Meanwhile, according to a study by the Polyclinic of Milan published in preview on “medRxiv”, Covid19 was not only circulating in Milan several weeks before the epidemic broke out on February 21, but even at the beginning of the health emergency already on 4 6 percent of the Polyclinic’s blood donors had antibodies to the virus: it means that one in 20 people had already come into contact with the coronavirus and had also developed immunity. If we wait for early April, this percentage rises to 7.1.
The study examines around 800 healthy blood donors who regularly attend the Polyclinic, between February 24 and April 8, 2020, thus following the progress of the epidemic from its official onset to full social distancing. Together with the routine analyzes, each donor was also made a serological test to look for possible antibodies against Sarsa-CoV-2, the coronavirus responsible for Covid-19. The test specifically looks for two types of antibodies: IgM, which is an indication of a recent infection, and IgG, which instead represent long-term immune memory. The test has a specificity of 98.3 percent against these antibodies and a sensitivity of 100 percent thus producing truly reliable results. From the results it would also emerge that the social distancing put in place to contain the spread would seem to have been of help above all to protect the younger ones, reducing the number of new infections.
Daniele Prati and Luca Valenti of the Department of Transfusion Medicine and Hematology of the Polyclinic of Milan curated the research together with Gianguglielmo Zehender of the University of Milan, in collaboration with several researchers also coming from the Luigi Sacco Hospital in Milan and from the Institute European Oncology. «The study – comments Valenti – was possible thanks to the blood samples stored in the Biobank of the Policlinico, a systematic collection of biological materials that is very important on many fronts, first of all that of research. The Biobank keeps all these samples in safe conditions, so that they can be recovered or analyzed in case of need, without altering their characteristics ». “During the phases of the study characterized by measures of social distancing – the researchers comment – there has been a progressive increase in this seroprevalence up to 7.1 percent” with confidence limits reaching 10.8 percent. This increase was found mainly in IgG, i.e. in older infections and therefore with an already developed immunity, rather than with IgM. Furthermore, this progressive increase in the percentage of exposed subjects was found above all in the younger ones, while the more recent infections (reported by the increase in IgM) were associated above all with the older donors.
“The purpose of this study – comments Daniele Prati, director of the Transfusion Center of the Polyclinic of Milan – was to examine the presence of Sars-CoV-2 infection in asymptomatic adults in one of the most affected Italian areas, and at the same time collect as many elements as possible to understand the risk factors and laboratory values associated with the disease. It is the first real scientific confirmation that a flood of infected people were present in the metropolitan area, even before the first cases of full-blown disease occurred. Even if it is a pre-print article, it is the first serological study of asymptomatic people that clearly tells us that we are far from herd immunity. Finally, the study reminds us that populations of blood donors can help us a lot to study diseases before they fully manifest. ”