Good question and one we are all grappling with I think. We have a tool available, but aren’t quite sure if/how/when to use it.


·         About 80% of COVID-infected individuals develop IgG by day 14, and almost 100% develop it by day 30.

·         Some people with a new positive IgG still have detectable viral RNA by PCR in nasopharyngeal swabs.

·         The PCR can’t tell whether that viral RNA represents viable, replication-competent virus; so we have to assume a person who is PCR-positive may be still communicable.

·         We don’t yet know whether a positive IgG always represents neutralizing antibody and thus presumptive immunity.

o   One study, in preprint and not peer-reviewed, found that 2 macaques who had recovered from COVID-19 and developed IgG were rechallenged 28 days later with the same strain and remained asymptomatic.

o   Promising but a far cry from feeling comfortable that we can declare someone immune.

·         We don’t know how durable any immunity, if present, lasts.


So my personal take on this is:

·         IgG is not helpful in determining safety to RTW.

·         IgG may be helpful diagnostically, especially when an individual was not tested with PCR early in their illness course, and now appears to have late complications of COVID-19. The virus may be only replicating in the lower airway and nasal PCR could be negative. An IgM or IgG that was positive would help make the diagnosis.

·         If we find evidence of neutralizing antibodies and durable immunity, and we have a vaccine that is in short supply, the test could help us develop a vaccine prioritization.

·         If we find evidence of neutralizing antibodies and durable immunity, and we have another wave of hospitalized patients, IgG could help us identify HCP at lower risk, and this could be used in some sort of cohorting strategy.


My 2 cents only,




Melanie Swift, MD, MPH
Medical Director, Mayo Clinic Physician Health Center

Associate Medical Director, Occupational Health Service

Senior Associate Consultant

Assistant Professor of Medicine

Division of Preventive, Occupational, and Aerospace Medicine

Phone 507.284.2560

Mayo Clinic
200 First Street SW
Rochester, MN 55905


From: MCOH-EH [] On Behalf Of Thorne, Craig
Sent: Monday, April 20, 2020 12:01 PM
To: ''
Subject: [EXTERNAL] [MCOH-EH] Use COVID antibody results for return to work management?


Good afternoon everyone,


I am curious about current opinion on how you plan to use COVID antibody results for return to work management?  


At this point in the pandemic, we are not requiring home isolation for exposed essential HCWs regardless of their source of exposure.


Given all the literature about the uncertainties with COVID antibody testing, a discussion about this on this list serve could be interesting.


Thank you,


Craig Thorne


Craig D. Thorne, M.D., MPH, MBA
Chief Medical Director, Occupational Medicine and Business Health Services

Yale New Haven Health System

Cell: 203-687-5281




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