APhA coronavirus watch: Addressing antibody development and reinfection
It’s a popular question these days: Do people generate an antibody response to COVID-19?
In the May 18, 2020, episode of APhA’s 15 on COVID-19 training series, Daniel Zlott, PharmD, BCOP, vice president of professional education resources at APhA, discussed this question as well as the possibility of reinfection with COVID-19.
The short answer is that people do generate an antibody response to COVID-19. The long answer to how that happens involves understanding B-cell immunology.
Within the five different antibody classes, IgM and IgG are the most relevant. IgM usually shows up 4 to 7 days after an individual is first exposed to a pathogen, and peaks 7 to 10 days after initial exposure. Then, it hangs around 2 to 3 weeks before starting to fall off, according to Zlott. On the other hand, IgG can be viewed as a longer-term antibody and can take more time to show up. Once developed, it’s the antibody people produce upon reexposure to the same antigen. “This is where the idea of long-term immunity comes from,” Zlott said.
Researchers conducting a recent cross-sectional study published in Nature Medicine using data from three different hospitals in China found that 100% of the roughly 285 patients in the study developed either IgM or IgG or both within 19 days of COVID-19 symptom onset. Additionally, antibody levels increased for 3 to 4 weeks after symptom onset.
The study, and others that have found similar results, was not able to determine how long the COVID-19 antibody lasts. That’s still an outstanding question, noted Zlott.
The research team also looked to see if there was a difference between patients with severe COVID-19 and those who had mild to moderate cases.
“The only difference they found was in the second week of symptom onset. Patients with severe disease had significantly higher levels of IgG as compared to those who had more mild to moderate cases. Otherwise, there was no difference in the time frames,” said Zlott.
Whether that affects time to recovery or the severity of disease is unclear.
“Over time, as we learn more about the immune response to COVID-19 and what our immune system is doing, we may get a better sense of the role—if any—that IgG plays in that immune response,” Zlott said.
Further, if people have antibodies, questions remain about how long they last and if they can protect against reinfection. A search of the medical literature finds no case reports of reinfection of COVID-19, according to Zlott. The medical literature on reactivation—meaning the virus hangs out or hides away undetected—is murky.
“We still really do not know whether reinfection or reactivation is possible. We need more data and need people to do thorough examinations and explorations of other causes when it appears that there is, in fact, a COVID-19 reinfection or reactivation,” said Zlott.