A group of Spanish researchers has cast a considerable amount of doubt on the acclaimed strategy of herd immunity - as a way of combatting the novel coronavirus.
The study of more than 60,000 people estimates that around just 5% of the Spanish population has developed antibodies, according to the medical journal the Lancet reports BBC.
Herd immunity is achieved when enough people become infected with a virus to stop its spread.
Around 70% to 90% of a population needs to be immune to protect the uninfected.
The prevalence of Covid-19 antibodies was below 3% in coastal regions, but higher in areas of Spain with widespread outbreaks, the report said.
"Despite the high impact of Covid-19 in Spain, prevalence estimates remain low and are clearly insufficient to provide herd immunity," the study's authors said in the report.
"In this situation, social distance measures and efforts to identify and isolate new cases and their contacts are imperative for future epidemic control."
The study is thought to be the largest of its kind on the coronavirus in Europe.
There have been studies of a similar kind in China and the US and "the key finding from these representative cohorts is that most of the population appears to have remained unexposed" to the coronavirus, "even in areas with widespread virus circulation," the Lancet article said.