Officials in Spain's capital rekindled the debate on so-called immunity passports on Tuesday as a way to avoid reintroducing a strict lockdown after imposing new measures to counter a flare-up in new COVID-19 infections.
Madrid President Isabel Diaz Ayuso told reporters the region is developing immunity passports to be delivered to people who have successfully recovered from the disease and have antibodies.
The World Health Organization (WHO) has previously cautioned against the use of such a document.
Diaz Ayuso said that passport holders would be able to ignore confinement rules and access gyms, museums, cinemas and other indoor public places.
"The key is that those who cannot infect others can have a normal life and take precautions for the vulnerable," Diaz Ayuso said.
"We ask that this document be studied, allowing us to demonstrate who at the moment cannot and will not be infected," she went on, adding: "It is a model that Spain and other countries should export."
The experimental measure is to be rolled out in September.
No consensus on immunity passports
But there is no consensus on immunity passports, not even in Spain.
The national Minister for Health, Salvador Illa, told reporters on Tuesday evening that "no international organisation, nor any of the documents that we have prepared contemplate this type of actions."
WHO stressed in a scientific briefing released in April that there was no evidence people who have recovered from COVID-19 and have antibodies are protected from a second infection.
They warned then that people who assume they are immune to a second infection may ignore public health advice and that immunity passports could instead increase the risk of continued transmission.
Several studies have since been released on the issue.
One from the University of Amsterdam advanced that immunity to reinfection from human coronaviruses may last only six months. Researchers argued that if SARS-CoV-2 — the virus that causes COVID-19 — behaves like other strains of coronavirus then a similar pattern may be expected.
Another study, released earlier this month by the University of California at Los Angeles (UCLA), found that in people who have recovered from mild cases of COVID-19, antibodies against the virus drop sharply over the first three months after infection, decreasing by roughly half every 36 days.
"The findings raise concerns about antibody-based 'immunity passports', the potential for herd immunity and the reliability of antibody tests for estimating past infections. In addition, the findings may have implications for the durability of antibody-based vaccines," researchers said in a statement.
Cases in Spain double in a week
Diaz Ayuso's comments about immunity passports came as she introduced new local measures to stem the spread of the virus following a recent spike in new cases.
Wearing face masks is now mandatory in all public places, including outdoor terraces. Social gatherings, both public and private, have been reduced to 10 people while bars and nightclub must close at 01.30 am.
Madrid accounted for 1,381 cases when it had registered just 579 the week prior.