Remember all the hype about so-called "immunity passports" getting the travel world back on track?
Governments are still exploring whether certificates, wristbands or mobile apps could get those who have recovered from Covid-19 working and traveling again.
But the notion that immunity passport holders would be able to travel the world carte blanche, going mask-free on airplanes and touring empty museums and amusement parks with no fear of infection, was short-lived.
Immunity passports may appear a good plan in principle, but experts are now sounding the alarm against them.
Much ado was made when air carrier Emirates began trialing antibody finger-prick tests to a small subset of passengers in March. But when accuracy rates were found to be around 30%, the Dubai Health Authority, which had been administering the tests, banned the testing altogether.
Think 30% is low? It gets worse. A report by more than 50 scientists found that of 14 antibody tests on the market, only three provided consistently reliable results (and even those three had issues).
The Foundation for Innovative New Diagnostics (FIND), a global nonprofit diagnostics organization, estimates over 250 antibody tests have been commercialized to date, with more than 30 currently in development.
Following criticism that it allowed a glut of dubious antibody tests to flood the market, the U.S. Food and Drug Administration announced in early May that antibody test makers had 10 days to provide accuracy results or face removal from the market.
On May 21, the FDA removed some 31 antibody tests from the agency's official "notification list," a decision lauded by FDA Commissioner Stephen M. Hahn as "an important step the agency has taken to ensure that Americans have access to trustworthy tests."
Even with reputable test kits, one may not be enough. The FDA states that a single antibody test isn't likely to be sufficiently accurate to be able to tell whether members of the general population have Covid-19 antibodies. It recommends a second test — ideally one that assesses antibodies to a different viral protein — to increase the accuracy of the results.
Unsurprisingly, erroneous results can have profound ramifications. An article published by the Johns Hopkins Bloomberg School of Public Health on April 22 states: "A false negative may prevent an individual from returning to work; a false positive might lead to an epidemic chain."
Noting these inaccuracies, the eight contributing authors of the article concluded that immunity certificates are "not a justifiable step at this time."
Assuming testing accuracy improves, immunity passports have another huge hurdle to surmount, and that is understanding what the results actually mean.
While some antibodies confer decades of immunity to viruses (measles and chickenpox, for instance), this isn't the case for coronaviruses, due in part to their ability to mutate over time.
The World Health Organization (WHO) issued a brief in late April stating there is no evidence that those infected with Covid-19 are protected against a second infection. Two days later, however, it clarified in a tweet that it expects antibodies to provide "some level of protection."
The WHO also cautioned that antibody tests must be able to distinguish between past infections from SARS-CoV-2, the virus that causes Covid-19, and the other set of six human coronaviruses, two of which are MERS and SARS (of which antibodies convey immunity on average for one and two years, respectively). The other four cause the common cold; those who recover from those more mild coronaviruses can expect little immunity to subsequent infections.
In the end, Covid-19 antibodies likely do convey some protection against reinfection, but to what extent and for how long is still unknown. This makes the prospect of widespread use of immunity passports "not very likely," says Dr. Sharona Hoffman, a bioethics professor at Case Western Reserve University's School of Medicine.
"If the tests become more reliable, immunity passports may become reality," said Hoffman. "But it is more likely that we will have to wait until we have a vaccine."
Dr. Peter Gulick, an infectious disease expert at Michigan State University's College of Osteopathic Medicine, agrees.
"At this point in time, we don't know how long these antibodies last, whether a few months or a year," he said. "Once we have a vaccine, requiring proof of vaccination, as well as proof of a protective antibody, will be much more meaningful and safer for travel."
While medical studies continue, the travel industry isn't standing idly on the sidelines. Eager to get planes in the air and hotels opened, the travel industry is formulating novel ways to entice travelers back, walking the line between ensuring customers' safety and unnecessarily inconveniencing their trips.
Rather than courting those with positive antibody test results, some are opting for more accurate nose swab molecular tests, also known as PCR tests, which detect active Covid-19 infections. The Telegraph reported last week that the Maldives plans to reopen to tourists in July with plans to make molecular Covid-19 tests compulsory for all tourists. Sha Wellness Clinic, a medical clinic and hotel in southeastern Spain, is requiring all guests to provide two negative tests — one taken several days before arriving and another upon checking in.
Most countries and companies that are reopening for summer travel are opting for less invasive options, such as health screenings, increased cleaning and social distancing guidelines. Notably though, travel is marching on, and the absence of immunity passports doesn't seem to be holding airlines, cruise companies or hotels back.
Immunity passports are attractive for anyone who yearns to get back to life as usual (i.e. all of us), but consider the ramifications of a certain sector of society being able to move, congregate, travel and work freely — while the other cannot.
This was the subject of an article in the respected medical journal "The Lancet." Vulnerable populations, such as those unable to afford extended periods of time without work, might be motivated to seek out infections, which could exacerbate existing racial and gender inequities, not to mention infection rates. Proof of immunity could become a condition for hiring, and a black market for fraudulent immunity documents could develop.
In addition to discrimination concerns, author Alexandra L. Phelan distinguishes between the WHO's Carte Jaune, or Yellow Cards (which show proof of vaccinations), and immunity passports by stating: "Vaccination certificates incentivise individuals to obtain vaccination against the virus, which is a social good. By contrast, immunity passports incentivise infection."
Similar situations developed during yellow fever outbreaks in the U.S. during the 19th century, which resulted in those who had not been exposed to the illness being denied employment and housing.
"City residents in that era did try to prove that they had been exposed to yellow fever in order to get jobs," said Hoffman. "People sought exposure and hoped to live through it to be deemed acclimated and have work opportunities. But a lot of them died after being exposed."
The U.K. is piloting a passport program that uses testing and facial biometrics to identify those with Covid-19 antibodies (though the emphasis appears to be on working, not traveling), while Germany decided to seek advice from its national ethics council before using millions of antibody tests it purchased from Swiss pharmaceutical company Roche.
If immunity passports are issued, there may be populations who do not have access to antibody tests or the means to pay for them, said Hoffman.
"Hopefully, we will have a program that would make antibody tests very accessible, perhaps even free to people who do not have health insurance."
For immunity passports to work, there have to be enough people who have them to make a meaningful effect on the travel industry.
While the countries with the highest Covid-19 infection rates — namely, the United States, Brazil, Russia, Peru, India and parts of western Europe — may have the best reason to create immunity passports, the number of those who have recovered in those countries may not be enough to make the development of a program worthwhile.
Though this varies by region, it's estimated that no more than 5% of these populations have antibodies (by contrast, around 70% of the population needs to have antibodies, either through recovered infections or vaccinations for herd immunity to kick in).
Countries that have successfully "flattened the curve" — such as Australia, New Zealand, Vietnam, Hong Kong and Taiwan — have even fewer cases, and thus less incentive to create an immunity passport program.
Though they may not be a golden ticket to travel the world, antibody testing is critical for other reasons. It can track the extent of the pandemic in certain regions, improve modeling data and (eventually) determine which front-line workers can work alongside infected people.
Singapore has effectively used antibody tests to trace Covid-19 clusters. People with antibodies can donate plasma to help those currently fighting the disease and be prioritized later for vaccinations if it's determined they already have some level of immunity.
Rather than immunity passports, digital "health passports" — which could contain positive antibody test results, recent negative Covid-19 test results and eventually, proof of vaccination — may be a more useful type of travel document to carry in the future.
Health passports could alleviate some, but not all, of the problems inherent in immunity passports, though privacy considerations and international cooperation would have to be dealt with to make any health passport program work.