Ask the doctors: Coronavirus antibodies used in two new ways

Dear Doctor: I heard on the news about a coronavirus medicine made with blood from people who were sick and got better. But my husband says it’s actually a blood test to see if someone ever had the virus. Who’s right?

Dear Reader: You and your husband are both correct. Two different uses for antibodies have recently been greenlit by the U.S. Food and Drug Administration.

You’re referring to an experimental treatment that was approved on March 24 for very limited use. Your husband is talking about a quick and simple blood test approved by the FDA on April 2. The test, which is already in use in other parts of the world, reveals whether or not someone has been infected with the novel coronavirus. The treatment and the test each rely on antibodies, which are blood proteins that the immune system produces during and after its fight against a foreign invader, such as a virus or bacterium.

Let’s start with the therapy you’re asking about. It’s based on the idea that, when introduced to antibodies used to fight a specific pathogen, a sick person’s immune system will produce those very antibodies. This type of treatment has been in use since the 1890s for diseases such as polio, SARS, Ebola and the H1N1 flu. The idea of using it to treat COVID-19 arises from a very small pilot study – just six men and four women – recently conducted in three hospitals in China.

Each of the patients, who were gravely ill with COVID-19, received a single dose of antibodies gathered from the blood of patients who had recovered from the illness. According to the published research, the treatment resulted in improved oxygen levels and a shorter duration of symptoms in all 10 patients. Most improved within one to three days after receiving the antibodies. The patients also cleared the virus from their bodies more quickly than those who did not receive the treatment. This sounds promising, but it’s important to note that the FDA approval limits treatment to patients who are so ill that they have no other options, and to clinical trials.

The antibody test that your husband is referring to is much closer to a wide release. It uses a pinprick of blood and delivers results in about 15 minutes. Unlike the diagnostic test for COVID-19, which identifies genetic material from the virus itself, this test looks for the antibodies that will be present only if the body has already encountered and fought off the virus. This is valuable information on two fronts. First, widespread use of the antibody test will give scientists a clearer picture of the spread and reach of coronavirus infection in the U.S. Just as important, the test hints at a potential path forward after the height of the epidemic has passed. People who have been exposed to the virus may have some degree of immunity, which would allow them to safely rejoin normal daily life. The challenge here is that, at this time, how much immunity is granted by prior infection, and how long that immunity may last, is not yet known.