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Infectious Diseases

Updated 20 July 2020

Covid-19: An extensive study of the outbreak in Spain found most people did not develop immunity

A country-wide study has found that most of the Spanish population has not developed antibodies against the coronavirus.

  • A country-wide study showed that only 5% of Spain's population had coronavirus antibodies 
  • This means herd immunity appears unachievable in the current pandemic
  • About a third of the participants were found to be asymptomatic

You've probably heard the term "herd immunity" thrown about in arguments for and against pandemic lockdowns.

The idea is that if enough people are infected and recover from the coronavirus, they will have developed antibodies against it, which will prevent the virus from spreading to those without immunity. 

But a massive country-wide study from Spain – hard-hit in the early stages of the global outbreak – may have derailed this argument completely with its latest findings. 

READ: Your antibodies may only last a few months after recovering from the coronavirus 

Low prevalence of antibodies

Published in The Lancet and commissioned by the Spanish Ministry of Health and the Institute of Health Carlos III, just over 61 000 people in almost 36 000 households were tested for antibodies between April and May just after the country reached its peak.

Only 5% of them tested positive for Covid-19 antibodies on average, while in hotspot areas like Madrid it hovered at around 10%. Provinces along the coast had lower seroprevalence. 

In order to achieve herd immunity, you would need about 60% immunity.

Participants answered a questionnaire on their history of Covid-19-like symptoms and risk factors, received a point-of-care antibody test, and, if agreed, donated a blood sample for additional testing.

ALSO READ: Covid-19 antibody tests: Will they be reliable enough to manage the pandemic in the future?

Other findings

In 7 273 individuals with a loss of sense of smell or at least three other symptoms, only 15.3% to 19.3% had antibodies, and around a third of seropositive participants were asymptomatic.

Children also had a lower chance of having coronavirus antibodies, concurrent with evidence showing how age affects infectivity.

"Despite the high impact of Covid-19 in Spain, prevalence estimates [of antibodies] remain low and are clearly insufficient to provide herd immunity," writes the scientists.

"At present, herd immunity is difficult to achieve without accepting the collateral damage of many deaths in the susceptible population and overburdening of health systems." 

An earlier Chinese study also showed similar results, where patients retained their antibodies for only a few months after recovery, and that asymptomatic patients were also likely to have fewer antibodies.

It is important to note, however, that this study only focused on immunoglobulin type antibodies, while cellular immunity might still play a role in protection from future infections and needs to be researched further.

READ: Covid 'immunity passports': not ready for prime time?

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