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March 26, 2021
Humoral Responses to COVID-19
Kamran Kadkhoda, Ph.D., SM(ASCP), D(ABMM), D(ABMLI)
Medical Director, Immunopathology Lab
Main Campus-Cleveland Clinic, Cleveland, OH
Answers to Additional Questions from Viewers:
- Can you please repeat the information on the vaccines with lower efficacy and the herd immunity claim?
- Also, for those vaccines with lower efficacy, is it worth it to measure serology?
No, for the reasons explained throughout the talk including lack of an established COP, there’s no need for doing serology routinely by clinical labs but instead usually done in the research setting and by vaccine makers to fine-tune/improve their vaccines. This is done yearly for flu vaccines. Also remember efficacy is a clinical end point and is more important than just one lab test measurement i.e., serology. Furthermore FDA does not require any pre-/post-vaccination serology.
- How are children &/or adults on immunoglobin supplement (IV or s/c) monitored for SARS-CoV-2 Abs?
There are no guidelines for such groups at this point but that being said, depending on the population the IVIG is procured from, it may contain Anti-SARS-CoV-2 Ab interfering with serology. Also IVIG in general can interfere non-specifically with any serological assays. Essentially these patients has some degree of humoral deficiency (such as in CVID) and doing serology in general be it post-infection or post-vaccination is fraught with ambiguity.
- What about SARS-COV-2 Ag based serological Assay? are they also not good for COVID-19 Diagnostic?
Not relevant to this talk as we talked serology which is indirect detection and Ag is direct detection but just to say Ag testing is much less sensitive and a bit less specific than RNA testing so should not be routinely attempted unless RNA testing is not feasible (economically or logistically) and once done, CDC algorithms must be followed.
- In a lot of the studies you quoted early, the target antigen of the antibody test wasn’t specified. In your later slides you showed the relative stats for the different target antigens. Has there been any meta analysis of the early data comparing the overall NC assay performance characteristics to the overall spike or RBD results?
The purpose here was not to discuss which kit performs better; the elephant in the room is serology as a whole is not a suitable option for reasons I tried to explain but yes, there are differences between different kits and targets and there are such publications on their performance but again not done the proper way I highlighted namely by using PRNT. The common way has become testing a group of pre-pandemic samples (convenience testing) and call it specificity. On the sensitivity side things are done much better but still low overall sensitivity making this useless in routine diagnostics. On very general average though, NC/NP-based assays perform less sensitive and specific than spike-based ones that being said there’s a great deal of heterogeneity among patients and different studies.
- Since serology appears not to predict protection, any idea what labs should be doing to close this gap?
Not much; keep abreast of knowledge in the field and wait until COP is known and then we’ll know how to proceed from there. It is more of a research thing to close that gap than clinical labs routinely get involved and offer the tests in a hope that the results may or may not be useful, this is the reverse approach. Good example is flu vaccine for which we don’t do serology or we’re not obliged to close any gaps, so we should stay tuned!