Antibodies detected in blood, bodily fluids, and tissue include IgA, IgG, and IgM. IgA and IgM are a response to acute infection. IgG antibodies take at least ten days to form and thereafter provide immunity against bacterial and viral infection. Saliva PCR testing for covid19 detects the presence of the covid19 spike protein, and not the type of antibodies present.
Saliva testing for the type of antibodies can be done, and would reveal if the patient has an active covid19 infection or past covid19 infection. Covid19 IgG antibodies can remain in saliva for extended periods of time after an acute infection, and would reveal the patient has had covid19 for at least ten days, or had covid19 in the past and recovered.
The lack of antibody testing in saliva for covid19 may explain why some people do not develop symptoms, or have more significant reactions to the covid19 vaccine—they have antibodies from prior covid19 infections.
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