As a world besieged by COVID-19 waits in hope for a vaccine that may or may not come, antibody tests could be the next best thing.

The finger prick tests with rapid results, which are already being used in some populations, can detect people who have already been exposed to coronavirus – and are perhaps now immune – and lead to a quicker resumption of life as we knew it.

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As it’s unclear how many people have been infected without realising, antibody tests could reduce the risk of a surprise outbreak when lockdowns lift, by clearing those who may now be immune and identifying those who aren’t.

That could be especially useful for workers in key areas, such as health care, who may still be at risk of contracting the virus.

Many governments have rushed to buy millions of antibody tests as they plan their virus exit strategy. UK Prime Minister Boris Johnson called the tests a “game changer” and ordered 3.5 million home tests from various Chinese companies.

This week, New York Governor Andrew Cuomo announced a massive rollout of antibody testing in the virus-ravaged state. Testing in New York has already found far more people had COVID-19 than the number confirmed in labs.

In Los Angeles, antibody testing revealed the rate of infection was up to 40 times higher than official numbers.

Australia’s Health Department said last month “point of care” tests that detect antibodies were coming soon, but they’re yet to be rigorously tested by the Therapeutic Goods Association.

China announced this week it would ramp up virus and antibody testing on key populations to limit the chance of another outbreak as people returned to work and school, the South China Morning Post reports.

The tests have the added bonus of generating data that could be used in epidemiology studies and research into prevention, Guangzhou Medical University president Wang Xinhua told the Post.

“Through testing for antibodies we can understand how many people have it, and how the antibody changes over time, as well as the immune response caused by the virus – does it become weak after a few months, or does it exist in the long term?” he said.

With government desperate to reboot their economies and billions of people itching to return to workplaces and communities, antibody tests sound like the silver bullet we’ve been hoping for.

But the concept has already hit some major roadblocks and risks giving us false – and potentially dangerous – hope.

The head of the World Health Organisation’s emergencies program Dr Mike Ryan has urged countries using antibody tests to be careful about relying on results as there was “lots of uncertainty” about them.

For starters, in the rush to find a fix for COVID-19, the market has been flooded with test kits of sketchy quality and accuracy. There are a lot of duds.

The 3.5 million antibody tests the UK government ordered from China last month turned out to be unreliable.

Part of the problem is the lack of rigorous testing. Laboratory microbiologist Peter Collington from the Australian National University told Nature magazine the kits need to be trialled on massive groups of people, including hundreds that have had COVID-19 and hundreds who haven’t.

So far, most tests have been carried out on just “tens of people”, Nature reports.

But one of the biggest dangers with antibody testing lies in the expectation of immunity.

Scientists don’t yet know if you can catch COVID-19 twice, and they don’t yet know if you can’t. And it’s not clear if all people with the virus develop the specific neutralising antibodies that would prevent it from reinfecting them.

Last week, the World Health Organisation said there was no evidence people who recovered now have immunity to COVID-19.

US coronavirus expert Anthony Fauci, who is on the White House COVID-19 taskforce, said it was a “reasonable assumption” antibodies meant protective immunity, but it wasn’t yet proven with this virus.

“We don’t know how long that protection, if it exists, lasts,” he said on Good Morning America. “Is it one month, three months, six months, a year?”

Dr Fauci said “we still have a way to go” with antibody tests.

“The problem is that these are tests that need to be validated and calibrated, and many of the tests out there don’t do that,” he said,

“So even though you hear about companies saying (they’re) flooding the market with these antibody tests, a lot of them are not validated.”

There is also the question of timing. Scientists don’t know enough about COVID-19 to say for sure at what point an infected person develops antibodies, so an ill-timed test may produce inaccurate results.

There is also the risk of false positives from a test that picked up other antibodies, separate to the ones that fight COVID-19.

Prof Collington from the Australian National University told Nature it took years until antibody tests for HIV were developed that had more than 99 per cent specificity.

With countries poised to make major decisions guided by antibody testing – some countries are already talking about issuing “immunity passports” to cleared citizens – scientists urge caution.

The Australian Medical Association’s South Australia president Chris Moy told the ABC there was a real danger of antibody tests giving people false assurance.

“A negative test does not mean you haven’t had it at the time. That’s the biggest concern at the moment, it gives you false assurance,” he told the ABC.

“A test which doesn’t give you the information that you want, which is whether you’ve actually got it at the time, is worse than no test at all.”