A Study concludes that only the 5% of Spanish population have antibodies

USPA NEWS - The National ENE-COVID Seroprevalence Study concludes that 5% of the Spanish population have antibodies. This percentage has hardly changed during the three waves of the study: 5% during the first, and 5.2% during the second and third. The results confirm that, despite the significant impact of the pandemic in Spain, these figures are not high and reject any possible short-term herd immunity.

Antibody trends is one of the issues examined by the two-month study and was one of the objectives. There was an overall seroconversion rate (individuals with no antibodies during the first wave who developed them during the course of the study after coming into contact with the virus) of 0.9% between round 1 and round 2 and a slightly lower percentage (0.7%) between round 2 and round 3. These figures reflect the low appearance of new infections following the lockdown.

Seronegativisation was also observed, i.e. the absence of IgG antibodies detectable in individuals who previously had them. Overall, this stood at 7.1% between round 1 and round 2, and approximately 14% when looking at the entire period of the study, although this last figure requires confirmation. The "loss" of antibodies was more frequent in individuals who had been asymptomatic (11% between round 1 and round 2, with more precise information) and much less frequent among participants with a positive PCR test (0.5%) and in those describing a sudden loss of taste or smell (2.6%).

The map of participants with COVID-19 symptoms (individuals with three or more symptoms or with a sudden loss of smell) in the last two weeks of the study provides an idea of more recent trends in the epidemic. While the percentage of symptomatic individuals fell substantially between the first and second rounds, a slight increase was seen in the last round. This could be the result of increased mobility in the population following the lockdown period. It is possible that a percentage of these patients could be COVID-19 cases in early stages of the disease. Continued monitoring of participants will enable these questions to be answered.

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

Geographic variations

As stated in the publication and in the communication of preliminary data from the first waves, there is significant geographic variations in seroprevalence percentages. Some provinces stand at 2-3% while others have over 10%, with the highest figures being recorded in the central regions of mainland Spain. This percentage is also higher in population centres with more than 100,000 inhabitants when compared with municipalities with a lower population (6% and 4%, respectively).

No differences were observed between men and women, while, in terms of age, the prevalence of IgG antibodies against SARS-CoV-2 is slightly lower in children and teenagers (around 3.5%), with insignificant variations in adults. 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 extra 9,130 in the island-specific study).