Herd immunity is not feasible to control the spread of COVID-19, according to a study thought to be the largest in Europe.
The Spanish trial involved more than 60,000 people and it is thought only 5 per cent of the country’s population has developed the coronavirus antibodies.
Herd immunity occurs when enough people become infected and so the spread is stopped. In order to protect the uninfected, between 70 to 90 per cent of the population must be immune.
The authors wrote: “Despite the high impact of COVID-19 in Spain, prevalence estimates remain low and are clearly insufficient to provide herd immunity.
“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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“In this situation, social distance measures and efforts to identify and isolate new cases and their contacts are imperative for future epidemic control.”
The findings also suggest that COVID-19 immunity could be short lived anyway, because 14 per cent of those who tested positive for the antibodies in the first test, then tested negative in the second.
Dr Raquel Yotti, director of the Carlos III Health Institute which co-led the study, said: ”Immunity can be incomplete, it can be transitory, it can last for just a short time and then disappear.
“We can’t relax, we must keep protecting ourselves and protecting others.”
Professor Danny Altmann, British Society for Immunology spokesperson and Professor of Immunology at Imperial College London, said the findings were “sobering”.
He added: “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.”
Spain was badly hit by the pandemic and so far has recorded 28,385 deaths, however the country is still struggling with regional outbreaks.