This rate is very similar to that of the first wave of the study, which stood at 5%. This second wave was carried out between May 18 and June 1.
Thus, more than 5% of the Spanish population has developed immunity against the virus that causes COVID-19, a slightly lower rate in men (5.01%) than in women (5.40%). In relation to age, the presence of the IgG antibody is lower in infants, children and young people, and there are moderate differences between the rest of the older population groups.
Although the national average is 5.21%, the study shows a marked geographic variability, also very similar to that observed in the first round, with prevalences equal to or close to 10% both in Madrid and in the surrounding provinces. .
In relation to the size of the municipalities, there is a slight increase in this immunity rate compared to the first wave in large cities (more than 100,000 inhabitants), which have gone from 6.4% to 6.8%.
80.5% of study participants who report having tested positive for coronavirus in a PCR diagnosis more than two weeks ago have IgG antibodies. In suspected cases, the prevalence of this antibody increases with the number of symptoms and is particularly high in people who have experienced loss of smell (40%). In the case of asymptomatic participants, 2.8% had IgG antibodies detected.
There are 0.8% of participants who, being antibody negative in the first round, have seroconverted in this second round, that is, they have been detected for the presence of IgG that they previously lacked. The cases of Ávila, Valladolid and Palencia stand out, with values close to 2%, and those of Madrid, Soria and Segovia with 1.5%.
Finally, the map of possible cases with symptoms of COVID-19 in the last two weeks shows, in general, lower prevalences than in the first round. Only the provinces of Santa Cruz de Tenerife, Granada, Madrid, Toledo and Las Palmas are around 1%. Possible cases with symptoms of COVID-19 refers to people with three or more symptoms or with sudden loss of smell.
Provisional result
People who participated in the study underwent an epidemiological survey on COVID-19, a rapid immunochromatography test and, who agreed, a blood draw to determine IgG antibodies by immunoassay.
The combination of both techniques allows to maximize the representativeness and quality of the information, so the results of these preliminary reports are provisional until the incorporation of the results obtained by immunoassay.
Immunoglobulin G (IgG) is the most abundant type of antibody in the body. It is found in blood and other fluids, and provides protection against bacterial and viral infections. Specialists can assess immunoglobulin levels in the blood to see if a person has an infection or is protected against it (they are immune to it).
Wide sample representation
The Spanish seroprevalence study is one of the studies of these characteristics worldwide with the largest sample representation.
63,564 people participated in this second round of the ENE-Covid-19 study, a figure higher than that of the first wave in which 60,983 collaborated. Furthermore, there has been a high adherence since 95% of the participants in the first wave have accepted to participate in the second.
The participation rate among eligible individuals has also improved to that of the first round with 66.5% compared to 63.7% in the previous period. If only the people who have been contacted are considered, the participation figure reaches 76.1%, two points more than in the previous round.
The objective of the ENE-Covid19 is to estimate the prevalence in Spain of SARS-Cov2 infection by studying the presence of antibodies against this virus, which causes the disease.
This study is the result of collaboration between the Ministry of Health, the Carlos III Health Institute, under the ministries of Science and Innovation and Health, and the health system of all the Autonomous Communities and the autonomous cities of Ceuta and Melilla. In addition, there is an agreement with the National Statistics Institute (INE).
The Ministry of Health has led the coordination with the CCAA and is responsible for the computer platform developed specifically for the collection of all the study information.
