What does IgM and IgG mean?

There are two key types of antibody that battle COVID-19. IgM antibodies appear at the start of infection to fight the virus. These usually disappear once the body has killed off most of the invading pathogen. As the body defends itself, another kind of longer-term antibody, called IgG, is produced to continue to mop up the invader and be prepared to defend against future exposures to the virus.