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Only 5% of the Spanish Population Found To Have Antibodies to SARS-CoV-2

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The ENE-COVID national seroprevalence study concludes that 5% of the Spanish population has antibodies. This percentage has hardly changed in the three waves of which the study consists: in the first it was estimated at 5% and in the second and third it was 5.2%, results that confirm that, despite the great impact of the pandemic in Spain, the figures are not high, which rules out the goal of group immunity in the short term.

The director of the National Center for Epidemiology and scientific director of the study, Marina Pollán; the director of the ISCIII, Raquel Yotti, and the secretary general of the Ministry of Health, Faustino Blanco, presented the results this Monday morning.

The presentation of the final results coincides with the publication today of a scientific article in the magazine 'The Lancet' , a publication recognized as one of the most prestigious scientific publications in the world and the second with the greatest impact in the field of Medicine. 

One of the issues analyzed in the study, carried out over two months, is the evolution of the antibodies, which was one of the objectives. An overall seroconversion rate (people who did not have antibodies in the first wave and who developed them throughout the study by having contact with the virus) of 0.9% between round 1 and round 2 has been observed, a somewhat lower percentage (0.7%) between round 2 and round 3. These figures reflect the low appearance of new infections after confinement.

On the other hand, seronegativization has also been observed, that is, the absence of detectable IgG antibodies in people who previously had them, being globally 7.1% between round 1 and round 2, and approximately 14% when analyzing The entire period of the study, although this last data requires confirmation. Antibody "loss" was more frequent in people who had no symptoms (11.0% between rounds 1 and 2, with more accurate information) and much less frequent in participants with positive PCR (0.5 %) and in those who described sudden loss of smell or taste (2.6%).

The map of participants with COVID-19 symptoms (people with three or more symptoms or with sudden loss of smell) in the last two weeks of the study gives an idea of ​​the most recent evolution of the epidemic. While the percentage of symptomatic patients has decreased substantially between the first and second round, a slight increase has been observed in the last round, which could be the result of the greater mobility of the population after the period of confinement. It is possible that a percentage of these patients may be cases of COVID-19 in the early phase of the disease. The monitoring of the participants may allow answering these questions. 

The authors consider that the results obtained in Spain, a country with an intense epidemic wave in which seroprevalence figures are low, reflect the difficulty of obtaining herd immunity in the short term. In this sense, the comment that accompanies the article in "The Lancet" by researchers from reference centers in Geneva (Drs Isabella Eckerle & Dr. Benjamin Meyer) points out that "it would be unethical to subject the population and the health system to increased pressure to achieve this group immunity. "

In short, these results, together with the presence of a substantial percentage of asymptomatic infections, reinforce the need to maintain public health recommendations for social distancing, use of masks, and hand washing.

Geographic variability

As indicated in said publication, and as it has already been carried out in the dissemination of preliminary data from the first waves, there is considerable geographic variability in the percentage of seroprevalence. Some provinces stand at 2-3%, while others exceed 10%, registering the highest percentages in the central part of the peninsula. The percentage is also higher in population centers with more than 100,000 inhabitants compared to municipalities with a smaller population (6% and 4%, respectively).

There are no differences between men and women and, with regard to age, the prevalence of IgG anti SARS-CoV-2 antibodies is slightly lower in children and adolescents (around 3.5%), with little variation in adults. The article published in 'The Lancet' also highlights the highest prevalence of antibodies in healthcare personnel (10%) and among workers in nursing homes and social healthcare centers (7.7%).

In the presentation of the final results of the study it has been confirmed that between 74% and 89% of the participants who reported having had a positive PCR at least two weeks before the study, IgG antibodies against the coronavirus are detected. Among people who report having symptoms compatible with the disease, seroprevalence increases with the number of symptoms and is particularly high in people who report sudden loss of smell and / or taste (40% -41%). Finally, it is confirmed that around 2.5% and 2.8% of the participants who did not report any symptoms presented IgG antibodies, which reinforces the existence of asymptomatic infections. 

Participants who reported having had contact with a confirmed COVID-19 case, or with a person with compatible symptoms, had a higher prevalence of antibodies than the general population. The prevalence in people who have lived with a confirmed COVID-19 patient stands out, which is between 27 and 31% in the different rounds. Those living with people with symptoms compatible with the disease also had a higher than average seroprevalence (15%). In people who report having had contact with a confirmed case outside the home, seroprevalence ranges from 10% to 15% in the different rounds.

68,296 participants

The three rounds of the study, promoted by the Ministry of Health and the Carlos III Health Institute, under the Ministry of Science and Innovation, and in which the health systems of all the autonomous communities and the cities of Ceuta and Melilla have collaborated they have been developed between April 27 and May 11; from May 18 to June 1, and from June 8 to 22.

It has included a total of 68,296 participants, of which 54,858 have participated in the three rounds, representing an adherence of almost 90%. Additionally, 91% of participants have provided at least one blood sample for analysis.

In total, 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).

Prevalence of SARS-CoV-2 in Spain (ENE-COVID): a nationwide, population-based seroepidemiological study. Marina Pollán et al. The Lancet, July 06, 2020, DOI:https://doi.org/10.1016/S0140-6736(20)31483-5.

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