When a new virus invades the human body, the immune system leaps into action. First to the scene are antibody molecules of a type called immunoglobulin m (IGM). These bind with proteins on a virus’s surface, disabling it and marking it for destruction by cells called macrophages. A few days later the system produces a second type of antibody, immunoglobulin g (IGG), to continue the fight. IGMs are short-lived. They stick around in the bloodstream for three or four weeks before disappearing. The Economist writes that IGGs, however, are the basis for a much longer-term form of immunity. This can last for many years, or even a lifetime.
Kits that test for these two types of antibodies when they have been raised specifically by sars-cov-2 should soon become available.