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Serological study: 1.9% of Portuguese have antibodies against Covid-19

1.9% of the Portuguese population developed antibodies against Covid-19 by September of this year, according to the largest serological survey conducted so far in our country. The study – which aimed to analyse the degree of immunity of the Portuguese to SARS-CoV-2 – was carried out by the Instituto de Medicina Molecular João Lobo Antunes (iMM) and involved over 13,000 volunteers.

Although this is a low percentage, the prevalence of 1.9% HIV-positive indicates that by September at least 195,000 people had been in contact with the virus, a number well in excess of the 75,542 cases officially registered by 30 September in Portugal.

The prevalence of the infection found was associated with the first wave of the pandemic, although the survey took place between 8 September and 14 October 2020. According to the document:

“As antibody production increases from the time of infection and it may take two weeks to detect them in a blood sample by a serological test, the results refer to people who will have been infected from the beginning of the pandemic until mid-September”.

Greater immunity in cities

The estimated prevalence is higher in high population density regions: 2.5% in high population density regions compared to 1.4% in medium density regions and 1.2% in low population density regions.

Young people have more antibodies

The serological survey also shows that young people under 18 have slightly higher levels of this type of immunity to the disease – 2.2% in the underage group, compared to 2.0% among those aged 18 to 54 and 1.7% among those over 54. This difference is accentuated when age groups and population densities are crossed. In this case, seroprevalence in young people under 18 living in high population density areas is significantly higher – 3.2%.

Bruno Silva-Santos, deputy director of iMM and principal investigator of this study refers:

“The results of this study provide a picture of the first wave of OVID-19 and show that the country managed to “flatten the curve” in the first wave of the pandemic, which translates into an estimated prevalence of SARS-CoV-2 infection of only 1.9% in the population. Not surprisingly, the figures are clear to show that this prevalence increases with population density, assuming a statistically higher value in high density regions. We are still working on the data from the health questionnaires, factors associated with OVID-19 symptoms and other diseases, which will allow us to make a more complete analysis of this picture of the first wave of the pandemic. The pandemic situation today is different from the one we have portrayed in this study and therefore it is important now to follow and understand the evolution of the infection through the monitoring of a representative subgroup of these citizens”.

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