Herd immunity is achieved when enough people become immune to a virus to stop its spread.
Around 70% to 90% of a population needs to be immune to protect the uninfected.
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“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.
“This cannot be achieved without accepting the collateral damage of many deaths in the susceptible population and overburdening of health systems.”
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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.
Prof Danny Altmann, British Society for Immunology spokesperson and Professor of Immunology at Imperial College London, described the study as “sobering”.
“Findings such as this reinforce the idea that faced with a lethal infection that induces rather short-lived immunity, the challenge is to identify the best vaccine strategies able to overcome these problems and stimulate a large, sustained, optimal, immune response in the way the virus failed to do,” Prof Altmann said.
