In our previous update we discussed some of the pitfalls and cautions related to antibody testing, in particular the caution against using testing that is not reliable, and caution against making assumptions about the nature of the immunity.
Questions continue to come in from those who have been tested with reliable tests,and less reliable tests.When a test is less reliable,the answers are a guess. Even with a good test there remain persistent issues about how to interpret the results, and other general antibody related questions. We will attempt to address some of these below, with the disclaimer that applying principles learned from other viral infections may not apply to this novel coronavirus (SAR-CoV-19) which causes the COVID-19 illness.
Q: Who should be getting an antibody test?
A: We are recommending that adults (>20 years old) primarily based in Crown Heights get tested for the presence of antibodies. For those that have been in isolation due to their high risk status, we do not recommend they leave isolation for the purpose of testing at this time, due to the risk involved.
Q: Where should one be getting tested?
A: Many will be getting tested at the upcoming Mayo Clinic drive (if they’ve registered). Alternatively, make up a time with your primary care provider to arrange for a blood draw if they are making that available through reliable tests. Remember a bad test is worse than no test.
Those that use the Crown Heights Mayo Clinic drive need to be aware that this is for the purpose of getting plasma from donors to treat other patients who are acutely ill, and in order to find donors, testing of antibodies must first be done. Those tested will receive their results.
Q: When should one get tested?
A: As a general rule only those that have recovered from the virus should get tested, and people should check with whoever is administering the test whether they have stricter criteria. Antibodies usually develop by the 3rd week after getting ill.(A person who is still ill must NOT present to a “testing drive”). There is no emergency to get tested, if not planning to donate plasma, and for now there will not be any immediate change in “status” or recommendations on the basis of testing.
Q: What does a positive antibody test mean to me?
A: Some tests will just be reported as positive or negative. Others are quantitative and result in a numerical value (“titers”). If you have a positive test with a high value, then you are a suitable plasma donor. We assume that a high titer value will confer some immunological advantage, although this is still being studied.
A test that just gives a positive/negative result does not define the amount of antibody present. Having a positive test that is reliable will in almost all cases mean that one has been exposed to the virus, and that they are less likely to become reinfected in the short term. How this translates to long term immunity is not clear at this time.
Although most people with a positive antibody response will be less likely to be infectious, there are still some individuals who persist in carrying viral particles in the upper airway and are tested positive for antibodies. Whether or not these individuals remain infectious is still a question,and they should be careful to wear a mask in public.
Q: What does a negative antibody test mean to me?
A: Assuming a reliable test, a negative antibody test may either mean that you did not have the illness (although most adults know that they were ill with COVID) or that you have not mounted the kind of immune response measured by the test. There are many subtypes of antibody and memory banks in the immune system where the antibodies may be stored that we are not measuring. How this impacts future encounters (G-d forbid) with the virus is unclear at this time.
If you’ve had COVID symptoms, and a negative test: You may not have mounted an immune response, or your response is not measurable, but present, or you did not have the disease. We don’t exactly know the answer to that, and we assume that you remain at a higher risk than those with measurable antibodies.
If you have NOT had COVID symptoms, and your antibody test is negative: Be extra careful, you are at the HIGHEST risk of still contracting illness from a stray case.
Q: Should I get a nasal swab to see if I am carrying the virus?
A: If you are well, there is no reason to get a nasal swab done. Those who have “minor'' persistent symptoms, but are otherwise quite well, and back to themselves should likewise not get swabbed. There is a significant group of individuals who remain with positive nasal swabs weeks after their recovery. They are “likely” not infectious any longer, and the positive test does not necessarily represent an actively infectious virus. Those with persistently positive swabs, should avoid contact with vulnerable individuals (particularly the elderly) and continue to be careful with mask usage.
However there is also a group of patients who are still ill with multiple symptoms weeks after onset. They should see their health care provider, and be evaluated including being tested for the presence of virus in their upper airway (swabbed). A positive test in these individuals, given our current knowledge would possibly indicate continued infectivity. They should continue isolation, and repeat swab within 2 weeks.
If you have recently developed symptoms of the illness, you MUST see your healthcare provider (please inform the office prior to the visit that you are ill and possibly infectious) and you must be tested with a nasal swab-and quarantined along with close contacts until the situation is clarified.
Q: If my blood antibody test is positive now, will it persist, and for how long?
A: At this time we cannot answer that question. However for public health purposes it would be valuable for everyone with a positive test to repeat their test sometime in the future, and we will update with recommendations and guidelines as they come out.