From Sardinia to Trentino Alto Adige they ask for an immunity license for tourists. But does it make sense to do serological tests to visitors to find out if they developed Covid-19 immunity?
I have been saying this for some time and the World Health Organization has also supported it: these tests for the detection of antibodies for Sars-CoV 2 are a valuable tool for assessing the prevalence and spread of the virus and in some clinical conditions, but they do not give a Immunity license To date, we still do not know whether the presence of a certain amount of antibodies is the indicator of an immune response that ensures protection against infection.
Are circulating serological tests reliable?
The State and the Lombardy Region have chosen two valid tests in my opinion. Remember that for serological information on infectious diseases, high levels of specificity and sensitivity (over 97%) are required to avoid false positives and false negatives as much as possible. A hundred tests are on the market today, but many, perhaps the majority, have not been rigorously validated. The British government bought and threw away 35 million that proved unreliable. Regardless of the quality of the test, a person with the presumption of being immune can be induced to decide not to use the mask or not to respect social distancing: instead he could get sick and still carry the virus around.
Why is there still no evidence today on the effectiveness of immunity given by antibodies?
This virus has not studied immunology books and behaves differently than we are used to seeing. In the classical immune response, the IgM class antibodies first arrive and then the IgG class antibodies, which are generally neutralizing. But the new coronavirus follows different paths, sometimes the two immunoglobulins appear together or reversed. And when there are IgG antibodies it is possible that the virus is still present and for this you need the buffer to exclude it.
So who healed from Covid-19 isn’t forever?
For those who have really developed the disease we can reasonably think that for a certain period they will remain protected by Sars-CoV-2. Sars gave healers 2-3 years of immunity and this virus was related to him. The problem that the vast majority of people who meet Covid-19 either do not get sick or do so in a mild way: in this case we do not know whether the induced immune response, of which the presence of antibodies is a spy, is really protective or if these people risk a new infection.
What are the scenarios after a serological test?
Three things can happen: the negative serological test, but in reality the subject may have the virus because in this infection the immune response can appear up to 15 days-20 days after exposure. So this person could actually be contagious without knowing it. If the serological test is positive, there are two options: the person has encountered the virus and his immune system has eliminated it or, despite having antibodies, the virus still present, the battle still going on and this can only be discovered by the swab.
With so many uncertainties, what are these tests for?
They are useful for epidemiological investigations such as the one we concluded in Humanitas and made available to the scientific community, the first on a large scale in Italy, led by Professor Maria Rescigno. We tested 3985 among doctors, nurses, administrative staff also in smart working, researchers, in the various Humanitas structures on the Lombard territory. it emerged that 11-13% of the staff came into contact with the coronavirus, without substantial differences between the categories: the health workers, potentially exposed, compared to the rest of the population. It emerges that the hospital, if well protected, can be a safe place for patients and those who work, for this reason I invite the 10 million Italians who have different diseases such as a tumor to return to the hospital for treatment. The data also show that the prevalence of positive for antibodies among the staff of the various structures is in line with the situation of the territory they belong to: from 3% of Humanitas Medical Care of Varese to 35- 43% of Humanitas in Bergamo, the most hit in Italy.
These days we are talking about attenuated virus, what do you think?
In the database there are five thousand genetic sequences and none indicate that the virus has attenuated. We will think about it when someone brings evidence in authoritative scientific journals. It is true that patients are much less serious, but the reasons can be many: past clinical experience, we have learned about the disease; the virus initially affected the weakest people, many of whom didn’t make it; today we behave better and in this way even the most fragile are more protected; finally the diseases caused by respiratory viruses subside with spring and summer because we are more outdoors and at home we keep the windows open and the amount of exposure to the virus changes. A study funded by the Cariplo Foundation will be published shortly, which sequenced 350 viral strains in Lombardy. We wait to understand what we will say.
Alberto Mantovani, 71, an internationally renowned immunologist, replied. the scientific director of Humanitas of Rozzano, Emeritus Professor at Humanitas University
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