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The Ministry of Health has released the results of the third and last wave of the seroprevalence study showing that the percentage of people who have been infected with SARS-CoV-2 remains stable at around 5% ( 5.2% specifically in the third wave compared to 5% in the previous waves ). "This shows that if a country as punished as Spain has those figures, herd immunity is very difficult to achieve," said Marina Pollán, director of the National Center for Epidemiology in the presentation of the latest wave of the study.

The seroprevalence study, named ENE-Covid, has been led by the Carlos III Health Institute, in collaboration with the National Institute of Statistics, and has been carried out in three waves separated by 21 days, in which It has recruited just over 68,000 people from 36,000 households and has both national and provincial representation.

5.2% of Spaniards with antibodies

The results of this third wave, which have been published this Monday in the scientific journal Lancet, have shown that although 5.2% of Spaniards show antibodies, up to 14% have shown seronegativization . In other words, 14% of Spaniards who tested positive for IgG antibodies in the first wave of the study, however, tested negative in the third wave.

Specifically, between the first wave of the study and the second (there is a 21-day difference between each round) 7.1% of people who had tested positive turned negative. The new data shows that they are now 14% between the first and the third round. According to the study, this loss of antibodies is more common in people who had no symptoms (it rises from 7% to 11% in this case between the first and second round of the study) than among those who did show any symptoms and much lower among people with a positive CRP (0.5%) or in those who lost their smell or taste (2.6% seronegativization).

Loss of immunity or lack of sensitivity of the tests?

Pollán explained in this regard that this absence of antibodies in the tests, this seronegativization, does not imply by itself that these people have lost their immunity against the coronavirus and has pointed in part to a possible lack of detection of the antibodies by the tests themselves . "You have to think that the tools we use to detect antibodies are the best there are but they are not perfect. Rapid tests are not capable of detecting 100% of the antibodies and the fact that we do not detect the antibodies does not mean that they are not present and even if they were not present as they occur in diseases like hepatitis, there may be immune memory in the cells . Cellular immunity also seems to play an important role in this disease, "he said. Pollán recalled that it is also still in question by the scientific community whether recurrences are occurring or not, whether or not people who had passed the disease re-contract it.

Although the lack of sensitivity of the tests could be the key in this "loss" of antibodies, the director of the Carlos III Health Institute, Raquel Yotti, has taken the opportunity to ask for caution from the population that has already passed the coronavirus: Throughout the entire study, we have repeated that having antibodies does not imply having total immunity and that even if it had that immunity, we do not know how long it is maintained. This is something that we still do not know. But we do know that immunity can be incomplete and that is why I also ask for caution from citizens who have passed the disease and who believe that they should not wear masks or should not respect social distance ... With these data what we see is that there is a loss of detectable antibodies that reveals this uncertainty in which we move, notwithstanding that there may be other factors [such as the lack of sensitivity of the tests] that may be affecting the data. My message is prudence for those who have past the disease: we must continue to protect ourselves, "concluded Yotti.

2.5% of those who test positive are asymptomatic

The new data from the seroprevalence study have also shown that around 10% of the toilets would have been infected , that the determining symptom seems to be the sudden loss of smell or taste (reported by 40% of people), that between 2 , 5% and 2.8% of people who test positive for IgG antibodies have no symptoms and that the differences between age and sex have been reduced.

Those with compatible symptoms grow

Furthermore, the study has given a closer picture of how the epidemic is behaving right now, asking about symptoms compatible with Covid-19. And according to these data, in the second wave 0.4% of the population reported having symptoms compatible with coronavirus (3 or more symptoms or loss of smell or taste), a percentage that has risen in this third wave to 1.1 % .

Faced with this situation, the outbreaks and confinements decreed in Lugo and Lérida, the Secretary-General for Health, Faustino Blanco, who has reappeared in public appearance after being practically absent from the outbreaks throughout the epidemic, has explained that "it is the autonomies to which it was up to make this decision "but" from the first moment we have explained that the state of alarm has ended, but the epidemic has not. "

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