Key Findings
- Infections with SARS-CoV-2 trigger the generation of antibodies by the body, which wane with time
- Previous SARS-CoV-2 infection may offer protection against reinfection with the virus.
- The production of antibodies may account for the protection offered by this previous infection.
SARS-Cov-2
The risk of reinfection appeared to decline over time, though this may reflect temporary immunity or other factors, rather than increasing protection.
Since the beginning of the COVID-19 pandemic, scientists and doctors have been intrigued by the question, “Why is there a low rate of reinfection with the dreaded SARS-CoV-2 virus?” They wondered if the immunity most people develop following an infection with COVID-19 was due to the production of antibodies by the body’s immune system, and hence a build-up of immunity and protection against the virus. If this is the case, then there is hope for preventing future infections and reinfections and even wiping out the disease completely.
A recently published study by the National Cancer Institute (NCI) revealed that people who were previously infected with SARS-CoV-2 appeared to be adequately protected against reinfection with the virus for a few months. However, in addition to this, this study also observed a possible explanation for this immunity.
How Was This Study Performed?
The study led by Lynne Penberthy, M.D., M.P.H., the associate director of NCI’s Surveillance Research Programme, was focused on understanding whether antibodies detectable following an infection with COVID-19 offered protection against future reinfection with the virus. It also aimed to understand the extent of this protection as regards its duration.
To achieve this, using a retrospective observational descriptive study design, Lynne and her colleagues examined records from December 1, 2018, to August 26, 2020, and identified individuals with a recorded SARS-CoV-2 antibody test done on or after January 2020. These data were obtained from several reliable sources, including commercial laboratories, private insurers and electronic medical records. It is important to note, however, that the researchers considered the privacy of patients’ health information, ensuring that it was protected.
Out of the 3,257,478 patients included in the study, a total of 88.3% had a seronegative index antibody test result (seropositive), while 11.6% had a positive index antibody result (seropositive). On the other hand, however, the antibody index test results of 0.1% were inconclusive (sero-uncertain).
The linked data allowed the researchers to follow up with the participants for a median of 47 and 54 days for the seronegative and seropositive groups, respectively. They then examined the antibody levels and the occurrence of new infections during the duration of this available follow-up time.
Generated Antibodies Following COVID-19 Infection Wane Months Following Initial Detection
The researchers observed that among the seropositive group who were retested during the follow-up period, 12.4% tested negative within 0 to 30 days following their index test.
Interestingly, this value increased to 18.4% when the subsequent antibody test occurred more than 90 days following the index antibody test. These findings showed that antibodies against COVID-19 tended to reduce over time following their stimulation by the virus.
Although antibodies may decline, immune memory, such as memory B and T cells, could still help fight future infections. However, this longer-term immune response was still under investigation at the time.
Generated Antibodies Following COVID-19 Infection Provide a Form of Protection Against the Virus
Considering the relationship between reinfection and previous COVID-19 infection, the authors observed that the rate of new infections in the seropositive group reduced consistently with time during the follow-up period. They reported that within 30 days of the index test, 11.3% of the participants tested positive for COVID-19. This percentage consistently reduced to 2.7%, 1.1% and 0.3% at 31-60, 61-90 and more than 90 days from the index.
It is worth noting that the diagnostic test considered was the Nuclear Acid Amplification Test (NAAT).
In contrast, however, they reported that the percentage of new infections in the seronegative group was relatively constant, remaining at approximately 3% throughout the period of observation.
What are the Limitations of this Study?
While this study provides insight regarding the role of antibodies produced following a SARS-CoV-2 infection against the virus, it is not without limitations. These limitations could affect the applicability of its results. For instance, given the observational nature of the study, it is possible that antibody tests may have affected the behaviours of the participants, invariably affecting the results. Commenting on this, however, the researchers revealed that they believed that it was unlikely that “behaviour differences” could “explain the observed protection” against the virus.
Furthermore, the retrospective nature of the study neglects seropositive individuals who appeared to develop new infections after the index time point or assesses the clinical course of these infections compared with those in the seronegative group.
Nonetheless, this study reveals an interesting finding that is helpful in understanding COVID-19 infections: The risk of new COVID-19 infections is relatively reduced following a previous infection with the virus. The results also suggest a positive role of the duration between an infection with SARS-CoV-2 and a new infection with the same virus in protecting the individual from that reinfection.
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Final Thoughts
Aside from providing insight into SARS-CoV-2, the findings of this study demonstrate the relevance of vaccination against the virus. During vaccination, your body is exposed to antigens normally produced by that organism in such a way that it causes your body to produce antibodies against them. With that first exposure, subsequently, your body learns to recognise that organism in the future. Further studies may, however, be needed to understand the full duration of this immunity and other possible effects of COVID-19 vaccines.
FAQs
How do antibodies against SARS-CoV-2 protect against reinfection with the virus?
While the study does not explore mechanisms through which the generated antibodies against SARS-CoV-2 protect against reinfection with the virus, it is important to note that, generally, antibodies attack and destroy organisms that aim to cause harm to your body. Now, when your body has successfully produced antibodies against a particular organism in the past, it is able to effectively and quickly produce more if there is a reinfection.
Does a decrease in antibody levels mean I lose immunity?
Not necessarily. While it is in fact true that antibody levels tend to wane over time, this study showed that protection against new infections actually improved. This might suggest that other components of the immune system may also be playing a role in the process.
Does a previous COVID-19 infection offer lifelong immunity?
No. Immunity can last a few months but typically declines over time.
How does natural immunity compare to vaccine immunity?
Both offer protection, but vaccines provide more consistent and longer-lasting immunity.
What do memory B and T cells do?
They help the body recognize and fight the virus if it returns, even after antibodies fade.
Can you get reinfected without symptoms?
Yes. Asymptomatic reinfections can happen and may go unnoticed.
Is this study still relevant today?
Yes, as historical context. But updated guidance should come from current health authorities.
References
Harvey, R. A., Rassen, J. A., Kabelac, C. A., Turenne, W., Leonard, S., Klesh, R., Meyer, W. A., Kaufman, H. W., Anderson, S., Cohen, O., Petkov, V. I., Cronin, K. A., Van Dyke, A. L., Lowy, D. R., Sharpless, N. E., & Penberthy, L. T. (2021). Association of SARS-CoV-2 Seropositive Antibody Test With Risk of Future Infection. JAMA Internal Medicine, 181(5), 672–679. https://doi.org/10.1001/jamainternmed.2021.0366
⚠️ Disclaimer: This article discusses research and understanding of SARS-CoV-2 immunity based on data collected between 2020 and early 2021. While it provides valuable insight into early findings about reinfection and antibody response, readers should note that scientific understanding of COVID-19 has evolved significantly since then. For the most up-to-date guidance, consult current publications from the CDC, WHO, or your healthcare provider.
