9.9% percent of the Spanish population has been infected with COVID-19 during the first eleven months of 2020 and has developed antibodies to the infection. It is one of every ten citizens, around 4.7 million, although there are currently 1,751,884 diagnosed with notification to the Ministry of Health. It is extracted from the statistical results of the fourth wave of the ENE-COVID seroprevalence study, presented by its directors Raquel Yotti (Carlos III Health Institute, ISCIII) and Marina Pollán (National Epidemiology Center, CNE) and which has been prepared between November 16 and 29 with rapid tests. They are still preliminary and in a few weeks more definitive results will be obtained, “it is a first communication but it is useful for public health purposes”, Yotti has specified, and they have also detected “good concordance” between the rapid test results and those that are have done with blood for ELISA tests, more accurate.
Raquel Yotti: “With 5% of the infected population we had the system surpassed and thousands of deaths; not confining would have had unaffordable costs”
These are figures that are very far from the so-called herd or group immunity – so many people immunized that there is a natural barrier against the virus – which for COVID-19 would be at least 60%. In the first part of the study, which consisted of three waves until the final conclusion, it was learned that 5.2% of citizens had developed antibodies to SARS-CoV-2. That was in July. The percentage has climbed to 9.9% during the second wave of the pandemic. It corresponds to the forecasts made by Health, the promoter of the project: they estimated that the current figure would be between 8 and 10%. In Cuenca, Soria and Madrid it exceeds 18%.
The Ministry study was already a pioneer in Europe in the spring. Its scientific rigor was recognized with a publication in The Lancet. The research allows to get a real idea of how COVID-19 has hit in Spain and also of the diagnostic capacity. The first seroprevalence study revealed that only 10% of those who had been through those months had confirmed COVD-19 at that time. Now, those responsible for the study conclude that it is detected at 60%.
It is made through a sample selected by the National Institute of Statistics (INE) of about 60,000 citizens, representative of all Spanish society. The management has been coordinated by the ISCIII, through the autonomous communities and Primary Care professionals. The citizens analyzed in July are the same as now in November, thus taking into account the number of people infected in the first wave of the pandemic and in the second. Also those who have passed the disease and initially developed antibodies but at some point lost them. The Minister of Health, Salvador Illa, acknowledged that, although the participation had been very positive, in this fourth part of the study it had cost a little more to contact the participants and obtain a ‘yes’.
Slightly more than 50,000 people participated, less than in the first three rounds but much more than in any other similar study carried out in our country before. They have been “from babies to nonagenarians,” Yotti said. 15% have undergone blood serological tests, more accurate than the rapid ones, and will be available in a few weeks.