How many asymptomatic infections are there? How far are we from “mass immunization”?

According to the World Health Organization, the cumulative number of people diagnosed with the new coronavirus worldwide has exceeded 11 million so far. However, this figure is confirmed by the number of patients tested for nucleic acid. We know that about 80 percent of patients infected with the new coronavirus have mild or no symptoms, and many of them may never have been tested for nucleic acids or know if they have ever been infected with the new coronavirus. Serological testing, which can detect the presence of antibodies against the new coronavirus in the patient, to better understand the number of people who have been infected with the new coronavirus, is important in epidemiological research and public health management.

In a paper published today in the Lancet, a leading medical journal, researchers conducted serological tests on more than 60,000 participants nationwide in Spain. The study found that about one-third of serotonin-positive participants did not exhibit symptoms associated with COVID-19. Nationwide, only 5 per cent of participants tested positive for serotonin, and in urban areas such as Madrid, where the new crown outbreak is severe, the serotonin rate was no more than 15 per cent. In their paper, the researchers said the data showed that the Spanish population was still far from meeting the criteria for herd immunity.

Detection method

The Serological Epidemiological Survey, called ENE-COVID, is a serological study covering the population of Spain as a whole, with the aim of investigating the serotonin positive proportion of the new coronavirus in the Spanish population. The study randomly selected 35,883 families based on population data and invited these family members to participate in serological tests, which resulted in 66,805 participants.

The researchers tested participants using two different serological tests, one that was 100 percent specific to IgG antibodies for the new coronavirus and 82.1 percent sensitivity, while the other, a chemical fluorescent response-based immunotest (called “immune testing”) with a specificity of 100 percent and a sensitivity of 89.7 percent. A total of 51,958 people received both instant and immunoassays.

Survey results

Serotonologist testresults showed that between 27 April and 11 May 2020, the population of Spain had a 5.0% serological positive rate (using instant testing) and used immunotests, a figure of 4.6 per cent, 3.7 per cent of participants who tested positive in both tests and 6.2 per cent of the participants who tested positive in one of the tests. In the seven provinces with the worst outbreaks in central Spain, the serotonin positive rate is between 10 and 15 per cent.

The study found no significant difference in serotonin positive rates between men and women, but instant testing showed that the seropositive rate was 1.1% in infants under one year of age and 3.1% in children aged 5-9. The proportion of serotonin-positive participants who did not report new coronary symptoms was 32.7% (immediate testing) or 28.5% (immune testing). About 90% of patients with COVID-19 who were diagnosed with positive nucleic acid tests 14 days before receiving serotonin tests were serotically positive.

Some revelations

The Lancet also published a commentary today explaining the significance of the study. In addition to the Spanish study, a serological survey of the population of Switzerland and Wuhan, China, yielded similar results, the commentary noted. A key finding of these serological surveys is that the majority of the population is still not infected with the new coronavirus, even in areas where the outbreak is so severe that it is putting a heavy strain on the health system. This means that at the population level, we are still far from reaching the level of mass immunization.

Researchers conducting the Spanish Serological Survey noted in the discussion of the paper that about one-third of people infected with the new coronavirus had no symptoms. The findings further underscore the importance of rapid detection, research and isolation of people diagnosed with newly coronavirus infectionand and those who have come into contact with them.