The results show that 95% of the Spanish population remains sensitive to the virus. Collective immunity is reached when enough people have been infected with a virus or bacteria - or vaccinated against it - to stop its circulation.
The European Center for Disease Control told CNN that Spanish research, out of a nationally representative sample of more than 61,000 participants, appears to be the largest study to date among a dozen coronavirus serological studies undertaken by countries Europeans.
It adds to the results of an antibody study involving 2766 participants in Geneva, Switzerland, published in the Lancet of June 11.
There have been similar studies in China and the United States and "the main conclusion of these representative cohorts is that most of the population appears to have remained unexposed" to Covid-19, "even in virus-circulating areas widespread, "said a Lancet. comment published with Spain's conclusions.
"In light of these results, any proposed approach to obtaining collective immunity through natural infection is not only highly unethical, but also unworkable," said Lancet review authors Isabella Eckerle, director of the Center. of Geneva for emerging viral diseases, and Benjamin Meyer. , virologist at the University of Geneva.
Doctors do not know whether having antibodies to the coronavirus means that a person cannot be infected again. It is not known how long or how well antibodies protect people against the virus.
The Spanish peer-reviewed study began in April while the nation remained strictly stranded, and was conducted by leading government research and epidemiology agencies.
"The relatively low seroprevalence observed in the context of an intense epidemic in Spain could serve as a benchmark for other countries. At present, collective immunity is difficult to achieve without accepting the collateral damage of many deaths in the sensitive population and overburdened health systems, "said the report.
The lead author of the Spanish study, Marina Pollán, who is director of the National Center for Epidemiology, told CNN: "Some experts have calculated that around 60% of seroprevalence could mean collective immunity. But we we are very far from reaching that figure. "
Spain is one of the European countries hardest hit by the coronavirus, with more than 28,000 deaths and 250,000 cases.
The Lancet published the results of the first phase of the Spanish study, conducted from April 27 to May 11, which showed a national prevalence of antibodies of 5%.
But the Madrid metropolitan area, the hardest hit in the country by Covid-19, had a prevalence of more than 10%, and the urban density of Barcelona had 7%, while many other coastal provinces had much higher rates. low.
Similarly, the prevalence of Geneva was 10.8% in the Swiss study conducted from April to early May, reported the Lancet.
"With a large majority of the naive population infected, the circulation of the virus can quickly return to its early pandemic dimensions in a second wave once the measures are lifted," wrote the authors of the Lancet comments, Eckerle and Meyer.
The results of the second phase of the study in Spain were published on June 4, showing a national prevalence of 5.2%, slightly higher than that of the first phase. The results of the third and final phase were released to the public on Monday; they showed that the national prevalence remained at 5.2%, said Pollán.
