real-life situations in which they are likely to be used.
Early antigen tests were not terribly good, but many newer tests are extremely accurate. If PCR If the test is negative, a modern antigen test on the same person will agree with that analysis more than 97% of the time, the value of which is called its specificity. The story gets complicated, though, when the viruses are really around. If one tests positive for Ema Covid-19 PCR Testing, the best antigen tests will agree in more than 90% of cases if the test is taking place in a week or so The onset of symptoms, called sensitivity. But if the antigen test is done at the beginning or end of the infection, the rate of contractions decreases, while the amount of virus in the nose and throat is significantly lower. This means that diagnoses based on antigen tests are unreliable during that period.
Fortunately, from a public-health perspective this makes no difference. The relationship between viral load and infectious disease is not fully understood, but the current thinking is that overload makes people more contagious. People with more emphasis on antigen testing are more likely to show up as positive and are therefore asked to isolate themselves, so the transmission-breaking value of new tests should not be compromised too badly.
In theory, then, all of this sounds great. But the reality is messy. Even if tested very accurately, less true money is produced than false money if the people being tested are not likely to be infected in the first place (see chart). That would be the kind of problem that arises with mass testing in places where there are no Covid-19 hotspots. For example, the UK Office for National Statistics estimates that 0.82% of people in private homes in London were infected on 28 October. If everyone in London that day was given a test that has at least “acceptable” accuracy for the quick tests determined by WHO (% 0% sensitivity and 97% specificity) The number of false-positive results will be 3 353% greater than the number of true-positive results.
Therefore, determining whether to trust the result of an incomplete rapid test – or, indeed, whether it is appropriate to use the test – depends on who is being tested, and why. A positive result is more reliable for a person with symptoms, or who is in close contact with an infected person and probably lives in an area with a high covid-19 rate. But testing is likely to be in vain when people have no clear reason for being infected. In that case the positive result will be doubtful.
Try this at home
Doctors are used to making such decisions when examining things like cancer, sexually transmitted infections, etc. They draw working guidelines on years of research and study. But things are new and changing fast for the Covid-19. To deal with this, some test developers are linking their products to “digital reparounds” such as applications that provide up-to-date data on such decision-making algorithms, local covid-19 prevalence trends and various weights. Individual risk factors taken by different risks. Some of these applications issue time-limited bar codes to negative testers, for use where proof of negative testing may be required.
For now, rapid tests are only licensed for use by medical professionals. The regulatory belt set for home tests alone is low. They must be 99% accurate and must undergo extensive utility trials to make sure people employ them properly. It would be easier if the secretion was examined saliva, which is freely accessible instead of the material found high in the nose or in the throat. Saliva acts reliably in some PCR Tests but no one has yet developed a good antigen test that uses it.
At the current pace of progress, however, this may soon change. Bruce Tromberg of the U.S. National Institutes of Health (NIH) Thinks rapid over-the-counter testing may be available in the U.S. as early as next summer. After that, rapid antigen tests are likely to be a big part of countries’ Covid-19 testing strategies. In particular, it will be used to perform at home, doctors’ surgeries and remote locations PCR Labs not available. They will help for mass testing, especially in places prone to epidemic outbreaks, such as prisons and student dormitories.
As more rapid tests are developed and their demand increases, competition and production will become relatively cheaper. Antigen tests alone are now available for as little as $ 5, but eventually the price could come close to $ 1, which is the cost of a quick test for malaria. Tests using small machines cost about -20 10-20 for each, plus a few hundred dollars for the device. a PCR Testing now costs about આશ 50, but will be cheaper for automated large-scale testing of samples that come in bulk on a mass schedule, such as samples from universities or workplaces.
Although antigen tests are cheap, some people worry that rich countries will corner the market for them until production increases enough, leaving poor places with shortages. To avoid this, the Bill and Melinda Gates Foundation, a major charity, has worked together. WHO To order 120m faster tests that will go to 133 developing countries in the next six months.
Dr. Tr ટ્રmberg, who leads a project NIH Investing in new Covid-19 testing technologies that can be rapidly increased for mass production, the pipeline will add 2.5 M tests a day by the end of this year based on 22 products that are already in production stage – will help the US increase total. 6m-7m. Worldwide, many manufacturers of Quick Covid-19 tests have stated that they have the capacity to take tens or millions of tests a year. This sounds appropriate given the fact that 400m malaria test kits are made every year. But there is expansion in the billions Terra hiding. Although new production lines can be built and existing ones can work around the clock, testing requires skilled workers, who are in limited supply.
Whether rapid tests change the course of the epidemic and eliminate the need for low-dose contraceptives until the vaccine can be made and distributed on the same scale will depend on whether what is available is used judiciously. Ultimately, such vaccines will dramatically reduce the demand for tests. But, for now, the world needs them.■
This article appeared in the Science and Technology section of the print edition under the title “Test Match”
