In a May 26 piece, Smithsonian Magazine reports on the interesting and challenging complexities of moving towards COVID-19 immunity. They note that antibodies fight disease and can also help as evidence of whether a person had a prior COVID-19 infection. The challenge now is that antibodies alone don’t tell us with any certainty about a person’s future prospects if they are re-exposed to the virus: “Researchers still don’t know if antibodies that recognize SARS-CoV-2 prevent people from catching the virus a second time—or, if they do, how long that protection might last.”
General and Specific Antibodies
Like much of life, “immunity isn’t binary, but a continuum,” and “immunity” is not 100% protection, according to virologist Rachel Graham, who studies coronaviruses at the University of North Carolina’s Gillings School of Global Public Health. Antibodies are just one of the body’s many molecular tools against viral infection. Generally, the body “mounts a defense in two acts.” The innate immune response is a “broad-acting ensemble” that attacks anything that does not look like a normal cell. The second act is a slower but specific “adaptive immune response,” molecules which the body custom-builds to recognize the new pathogen.
“This second wave includes antibodies” made by B cells. Some antibodies directly curb a virus’s ability to “latch onto and enter cells,” and others “flag” germs or infected cells, “for destruction by other parts of the immune system.” The direct antibodies, or “neutralizing antibodies,” are a hallmark of a good vaccine. According to Duke virologist and vaccine expert Sallie Permar, most antibodies disappear from the blood “after a few weeks or months,” but the body keeps some of the B cells that make them. So, if the same germ returns, “these cellular factories will whip up a big batch of antibodies to wage a second war.”
Diane Griffin, immunologist at Johns Hopkins University’s Bloomberg School of Public Health, says, “You need an orchestra of responses [for protection] to really be effective.” T cells, “a subset of the adaptive response,” are another important immunity component. Virologist and immunologist at Yale University Akiko Iwasaki points out that the T cells help young B cells, “mature into antibody-making machines.” In addition to this function, T cells also can trigger infected cells to self-destruct.
Challenges in Interpretation of Antibody Testing
Turning to antibody testing, these look for molecules that recognize the spike protein in SARS-CoV-2. Some tests quantify antibody presence, but they don’t determine if they are neutralizing. Harvard microbiologist Marcia Goldberg says a major research problem is that, “laboratory experiments can’t recreate the conditions these molecules experience in the body….” Her points support the importance of antibody trials in COVID-19 patients.
A common misconception is that a positive antibody test means there is no virus present in a person. “Antibodies are often roused about a week into a new infection, potentially overlapping with a pathogen’s tenure in the body. Diagnostic tests that search for the virus’ genetic material can help tease that timeline apart, but even these assessments can yield incorrect results.”
Goldberg explains that at the immune system’s best, it creates “sterilizing immunity, mak[ing] people essentially resistant to reinfection.” But the body reacts to every pathogen differently. Sometimes a second infection is very mild, but will still be contagious.
To date, studies are showing a strong immune response to the virus in both humans and animals. But for now, even the experts are being careful to practice Covid-hygiene even if they have personally gotten and recovered from COVID-19.