Due to the magnitude of the sample, it is one of the most ambitious studies of these characteristics worldwide, as Ministers Illa and Duque have agreed to highlight. Designed by the Ministry of Health and the Carlos III Health Institute (ISCIII) with the collaboration of the National Statistics Institute (INE) and the Autonomous Communities, it will allow knowing how many people are or have been in contact with the virus, and know if the immunity is maintained over time.
Minister Illa has insisted that it was necessary to have this preliminary knowledge to evaluate the decisions made. In this sense, he has assured that the Government is acting in the right direction and that the confinement has worked.
For his part, Minister Duque stressed that "science feeds on data and these are going to be very important." For this reason, he has been convinced that the study will mark "a before and after for Spanish science in the fight against the pandemic."
According to the first conclusions, the prevalence of IgG anti SARS-Cov2 antibodies in the population is 5%, very similar in men and women. It is lower in infants, children, and young people, and remains fairly stable in older age groups.
Furthermore, 87% of the participants who report having had a positive PCR, present IgG antibodies. In possible suspected cases, the prevalence increases with the number of symptoms. It is particularly high, at 43%, in people who report anosmia (total loss of smell). Finally, 2.5% of the participants who did not report any symptoms presented IgG antibodies.
By autonomous communities, there is a marked geographic variability. Thus, Ceuta, Murcia, Melilla, Asturias and the Canary Islands have prevalences of less than 2%, while the Communities of Castilla-La Mancha and Madrid exceed 10%. In the provincial maps, the central grouping of provinces with prevalences equal to or close to 10% in the Madrid area stands out.
On the other hand, the map of possible suspicious cases COVID19 (people with 3 or more symptoms or with sudden loss of smell) also shows this central aggregation, with prevalences close to 20%, although equally high values are also observed in some other provinces.
These results are provisional, corresponding to the rapid tests carried out since April 27 on 60,983 people in the national sample. They do not include the other 3,234 samples taken in the specific island study, which is carried out in Fuerteventura, Lanzarote, La Gomera, El Hierro, La Palma, Formentera, Menorca, and an additional sampling in Ibiza.
The participation rate among people who have been contacted reaches 74.7%. The forecast is to reach the figure of between 60,000 and 90,000 participants when the study ends, in about six weeks.
In this first phase, telephone calls were made to 35,000 randomly chosen households throughout Spain. In parallel, participants have been taking samples at health centers and homes.
On the one hand, they have undergone a rapid test for the determination of antibodies in blood, using a finger prick. To ensure the reliability of the results and to apply the maximum methodological rigor, blood samples have been additionally obtained by venipuncture (puncture in the arm), in those participants who have given their consent.
The results presented this afternoon do not include the information from this second type of tests, which measure the antibodies by immunoassay, since the results are not available for all the Autonomous Communities.
In the following waves, it will be possible to know the evolution of the prevalence and the changes observed over time in the participants.
Finally, in her speech, Illa thanked the "invaluable collaboration" that the seventeen autonomous communities and the autonomous cities of Ceuta and Melilla are providing, through their Primary Care teams.
He also referred to the "enormous effort" of the thousands of professionals who are carrying out the study from more than 1,400 health centers or moving to the homes of citizens.