Currently, there are two types of tests for SARS-CoV-2,
which provide different kinds of information.
Diagnostic tests tell us if someone is currently infected. 
Antibody tests, also known as serology tests,
tell us if an individual was infected in the past
and has an immune response.
Serology testing does not detect the presence of the virus, 
but rather detects the antibodies that are, or were,
produced by the body in fighting the disease. 
Antibodies are proteins produced by the immune system
in response to an infection
 and are specific to that particular infection.
They are found in the liquid part of blood called
serum or plasma.
Immunoglobulin M, or IgM, is the first type of antibody produced
in response to an infection
and is detectable 4 to 7 days after an infection starts. 
IgM antibodies are short lived and their existence signals
a new infection is present.
Immunoglobulin G, or IgG, antibodies are produced
7 to 14 days after infection.
These antibodies can be detectable for weeks,
months and even years, 
depending upon the antigen and the individual.
IgG antibodies are usually sustained for a longer time
and may play a role in lasting immunity.
However, since we don’t know a lot about SARS-CoV-2,
as it’s a new virus,
we don’t know how immunity against this virus works.
Total assays, which are a combined IgG-IgM tests,
cannot distinguish between early IgM
and late IgG antibody responses.
As a result, total assays can’t reveal whether a person
has the IgG antibodies
that are needed for longerterm immunity,
or if they are currently infected.
For clinicians, knowing whether an individual has developed
SARS-CoV-2- specific IgG antibodies
could be critical to determining immunity.
An IgG-specific serology test reveals if someone had
COVID-19 in the past
and as a result has developed antibodies that are specific
to this virus.
The right type of serology test could help us understand
immunity against COVID19 at an individual and population level.
This can be a key tool to help us develop plans to reopen society.
