There are five forms of antibodies that the human body makes. There are two forms that are relevant for COVID 19, Igm and IgG.
Igm is a big molecule, which is the first molecule that your body makes when you are exposed to a particular antigen or virus. This is an acute phase type of antibody.
IgG is a long-term antibody that has memory for your immune system and also protects you long-term. The actual length of long-term protection is not known.
Typically, when you have antibody testing, you are tested for both Igm and IgG. These tests are not perfect. If someone tests positive for Igm but not IgG, we’re not sure if they are protected.
If someone has no Igm antibodies and lots of IgG antibodies, they’re likely protected due to the long-term memory of IgG.
The length of time the antibodies remain detectable following an infection is not known.