The final round of a major Spanish study has shown that just 5.2 per cent of people have developed antibodies to Covid-19, far below the numbers needed for herd immunity.
Spanish scientists said the results – the third and final set of findings from a study of 68,000 people – showed that Spain was a still some way from herd immunity, and any attempts to reach it naturally would "unethical".
Presenting the results, the director of Spain's National Centre of Epidemiology, Dr Marina Pollán said: “Spain is a long way from reaching so-called herd immunity, and it would be very unethical to expose the population to the coronavirus in an indiscriminate way."
The study is the largest of its kind in Europe. The results were also published in the respected medical journal, The Lancet, which said the findings showed that attaining herd immunity was impossible without an unacceptable level of death and suffering as health systems collapse.
In the conclusions to its peer review of the first round of the Spanish study, carried out from late April through to early May, The Lancet said that the low Covid-19 prevalence even in a badly-affected country such as Spain meant that herd immunity “cannot be achieved without accepting the collateral damage of many deaths in the susceptible population and overburdening of health systems”.
It said that this meant that social distancing and 'track and trace' efforts would continue to be "imperative" in controlling the pandemic. The first round of the Spanish study had showed that just over five per cent of the population showing antibodies for Covid-19.
It also showed a mortality rate of between 1.1 and 1.5 per cent, depending on whether officially confirmed fatalities due to Covid, or all suspected and known cases, were counted. Of those who tested positive in the survey, 26 per cent had not noticed any symptoms.
The three-phase study involving many repeat participants also showed how antibodies quickly stopped showing up in many cases, with 14 per cent of those who tested positive for antibodies in the first wave coming out negative two months later.
“Not being able to detect antibodies does not mean that these people are not immunologically protected,” said Dr Pollán, explaining that people can also have cellular immunity, which has yet to be studied closely during the Covid-19 pandemic.
Some experts have suggested that T-cells, a type of white blood cell that helps the immune system fight off viruses, may have as important a role to play as antibodies in taking on the virus, although more research is needed. Only in five of Spain’s 50 provinces the prevalence was found to be above 10 per cent, including Madrid with 11.7 per cent.
Spain’s official death toll from Covid-19 stands at 28,385, but the real number is thought to be considerably higher, and the country’s excess death figure from the beginning of March to mid-May is close to 43,000.
The prevalence study was carried out to determine how many people in Spain have developed antibodies after exposure to the virus.
The eight-week study was conducted by the Carlos III public health institute, which took blood samples from close to 70,000 participants.