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Your body will make different antibodies in response to coronavirus infection than in response to vaccination.
One of these antibodies is called a “spike antibody,” meaning that the antibody is directed at the spikes that surround the virus’s outer shell. The antibody attaches itself to the spikes on the virus in order to prevent the virus from attaching to your body’s healthy cells and causing infection. These are the types of antibodies that COVID-19 vaccines aim to teach your body to make in order to protect against infection.
Natural infection with coronavirus will produce different antibodies. These antibodies can bind to not just the spike, but also to other viral proteins such as the nucleocapsid. Current COVID-19 vaccines in development do not lead to antibodies against the nucleocapsid protein.
The antibody tests currently in use will only detect the second type of antibody that is produced by a natural infection with coronavirus. As time goes on and more vaccine candidates are tested, however, new antibody tests might be developed that also detect antibodies that binds to the virus’s spikes. If this happens, it means you could get a positive antibody test result, even if you have never had been infected with the coronavirus. Health care providers may not interpret your test results correctly as an immune response to a vaccine; they may incorrectly see it as an indication of prior infection with coronavirus. Once an effective vaccine is found and widely administered to the public, testing technology will need to clearly distinguish between vaccine responses and infection.
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