Lowest number of Covid-19 infections

The study began on April 27 in more than 36,000 homes to measure the level of immunity of residents in Spain against the virus and the third round results show figures very similar to those of the two rounds.

The percentage of people who tested positive for Covid-19 in the Balearic Islands fell from 1.8% in the first round between April 27 and May 11 to 1.5% in the second round from May 18 to June 1 and 1.4% in the third, from June 8 to 22.

In the last round, involving 1,280 households in the Islands, the resulting 1.4% is the lowest percentage of all the Autonomous Communities, followed by 1.6% in Murcia.

At National level, both the percentage of the population with antibodies and the geographical distribution have remained very similar to the previous wave at 5.2%. Between the first and second round of the study 7% of the participants had detectable Covid-19 antibodies and 14% in the third round. According to the Director of the National Centre for Epidemiology, Dr Marina Pollán, not being able to detect the antibodies does not mean that people are not immunologically protected.

She explained that the "loss" of antibodies was more frequent in people who had not had any symptoms, which was 11% between rounds 1 and 2; 0.5% in participants with positive PCR results and 2.6% amongst those who experienced a sudden loss of smell or taste.

The results of the study have also shown an overall rate of seroconversion, i.e., people who did not have antibodies in the first wave developed them during the study by having contact with the virus, of 0.9% between the first and second round and 0.7% between the second and third round. The Balearic Islands were 0.6% in both cases.

According to Dr Pollán, this reflects the low appearance of new infections after confinement.

Researchers trying to define what a "possible covid case" may be are looking to people with three or more symptoms or those who experienced loss of smell and taste.

These possible cases decreased from 4% in round one to 0.4% in round two due to the lockdown, then rose slightly in round three to 1.1%.

“This data shows that we are far from achieving herd immunity and it would be very unethical to expose the population to the virus to achieve it,” says Dr Pollán, who underlined the importance of preventive measures such as wearing face masks.

The presentation of the final conclusions of the Seroprevalence study coincides with the publication of an article in 'The Lancet' which says the highest prevalence of antibodies to Covid-19 occurred in Healthcare Personnel and Health Workers at 10% followed by in Residences and Social and Health Centres at 7.7%, which is much higher than the average of the population.

Data from the third round confirmed, once again, the existence of an important geographical variability in the percentage of seroprevalence. Ceuta, Murcia, Asturias, Galicia, the Balearic Islands and the Canary Islands have prevalences less than or close to 2%, whereas Castilla-La Mancha and Madrid are 10% or more, places with more than 100,000 inhabitants are 6% and Municipalities with a lower population are 4%.

A total of 68,296 people participated in the Seroprevalence study and 54,858 did so in all three rounds, representing an adherence of almost 90%.

91% of participants provided at least one blood sample for analysis; 186,908 rapid tests were performed, plus 9,755 in the Island-specific study and 165,176 blood samples were collected, plus an additional 9,130 ​​in the island-specific study.

Faustino Blanco, Secretary General of Health, thanked the Healthcare workers for their dedication throughout the crisis and said that strengthening Primary Care is very important.

He also spoke about the coronavirus outbreaks in Lleida and Lugo, saying the virus is still there and that it’s very important to be very cautious, track down any new outbreaks and act accordingly.

"Communities have made important decisions. We are active observers of what is happening, but it is the Communities that must make the decisions regarding containment,” said Blanco, who insisted that security measures should not be abandoned.