Europe hopes that antibody tests will be the panacea to ending lockdowns. But the scientists arent convinced.
Advocates tout these tests, which look for antibodies produced by someone infected with the virus, as the key to letting people return to work. Countries across Europe are working to roll them out, with promises of millions of tests becoming available in the coming weeks and months.
The oft-repeated assumption is that antibody (or serological) tests, which are most useful for knowing if someone previously had the coronavirus, also indicate immunity to it.
“Everyones waiting for serologic testing, the whole world,” said Frances Health Minister Olivier Véran, as reported by AFP. He believes mass production of the tests could start within weeks and would be important in reducing confinement.
Even the European Commissions roadmap to exiting containment measures relies on these tests.
“While its undeniably a good sign, merely having some antibodies does not necessarily prove immunity, as is often casually asserted.” — Simon Clarke, associate professor at the University of Reading
They “will provide complementary data on the share of the population that has successfully overcome the disease and eventually measure the acquired immunity,” it reads.
In Germany, the Robert Koch Institute (RKI), which monitors infectious diseases, announced last week it plans to carry out three different types of antibody test studies among different groups, in different regions and with different sample sizes. One aim is to find out whos immune, including among those who might not be aware they were even infected.
Antibodies ≠ immunity
Theres one major caveat. Merely having antibodies doesnt signal immunity.
“You cant say just because someone has antibodies that they are immune,” said David Cavanagh, senior lecturer at the University of Edinburghs Institute of Immunology and Infection Research. “We just honestly have not enough idea of whether everyone will be immune after infection or not at the moment.”
Experts in the U.S. are also at pains to emphasize this.
Antibodies can be made against any individual component of a virus. Some of these antibodies confer immunity, others may not, explained Cavanagh.
“When you make an immune response, you can make very effective immune responses, or you can make ineffective immune responses,” said Cavanagh.
He explained that these antibodies could neutralize the virus by blocking its entry into cells, or they could aggregate the virus together so it can be destroyed by the bodys immune cells.
Other antibodies, however, could bind to the virus but not actually stop it from invading the cells. Instead, they would promote infection.
Another issue is the timing of when tests are carried out. Lothar Wieler, the RKIs head, warned last week that despite the tests many advantages, some might also “raise false hopes.” For instance, in most cases, antibodies can only be detected at the soonest one to two weeks after an infection — so tests carried out at an earlier stage might be misleading, according to his institute.
A broader difficulty: Scientists just dont know enough about the coronavirus yet to say which antibodies are likely to be effective, as its a novel virus.
For example, preliminary findings looking at the presence of antibodies in residents in Gangelt, a town in a hard-hit region in western Germany, indicated that 14 percent of the population had been infected.
Some media reports called this figure a representative finding for the broader population because 400 households across the town were included. But others criticized the preliminary results for being published too early.
Simon Clarke, associate professor in cellular microbiology at the University of Reading, said that the study “does not in any way prove that 14 percent of the population are immune.”
“While its undeniably a good sign, merely having some antibodies does not necessarily prove immunity, as is often casually asserted,” he said. We dont know what the correlates of protection are, and we dont know how long any immunity would last, he added.
In particular, what Clarke and other scientists are cautious about is overinterpreting the results, and the possibility of those tests delivering false positives.
Indeed, other similar studies also show that the picture isnt clear cut.
David Heymann, an epidemiologist who headed the global response to SARS in 2003 and is now at the U.K.s Chatham House, has pointed to Chinese data indicating that, in some parts of the country, people have developed either very low levels of antibodies or none at all.
The question remains open whether milder infections produce fewer or no antibodies, or whether the virus is less easily transmitted than previously thought, he noted at a Chatham House webinar April 15.
Getting them to work
Theres another big problem. Plenty of tests found on the European market at the moment arent working very well.
For instance, scientists worry about the sensitivity of at-home versions of antibody tests, which arent as precise as lab tests and cant tell you how much of an antibody response you had.
The head virologist of Germanys Charité clinics, Christian Drosten, warned in a video recorded for the German health ministry that those home tests “come in very different quality.”
“There are a lot of companies, especially from Asia, which offer these types of tests,” Drosten said, noting they would look “like a pregnancy test.”
“We will have to maintain some level of social distancing, a significant level of social distancing, probably indefinitely until we have a vaccine available.” — Neil Ferguson, epidemiologist
But some of those versions arent validated yet, he explained, which means they cant be compared to standardized lab tests.
“We are experiencing surprises” when it comes to the results of those home versions, he added. “Some work very well. Others are really useless and you really shouldnt use them, because you have a very high risk of not detecting the infection.”
Meanwhile, some EU countries — including Belgium, Finland, Sweden, Ireland, Germany and the Netherlands — have warned against or even banned self-tests for coronavirus at this stage, according to a