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Immunity after COVID-19 infection

 How Long do Antibodies Last After Infection

    As of November 2020, there have been over 47 million COVID-19 cases worldwide. Many of these 47 million individuals may be wondering if it's possible to be infected with COVID-19 more than once. The answer is yes (see First COVID-19 Reinfection in US). However, a recent study published on October 28, 2020 in the journal Science, provides information about a possible period of COVID-19 immunity in infected patients. This study answers some of the most pressing questions surrounding the coronavirus infection: Do antibodies remain active and create immunity to the virus after initial infection?  If so, how long does this immunity last?

Background

   Antibodies are proteins produced by the immune system to fight off viruses and bacteria. This study focuses specifically on the anti-spike antibody which targets the 'spike' protein on the surface of the coronavirus, known to be critical for virus entry. Scientists hypothesize that after a patient is exposed to COVID-19 and has developed antibodies to fight off the virus, the patient may have stronger and higher antibody levels to provide protection from a second infection. However, not much is known about the protection/immunity antibodies may provide or how long it lasts. 

Study Results: Antibody levels

    Researchers obtained and analyzed the data of 30,082 (mild to moderate) COVID-19 infected individuals who volunteered as donors for convalescent plasma from the Mount Sinai Health System in New York. Antibody titers (concentration of antibodies) for each patient were analyzed and categorized into 3 groups: low, moderate and high. Titers of 1:80 and 1:160 were defined as low titers, 1:320 as moderate, and 1:960 or  >1:2880 as high titers. Of the 30,082 patients, 7.12% had low titers, 22.49% had moderate titers, and 70.39% had high titers. 
    However, scientists need to determine whether or not the antibodies are active in eliminating the virus. This process is called neutralization. Using a microneutralization assay, neutralization titers were measured and found to have a significant correlation with antibody titers. As antibody levels increase, so do the neutralizing effects of the antibodies. 

According to the study, a vast majority of patients have moderate to high levels of antibodies and experience a 'robust' antibody response to coronavirus spike proteins.  

Study Results: Antibody duration

    To determine the duration of the antibody response, researchers utilized the data of 121 plasma donors. These individuals were screened 30 days after initial symptoms and again at two additional points in time. The average interval between the first and second titer measurement was 52 days. The second measurement occurred around 82 days after initial symptoms and the third measurement after 148 days.
    Results of the data analysis found that patients in the higher titer range (1:2880 and 1:960) had a slower decline in titer over time compared to patients of other titer levels. Those with initially low or moderate titers maintained a relatively stable titer approximately 5 months (148 days). 


Summary

   In summary, the study finds that patients infected with mild-moderate COVID-19 develop robust antibody responses which last for approximately 5 months in patients will initially low-moderate antibody titers. However, these findings are only true to this study and scientists believe more research needs to be conducted before a definite conclusion can be drawn on whether initial infection prevents reinfection from COVID-19 and for how long.

Sources

1. Wajnberg, Ania, et al. “Robust Neutralizing Antibodies to SARS-CoV-2 Infection Persist for Months.” Science, American Association for the Advancement of Science, 28 Oct. 2020, science.sciencemag.org/content/early/2020/10/27/science.abd7728. 

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