Researchers from England recently released the results of the largest antibody study stating that immunity wanes over time. Meanwhile, researchers from the Icahn School of Medicine at Mount Sinai, New York reported that natural coronavirus immunity could last at least five months and perhaps even longer.
The study was published in the journal Science, describing a robust antibody response to the virus for several months. Professor Florian Krammer said that although several studies concluded that antibodies quickly go away, his team found the opposite.
Between March and October, the researchers screened 72,401 volunteers with 30,082 participants testing positive with detectible antibodies. They used the enzyme-linked immunosorbent assay (ELISA) to measure antibodies.
Stable Antibody Response
"More than 90% of people who were mildly or moderately ill produce an antibody response strong enough to neutralize the virus, and the response is maintained for many months," Krammer said. These results are necessary for vaccine developers to understand. At the moment, some pharmaceutical companies have claimed that their vaccine candidate can provide immunity for up to one year.
Not opposing the study by Imperial College London, the American researchers explained that measurements that show waning immunity months after infection could be just the first wave. Sometime after, there is a second wave of defenses in the immune system that will produce a stable antibody response to coronavirus.
Over 90% of the screened volunteers had moderate to high levels, also known as titers, of antibodies to the virus' spike protein. The researchers then studied the antibodies of 121 patients who recovered and donated their plasma a few months after initial symptoms.
Dr. Ania Wajnberg said, "The serum antibody titer we measured in individuals initially were likely produced by plasmablasts, cells that act as first responders to an invading virus and come together to produce initial bouts of antibodies whose strength soon wanes." Stable antibody levels were most likely produced by plasma cells from the bone marrow, similar to how the body responds to other viruses.
Lasting Immunity
Although antibodies are the first line of defense in the immune system against infection, researchers remain uncertain about the chances of getting reinfected. However, stable antibody responses lower the chances of reinfection.
For now, cases of reinfection remain rare. Pharmaceutical companies around the world are still conducting clinical trials to develop vaccines with long-term immunity, and if possible, permanent immunity.
The best-case scenario for coronavirus vaccines would be to have a single or double dose that would give lifelong immunity such as measles and hepatitis B vaccines. However, respiratory viruses are more complex, such as seasonal flu.
Wajnberg's team wrote that based on human coronaviruses where neutralizing antibody production is triggered, the antibodies provide protection for several years and have prevented reinfection. For now, there is not enough evidence that antibodies can protect the body from the reinfection of Covid-19 or how long the immunity would last.
It is critical to conduct studies that establish a correlate of protection or compounds from the blood that indicates immunity. Alongside a better understanding of antibodies associated with the spike protein, a correlate of protection would help with the development of effective vaccines, concluded the authors.
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