- Experts say a person may still have immunity protection against COVID-19 even if antibodies aren’t present.
- They say antibodies can be reproduced quickly during exposure, and T cells and other body defenses can also be effective.
- They say the antibody response to COVID-19 does affect how often vaccines may need to be administered.
A recent spate of reports and studies suggest that antibodies produced after having COVID-19 might not last long — perhaps from a few months to just a few weeks.
This raises concerns about our ability to build immunity to COVID-19, at least by natural means, as well as heightening concerns about the potential for reinfection.
“The results call for caution regarding antibody-based ‘immunity passports,’ herd immunity, and perhaps vaccine durability,” a recent correspondence in the New England Journal of Medicine stated, although the column noted further study is needed.
But antibodies aren’t the be-all and end-all of conferred immunity, experts say. And it’s still early days in the study of SARS-CoV-2, the coronavirus that causes COVID-19.
“Existing antibody research shows that the strength of the immune response correlates to the severity of the symptoms. The sickest individuals tend to have more antibodies circulating in the bloodstream compared to those with mild or no symptoms,” said Chris DiPasquale, director of assay development at Babson Diagnostics, a Texas company doing COVID-19 serology (antibody) tests.
A person’s immune system involves a complex array of interrelated cell actions, productions, and associated responses to defeat a disease.
When a body encounters a virus, B cells, aided by “helper” T cells, create neutralizing antibodies that attack and destroy future instances of the virus before a person gets sick.
These antibodies are among the easiest to detect and thus have been the most commonly reported measure of COVID-19 immunity.
But two types of T cells, which are harder to measure, also play an important role in determining immunity and aren’t always perfectly correlated to antibody levels.
One preprint study from researchers at Strasbourg University Hospitals in France, for instance, found T cell responses in people with COVID-19 even when antibody tests came up negative.
Thus, “T-cell responses may be more sensitive indicators of SARS-Co-V-2 exposure than antibodies,” the researchers wrote.
Finally, a further study in the journal Nature found antiviral responses that go beyond these immune cells altogether.
In terms of developing a strong COVID-19 vaccine, the way our bodies’ natural immune systems react might not have as strong a bearing on vaccine effectiveness as common sense dictates.
“I don’t think the fact that people who are asymptomatic are not having a durable antibody response says anything about what’s going to happen with a vaccine,” Linda Thompson, PhD, an immunologist at the Oklahoma Medical Research Foundation, told Healthline.
“We know with flu that measuring antibodies in the blood can give you a good idea about whether someone’s going to be protected. We really have no idea for this virus, whether measuring antibodies in the blood is going to tell you who’s protected or not,” she explained. “You could still have memory B cells that are hiding out in the lymph nodes or the bone marrow that can rapidly divide and make antibodies.”
One common theme with existing COVID-19 research is that we still don’t have enough time or data to effectively and thoroughly understand the disease.
“One has to be cautious in making any long-term extrapolations,” Dr. Daniel B. Fagbuyi, an emergency room physician and former Obama administration biodefense and public health expert, told Healthline.
“What is defined as a good antibody response? What should be measured in the commercial antibody tests? How often and how many vaccines will elicit a ‘good’ vaccine response when we get a vaccine?” he said.
One thing that fading antibodies might indicate, however, is the need for a series of shots and perhaps regular “re-ups” of vaccination once one is available.
“If a relatively brief antibody response proves to be common for COVID-19, a vaccine may need to be administered at least a few times each year,” said Dr. Don L. Goldenberg, an emeritus professor of medicine at the Tufts University School of Medicine in Massachusetts and the author of “How the COVID-19 Pandemic Is Affecting You and Your Healthcare.”
Even with evidence of fading antibodies, reinfection with SARS-CoV-2 is unlikely because of what we generally know about immune reaction to viruses, researchers say.
“In some patients, persistent remnants of inactive viral particles may trigger a persistently positive PCR test, and patients then may think they have a reinfection,” Goldenberg explained. “There have been recent cases that do likely represent a true reinfection, although this does seem very unusual.”
For most, it’s simply that the pathology of this virus isn’t well understood. What might seem like reinfection could simply be longer-term effects of the virus, or reemergence of viral propagation inside someone who feels better but never fully cleared the effective virus from their system.
“In 2020, nothing is unusual. We are just beginning to learn about the human body’s response to SARS-CoV-2, and across the spectrum of human individuals, each person’s response is nuanced and individualized,” DiPasquale told Healthline.