In a nationwide population-based seroprevalence study, scientists tested for antibodies and interviewed more than 51.4 Spanish residents in November. Participants were selected at random from municipal lists of households in all regions of the country.
Based on the data obtained, scientists were able to calculate the seroprevalence range – the number of people in the population with a positive test for a particular infection. The results of the study showed that by November about 10% of the population of Spain, or 4.7 million people, had faced the virus.
“Every tenth person living in Spain has been infected with the coronavirus. Half of the people fell ill during the first wave of spring, another half in the fall, ”said Raquel Yotti, director of the Carlos III Institute of Health.
Scientists at the Carlos III Health Institute conducted the first population-based antibody study in May, and at that time it was the largest analysis of its kind in the world. The analysis included data from over 61 thousand people who answered questions about their health and were tested for antibodies. The data obtained actually put an end to the faint hope of achieving herd immunity through the maximum number of infected. Despite the fact that Spain was one of the most affected countries in the first wave of COVID-19, only 5.2% of the population had IgG antibodies.
Moreover, the rates were higher (7-10%) in “hot spots” such as Madrid and Barcelona, while in the coastal regions, which were less affected by the epidemic, the number of cases was significantly lower.
“In light of these results, any proposed approach to achieve herd immunity through natural infection is not only highly unethical, but also unattainable,” the authors wrote. Scientists emphasize that at least 90% of the Spanish population is still exposed to the pathogen, while at least 60% of those who have been ill or who received the vaccine are needed to acquire herd immunity.