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Antibody test shows 5% of Spaniards or 2.3 million have contracted the coronavirus

This is not the road to herd immunity

In Spain, after a long battle, a quarter of a million people have tested positive to coronavirus and 27,000 have died.

But Spanish authorities have now done the largest antibody test I am aware of, and it was at least somewhat randomized.  As many as 70,000 people have been blood tested and it was discovered that 5% had antibodies to Coronavirus. That would mean there were about 2.3 million cases of Covid-WuFlu across all of Spain, which is ten times as many cases as officially counted. But it also means 95% of Spaniards are at risk of catching it, and without a lockdown the virus would still spread very quickly. The death rate works out to be about 1.1% of total infections. But there were excess deaths in Spain — above and beyond the normal, and above the known Covid Cases — so that suggests the real death rate is more like 1.3%. Not fun.

That’s possibly why Spain is heading towards zero cases. The combination of infectiousness and the fairly significant death rate means Coronavirus is a hard virus to live with. Even a low level of running virus could fire up in a couple of weeks to 5,000 cases a day.

One third were asymptomatic. Good for them. Another number worth knowing.


Daily new cases in Spain. Worldmeters.

 Antibody study shows just 5% of Spaniards have contracted the coronavirus

Bordja Andrino, Daniele Grasso, kiko llaneras, Elena Sevillano, El Pais

  • 90% weren’t detected (because Spain isn’t doing enough tests).
  • One out of every three people who tested positive for antibodies was asymptomatic and did not realize they had contracted the virus.
  • 43% lost their sense of smell.

Only 5% of Spaniards have been infected with the coronavirus, according to the preliminary results of a study by the Carlos III public health institute, which took blood samples from nearly 70,000 participants.

The Spanish overall figure of 5% is in line with studies in other European countries that showed a prevalence of 4% to 5%, far below the rate that would provide the population with so-called herd immunity, and which experts place at 60% at the very least.

If the percentage of infected people who eventually die is around 1.1%, as the study suggests, the cost in human lives of herd immunity would be between 200,000 and 300,000, making the method unacceptable.

“Five percent is the equivalent of 2,350,000 cases. If there were around 27,100 deaths, that means that the fatality rate is between 1 and 1.2%,” explains Jesús Molina Cabrillana, an epidemiologist at the Spanish Society of Preventive Medicine, Public Health and Hygiene (Sempsph).

That is in the higher range of the best available estimates from other countries, which talk about 0.5% to 1% of deaths among people who were infected with the coronavirus, known as the infection fatality rate or IFR. In Spain, if we add another 5,900 suspicious but untested cases to the total number of infections, the fatality rate grows to 1.3%.

It’s good that 36,000 households were selected at random, but since 70,000 tests were done this means probably whole households were tested. So it is possible that the study overrepresents families and young people demographically. It may also overrepresent infections since household members are more likely to spread an infection. On the other hand, the test won’t pick up active new infections, so it will  underestimate the infections as well. There is a lag of a week before some of the antibodies form. In the wash, this might be as good as it gets as an estimate.

In Spain, herd immunity might cost 200-300,000 lives.


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