Antigen tests to detect COVID-19 infection at home were a convenient blessing during the pandemic. Instead of waiting in long lines to be tested, and possibly days for a result, testing could be done in the comfort of our homes. But, to date, testing for antibody immunity ─ to determine if you have protection against COVID ─ still needs to be done with trained medical personnel and the use of a laboratory.

That may change. A new study published Monday in Cell Reports Method presents a simple test to detect neutralizing antibodies against COVID-19 using little more than a finger prick and testing cartridge. This may help individuals, especially those with weakened immune systems, decide if they need a booster.

According to STAT News, if the test proves successful in large-scale trials and receives authorization  from regulatory agencies, it could one day offer a convenient and inexpensive way to measure protection against the virus.

Antibodies in the bloodstream are trained search for foreign invaders, like a virus. When a virus does show up in the bloodstream, the specific antibodies neutralize the virus by binding to it and destroying its power to infect cells. The higher the level of antibodies, the more protection you have.

“People want to know, ‘Am I protected today?’ And there isn’t a tool on the market that can facilitate that answer,” said Charles Mace, associate professor of chemistry at Tufts University who was not involved with the new study. While patients can get tested for the presence of antibodies with a prescription from their healthcare practitioners, an at-home test would save time and expense.

Dr. Hojun Li, an attending physician at Dana-Farber/Boston Children’s Cancer and Blood Disorders Center, got the idea to develop a simple method of testing for antibodies when a child’s urgent brain tumor surgery in March 2020 was delayed because of tedious PCR testing.

While other scientists focused on tests that could determine whether or not a person had COVID-19, leading to the antigen tests we have today, Li instead decided to focus on tests for neutralizing antibodies, says Boston's Children's Hospital, that could be done conveniently at home without the need for trained personnel and labs with specialized equipment.

Li and his colleagues developed a simple test kit using paper strips. Users mix a drop of their blood from a finger prick with a solution containing a fragment of the coronavirus spike protein. The fragment, called RBD, is what the virus uses to invade our cells, latching on to the ACE2 receptor on human cells.

Next, users place a few drops of this mixture on the test strip and wait 15 minutes, watching the two lines on the strip. One line picks up free-floating viral RBD protein from the solution. The second, more critical line, picks up antibodies that have neutralized RBD, blocking its ability to initiate infection. The stronger this line, the higher the neutralizing antibody levels and the better protection against COVID-19.

Li believes that the RBD protein could be updated as needed as variants mutate, keeping the test current. He also envisions a smartphone app that could help interpret the results by measuring the intensity of the two test lines. The team of researchers hopes to partner with a company to help manufacture the test kit in bulk and obtain approval from the Food and Drug Administration.

“People who cannot mount a good immune response could test themselves more frequently and perhaps get more frequent boosters,” says Li. “I could also see health officials using the test to measure general rates of immune protection in a community. This knowledge might be useful for decisions about whether public health restrictions or policies are necessary.”