Even if you’ve gained some immunity to covid-19 by getting vaccinated or recovering from the disease, it’s hard to know how vulnerable you might still be. Now MIT researchers have developed an easy-to-use test that may reveal just that. Using the “lateral flow” technology familiar from home covid and pregnancy tests, it measures the level of neutralizing antibodies against the SARS-CoV-2 virus in a tiny blood sample collected from a finger prick.

Easy access to this kind of test could help people determine what kind of precautions they should take, such as getting an additional booster. “Among the general population, many people probably want to know how well protected they are,” says Hojun Li, a physician and a lab head at MIT’s Koch Institute for Integrative Cancer Research, the senior author of a paper on the technique. “But I think where this test might make the biggest difference is for anybody who is receiving chemotherapy, anybody who’s on immunosuppressive drugs for rheumatologic disorders or autoimmune diseases, and anybody who’s elderly or doesn’t mount good immune responses in general.”

Li normally studies blood cell development and how blood cells become cancerous, not infectious diseases or diagnostics. So to develop this test, he sought advice from MIT faculty members Hadley Sikes and Sangeeta Bhatia, SM ’93, PhD ’97, who have expertise in the technology. With their help, his lab developed a device that can measure the amount of antibodies that block the SARS-CoV-2 receptor binding domain (RBD) from binding to ACE2, the human receptor the virus uses to infect cells.

The first step in the test is to add the blood sample to viral RBD protein that has been labeled with tiny gold particles. A few drops of the sample are then placed on a paper strip with two test lines embedded in it.

One of these lines attracts free viral RBD proteins, while the other attracts any RBD that has been captured by neutralizing antibodies. A strong signal from the second line indicates a high level of neutralizing antibodies in the sample, meaning you’re well protected. The results can be read in about 10 minutes. For a more precise measurement of antibody levels, a smartphone app can measure the intensity of each line and calculate the ratio of neutralized to infectious RBD protein.

When the researchers tested their device in about 60 people who had been infected with SARS-CoV-2 and 30 who had not, results were similar in accuracy to lab tests. The team also tested a series of samples from two people before they received a vaccine and at several points afterwards. Their level of neutralizing antibodies peaked around seven weeks after the first of two doses and then slowly declined to about 10% of the peak.

The test could be easily adapted to different variants of SARS-CoV-2 by swapping in new proteins, Li says. The researchers now hope to partner with a diagnostics company that can license and manufacture large quantities of the tests and obtain FDA approval for their use.