No more than five per cent of the population of France and Spain, two of the countries hardest hit by coronavirus, have contracted the disease, two new studies have found in a major blow to hopes of "herd immunity".
A mere 4.4 per cent of the French population – 2.8 million people – have been infected, according to findings by the Pasteur Institue, published in the journal Science and based on models applied to hospital and death data.
Even in the worst hit parts of France, the eastern area and the Paris region, the infection rate only reaches between nine and 10 per cent on average, the research found.
Such figures are considerably higher than the official count of cases but far too low to effectively stop the spread of the virus through group immunity.
"Around 65 per cent of the population should be immune if we want to control the pandemic by the sole means of immunity", it said.
Herd immunity refers to a situation in which enough people in a population have immunity to an infection to be able to effectively stop that disease from spreading.
The Pasteur Institute's infection rates were measured on May 11, the day France started to relax its almost two-month-long lockdown.
Strict confinement led to a drastic decline in the coronavirus reproduction rate, which went from 2.9 to 0.67 over the 55-day virtual standstill, said the researchers.
However, their findings suggest that "without a vaccine, the herd immunity alone will not be enough to avoid a second wave at the end of the lockdown. Efficient control measures must thus be upheld after May 11".
The government has said it is ready to to conduct 700,000 tests a week and send contact tracing "brigades" to contain new clusters around the country. France's overall death toll from the virus has risen to 27,074, and the total number of cases officially stands at 177,700.
A new study in Spain produced similar preliminary results, revealing that five per cent of the population has been exposed to the virus and developed antibodies.
The result means Spain will continue to plot a cautious course out of its strict lockdown measures, from which only half of the country has passed into phase one of a three-stage exit strategy stretching through June and possibly into July in the worst-hit areas such as Madrid and Barcelona.
"In principle, these results provide no basis on which to vary the plan we are working on," Salvador Illa, Spain's health minister, said on presenting the results of a survey involving more than 60,000 people from across the country, representing all ages and walks of life.
As of Wednesday, Spain had recorded just under 229,000 cases of coronavirus, with an official death toll of 27,104.
The prevalence of infection revealed by the survey means the mortality rate in Spain is 1.1 per cent, and may be closer to 1.5 per cent if suspected Covid deaths not confirmed by testing are included. Most scientific estimates had placed the mortality rate at below one per cent.
Of those who tested positive in the survey, 26 per cent had not noticed any symptoms. Of all the symptoms reported, including coughing, diarrhoea and headaches, the most prevalent among people who tested positive was the loss of smell, which appeared in 43 per cent of cases.
Among children, prevalence was three per cent among the five-to-nine age group, and just under four per cent among pre-teens and teens.
"Herd immunity is not going to be possible until there is a vaccine, unless we are prepared to accept an enormous human toll," Pere Godoy, the president of the Spanish Epidemiological Society, told the newspaper El Pais.
"The virus has proved to be very dangerous, and any policy that allows it to circulate comprises a huge risk."
Of Spain’s regions, Madrid had the highest proportion of positive tests, with 11.3 per cent of the population showing IgG antibodies.
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