Just a year ago, the medical device market saw the emergence of dozens of rapid blood tests that were supposed to detect, in a matter of minutes, whether or not a person was immune to Covid-19. These devices, which operated by taking two drops of blood from a fingertip and then depositing them on a strip, quickly proved to be of poor quality, the fault of low specificity and sensitivity making their verdict difficult to interpret.
There then remained the option of taking a blood test, then sending the sample to the laboratory for analysis. Problem: These tests, although reliable, use expensive reagents (between 3 to 10 Swiss francs per unit) and need to be carried out by trained healthcare personnel, which represents a major obstacle to carrying out studies aimed at to monitor on a large scale the prevalence of anti-SARS-CoV-2 antibodies in the population, or to follow the reaction of the immune system following the administration of a vaccine.
It is essential to have serological data if we want to understand the dynamics of an epidemic
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A study published in the journal PNAS by a team from the Federal Polytechnic School of Lausanne (EPFL), the University of Geneva (Unige) as well as the University Hospitals of Geneva (HUG) today lifts the veil on a new process making it possible to analyze more than 1000 samples at a time on a single small device, requiring only one drop of blood and using 1000 times less amounts of reagents than a standard serological test. These tests would also have a specificity of 100% (which means that the device never detected false positives, in other words antibodies in people who had never been infected with SARS-CoV-2) , and a sensitivity of 98% (or 2% false negatives, people with many antibodies that the test could not detect). These results were obtained on the basis of the analysis of 134 blood samples from people who have not previously contracted Covid-19 and 155 others who have obtained a positive PCR test in the past.
Potential savings
Concretely, this new platform consists of a network of very small tubes cut from a plastic chip called “microfluid” the size of a USB key. To perform the test, the researchers introduce individual blood samples and the reagents into the channels of this chip. If antibodies to SARS-CoV-2 are present, a molecule generates a signal that can be detected under a microscope in the form of a fluorescent glow.
In their study, the researchers also demonstrated that a small amount of blood, including dried blood, could be used, de facto eliminating the need for a blood test.
To do this, the authors tested three commercial blood collection devices and showed that it was possible to use simple, low-cost blood glucose test strips for collecting and shipping samples, which can be stored up to six days at room temperature with minimal degradation. “Performing hundreds of tests on a single platform also means that one person can perform more tests in less time, potentially saving money,” notes Sebastian Maerkl, director of the Biological Network Characterization Laboratory at the EPFL and co-author of the study, in a press release issued on May 3. If you do a rough calculation taking everything into account, including the costs of salaries and reagents, it comes down to around 0.5 Swiss francs per test, which is almost negligible. ”
Tests in schools and kindergartens
Aside from its cost, this approach would also have the advantage, according to its designers, that it could easily be carried out at home, the process consisting of performing a simple prick on the fingertip before the sample is sent to a central laboratory taking care of it, meanwhile, its analysis and the return of the results by e-mail or via a smartphone application. “This method could also be used for remote geographic regions that do not have sufficient laboratory capacity or, because of its rapid and almost painless appearance, in children,” notes Isabella Eckerle, another co-author of the study and doctor in charge of the Center for Emerging Viral Diseases at HUG. This offers the possibility of assessing prevalence rates in day care centers or kindergartens. “
And precisely: it turns out that these tests are currently used as part of the study SEROCoV-Schools, launched in March by the Population Epidemiology Unit (UEP) of the HUG. The latter aims to describe the transmission of the SARS-CoV-2 virus among children aged 2 to 6 years old and attending nurseries and schools in the canton of Geneva. “The study includes a surveillance component that will last until the end of the school year and an investigation component in the event that infections should occur in a school or nursery, details at the time Professor Silvia Stringhini, head of the UEP and member of the Covid-19 scientific task force. In this context, we systematically carry out, at the outset, an oropharyngeal PCR test as well as a serological test to all children and teachers who have agreed to participate. Then we monitor the symptoms reported over time, as well as the positive tests declared in the school population, in kindergartens as well as among educators and teachers. In the case of an infection, our goal is to identify potential clusters by testing not only students within classes, but also families of positive children, in order to better understand to what extent the youngest are vectors. infection. “
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Silvia Stringhini: “We need to test more systematically in schools”
Already particularly difficult, the process of convincing parents to let the children participate would have been even more complicated if the serological tests had required a blood test. “Having these hair tests available was particularly useful to us in the field,” adds Silvia Stringhini. As the process was experimental and we are still awaiting results, it is still a little early to know if these tools are as efficient as standard serological tests. However, it is essential to have serological data if we are to understand the dynamics of an epidemic, and more invasive methods would have been practically impossible to implement in schools. “
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