What are antibody tests and can they get the world back to work?

They’ve been held up as key to resuming life as we know it by public figures, including the Governor of New York, Andrew Cuomo.

While some experts and policy-makers have cast doubt on their accuracy, it looks like antibody tests will be with us soon, as companies and governments around the world invest in production and fast-track approvals.

So how do they work and could they really help people and economies end the lockdown?

What are antibody tests?

In simple terms, antibody tests - also called serology tests - show who has been infected and recovered. The body makes antibodies in response to many illnesses, including COVID-19.

The tests searching for valuable IgG antibodies come in two main forms: rapid tests and assays.

The most simple rapid tests can be used at home, typically involving pricking a finger and they can get results in minutes.

Assays - which involve sending blood samples to a lab for analysis - are generally more accurate but take much longer. So governments ideally want good rapid tests.

How useful are the antibodies?

That is not yet fully understood. Whereas childhood infection by chicken pox can give long-lasting immunity, it is unclear how long COVID-19 resistance lasts.

And while most people who contract COVID-19 appear to produce antibodies, experts are unsure how long they remain and whether they have enough power to protect against future infections.

The hope is that COVID-19 antibodies will behave in a similar way to those the body makes against SARS, a disease that has a lot of similar genetic material. Immunity against SARS peaks at around four months and offers protection for roughly two to three years.

How soon will we see antibody tests?

Tests are already being used in some countries that were hit early by the virus. In Wuhan, China, where COVID-19 first emerged, people returning to work are being tested so authorities can build a picture of immunity.

In the West, their use is not yet widespread, although some organizations are now rolling out tests to frontline staff, with one private British medical clinic urging the government to invest in inexpensive South Korean Sugentech kits.

However, this caution is changing. New York’s Cuomo has announced 2,000 tests a day for the city’s frontline workers; he plans to expand that to 100,000 a day.

Across America dozens of manufacturers are seeking fast-track Food and Drug Administration approval for both lab-based and more rapid point-of-care antibody tests. US health authorities expect the tests to be available in a week, subject to FDA approval.

But elsewhere there has been more caution. The UK has bought 3.5 million antibody tests, but has not yet found one reliable enough for widespread use.

What are the concerns around antibody tests?

While antibody testing has been a pillar of many governments’ strategies for economic recovery, there are worries about the accuracy of the tests, particularly rapid testing kits.

The UK says its tests on various antibody testing technologies have been disappointing, failing to spot those who have had milder cases of the virus.

Elsewhere there are concerns that in some governments’ haste to ease economic restrictions, decisions to approve test kits could be rushed. In America, for example, the FDA is allowing tests to be developed without standard review procedures, although the FDA says it is reviewing test data.

Some researchers have also questioned the strength of antibodies and whether they will be strong enough to fight the virus. Researchers at Fudan University in Shanghai analysed blood samples from 175 recovered coronavirus patients after they were discharged from hospital and found surprisingly low levels of antibodies against the virus.

However, these are preliminary results, not yet published in a journal; further research is necessary.

Could the tests ease the lockdown?

Early on, many governments saw antibody testing as a cornerstone of the phased easing of lockdowns.

Last month, Germany was one of many countries reportedly considering issuing ‘immunity certificates’ based on testing.

However, with concerns persisting about the potential for false positives and false negatives in tests, it looks like in the short term at least, antibody tests can only play a supporting role in lifting restrictions.