A large-scale study into Covid-19 in Spain has found that only 5% of the population has antibodies - nowhere near the levels needed to achieve herd immunity.
Spain was one of the countries hardest hit by the coronavirus pandemic with 28,385 fatalities.
Even so, only 5% of the population has antibodies that prove prior infection by the virus, according to a nationwide study of more than 60,000 people using two different tests to try to assure accuracy.
To achieve herd immunity that would protect the uninfected, around 70% to 90% of a population needs to be immune from an illness.
Data from participants - who ranged in age from infants to people in their 90s - showed some variation by region but nowhere near levels needed for herd immunity.
The prevalence of coronavirus antibodies was less than 3% in coastal regions, but more than five times higher in areas with major outbreaks.
"Despite the high impact of Covid-19 in Spain, prevalence estimates remain low and are clearly insufficient to provide herd immunity," the study authors reported in medical journal The Lancet today.
"In this situation, social distancing measures and efforts to identify and isolate new cases and their contacts are imperative for future epidemic control."