Testing the public to determine who has already had coronavirus could help governments to determine when to ease lockdown measures and send people back to work.

These blood tests - also known as serologic or antibody tests - would be different from the current coronavirus tests being carried out and paint a more accurate picture of how the pandemic has unfolded.

"There are immune memory cells (antibodies) that remain in the blood after infection and are specific for the virus, they are what we would look for,” Dr Caroline Buckee, an associate professor of epidemiology at Harvard’s School of Public Health, told Euronews.

Most of the current COVID-19 tests instead involve a nose swab sample to determine if a person is actually carrying the virus. Those swabs of mucus are then analysed, often by a laboratory process, to find the virus.

But a serologic test could instead determine who has already had the virus or been exposed to it by searching for a person's levels of antibodies: proteins developed by the immune system to attack invaders such as bacteria or viruses.

"The key is whether those antibodies actually protect against infection; we still don't know that,” Dr Buckee added, meaning that experts are still looking at whether or not people who have recovered from the illness can get it again.

Many experts expect that people who have recovered from the virus will be immune for some time.

“A person who has already [had] the disease develops a fairly high level of antibodies and will be immunised for some significant period of time,” said Dr María José Sierra from Spain’s Coordination Centre for Health Alerts and Emergencies on Sunday.

That’s why many countries are setting out to invest in antibody testing to determine what proportion of their population may be immune to the virus.

Some laboratory companies in Europe and the United States have just begun to roll out commercial versions of these tests which will likely be more available in the weeks to come.

The US Food and Drug Administration issued its first authorisation for an antibody blood test just this past week.

Determining population immunity could help to ease movement restrictions

Dr Jenny Harries, the Deputy Chief Medical Officer for England, said that antibody testing would be crucial to determining when the lockdown could end.

“If we know how many people have already had it, we will understand the proportion of the population that could still get it and that gives us the clue to a number of things,” she said, including how many people would still need to be vaccinated against the virus and what proportion of the population was already immune.

She said testing was starting among some age groups “so that we can start to get a good idea of how many people have had it and then extrapolate that number out so we get a picture of the whole country.”

The UK’s health minister Matt Hancock, who recently recovered from COVID-19, said at a press conference that the government was considering immunity certificates so that people could return more quickly to normal life.

And these blood tests will give much faster results than a nose swab test, making it easier to conduct mass testing.

“The important part about serologic testing is it’s much, much, much, much, much easier to deploy. And you can think about it as a sort of pregnancy-test-like deployment of it,” said Sarah Fortune, Chair of Harvard University's Department of Immunology and Infectious Diseases.

“I think it’s going to be an important way to try to understand where we are in the epidemic as it rolls forward because it helps us understand in a much more feasible fashion how we’re doing and whether we’re allowing enough progression, that we are getting enough herd immunity that we’re moving towards a protected population,” she added.

This “herd immunity”, meaning that enough of the population is immune to the virus to prevent them from becoming infected again, could be the only way to prevent against a resurgence of COVID-19.

Many scientific models to predict the outcome of the pandemic have determined that once social distancing restrictions - currently in place for more than half of humanity - are lifted, cases could go back up again.

But if many people have developed antibodies to the virus, this could prevent a second wave of the epidemic.