Those infected twice represent only 0.77% of the positives reported, but the detection of these cases is difficult
Scientific knowledge about covid-19 has advanced enormously since the start of the pandemic in March last year, but one question continues to baffle scientists: What are the chances that a person who has already passed the disease will be infected again ? The data collected indicates that the cases of patients who have been infected twice by this coronavirus are minimal, but the difficulties in detecting reinfections put the official figures in quarantine.
According to the latest update of the report ‘Covid-19 situation in Spain’, prepared by the Carlos III Institute on October 27, in Spain there have been 12,392 reinfections so far, but of them, only 1,080 (8.7%) have been confirmed. Another 1,764 (14.2%) are considered “possible” and the bulk of these notifications, 9,548 (77%) are listed as “probable”.
To understand how many infections are represented by reinfections among the total of positives, it is necessary to go back five months. The Carlos III began to publish the data on reinfections in its report of May 19. That day, the institute had 1,668 cases of people who had been infected twice, although only 80 of them were confirmed (the rest were possible or probable).
In any case, according to this document, including all cases, there have been 10,724 reinfections since May 19, which represents only 0.77% of the total positives recorded by the Ministry of Health since that date (1,380,747 ). Thus, it seems that reinfections are anecdotal within the global number of COVID-19 patients, although the difficulties in correctly registering the cases of people who have had the virus twice prompts caution.
The Carlos III Institute adds 12,392 reinfections, but only 8.7% of them are confirmed and the rest are probable or possible
What must happen for a contagion to be considered reinfection? In order to verify that a person has suffered the virus twice, it is necessary that in his first contagion PCR tests had been carried out and, in addition, the virus genome had been sequenced, a complete process that must also be repeated in the second case, in order to In this way, find out that the variant with which you have been infected the second time is different from the first (the antibodies developed for the first infection prevent the same variant from infecting twice). If the variants detected in the sequencing are different, it is understood that it is a reinfection, but if they are similar, it could be a relapse, caused by the virus having been able to remain in some reservoir, a cause that could also explain another of the great unknowns of the pandemic, the persistent covid. Two studies published in the journals ‘The Lancet’ and ‘Clinical Infectious Diseases’ suggest that people who have suffered from the disease enjoy 80.5% protection against reinfection and that it occurs in just 0.2 % of those already infected.
In addition, vaccines have introduced another distorting factor when determining whether a reinfection occurs: the antibodies they produce can be confused with those that the body has generated after a previous infection, also taking into account that those that have passed disease six months before vaccination have only received one dose.
“We have never been very clear about what happens with reinfections and now it will be even more difficult to find out, since with vaccination, it will be difficult to know if the infection is previous or from vaccines”, confirms the Catalan epidemiologist Salvador Macip, director of a laboratory at the University of Leicester and professor at the Open University of Catalonia
“What is evident is that vaccines also reduce the risk of reinfection because they prepare the immune system to offer a better response, and although they do not avoid the risk 100%, they can cause the new disease to be even milder or asymptomatic” , adds Pedro Gullón, professor of Preventive Medicine at the University of Alcalá de Henares.
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