On an individual level, an antibody test looks for antibodies in the blood. Your immune system makes antibody proteins to help fight infections. If you were exposed to COVID-19, an antibody test will show whether or not you’ve developed antibodies against SARS-CoV-2, the virus that causes COVID-19. An antibody test cannot tell you whether you have a current COVID-19 infection.
On a population level, antibody testing can give researchers a sense of how many people have been exposed to and infected by COVID-19. In the future, antibody testing may show whether someone has immunity against COVID-19, meaning that they cannot get infected again. If antibodies make people immune to COVID-19, it can help inform leaders and public health officials about whether the population has reached herd immunity. Herd immunity is when a large percentage of a population has become immune to COVID-19, which can protect those people who are not immune.