An Expert Q&A on COVID Antibody Testing

September 4, 2020
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In recent weeks, the value and nature of antibody (Ab) testing’s role in the pandemic has come into focus, especially in the arena of validating potential treatments such as convalescent plasma. With antibody testing playing a more focal role, we sat with two industry experts to answer a few of the most common questions submitted by the more than 1,000 registrants of our recent webinar, “Demystifying COVID-19 Antibody Testing.”

Our two experts, Dr. Jerry Yeo, PhD, DABCC, FAACC of the University of Chicago, and Dr. Stephen Rawlings, MD, PhD of the University of California, San Diego, weigh in with their expertise below.

Q: Because antibodies don’t appear until a week or so after symptom onset, it seems useless for contact tracing, isolation and quarantine. What value does Ab testing have for control of pandemic?

A: Dr. Yeo – While the utility of anti-SARS-CoV-2 Ab is somewhat less sensitive in detecting exposure in the first week after symptoms onset, I would say its use is limited but not necessarily “useless” for potential use as a tool for contact tracing.  This is because a large number of infected individuals may either be asymptomatic, pre-symptomatic or mildly symptomatic and thus are unlikely to seek the Covid-19 PCR testing right away. In addition, there’s still a current shortage of PCR testing reagents/supplies and delayed turnaround time for results is not uncommon.  Thus in the situation where such an individual who suspects later that they might have been exposed previously, an antibody test used with the proper clinical context, can be helpful to ascertain exposure to Covid-19, and thereby facilitate contact tracing of others who might have come into contact with this particular individual.  While antibody testing cannot be used for diagnosis of acute infection, it can definitely be used as an additional test to confirm exposure in late-presenting individuals. Truvian’s lab-accurate antibody test will aid in providing key data that will allow us to better estimate the number of people previously infected to inform public health measures, and may assist in the broader availability of treatments such as convalescent plasma, which requires blood donations from individuals previously exposed to COVID-19.

Q: How long can antibodies be found in the COVID-19 patients?

A: Dr Rawlings – This is a key question that we are seeking to answer with ongoing studies. Obviously, with a virus that has only been infecting humans for perhaps nine months or so, we do not know the long-term stability of antibodies. Other viruses can induce antibody responses that last for years. There is also the issue of “detectable” antibodies versus “effective” antibodies. It is possible antibody levels may wane to a point that they no longer protect the individual from disease but are still detectable in sensitive lab assays. This will all need to be studied going forward to determine longevity of immune protection from re-infection. From our initial studies, it appears the vast majority of individuals maintain antibody responses for at least 5-6 months, but this is again limited solely by the time that our study has been open.

Q: Is there a known or presumptive correlation between presence of strong neutralizing Ab’s in the blood and susceptibility of reinfection?

A: Dr. Rawlings – This will also be a key question in predicting the course of the pandemic and it will require long-term studies of convalescent patients to determine their risk of becoming re-infected. Our understanding of the immune system and other pathogens would suggest a direct correlation between titer of neutralizing antibodies and protection from infection, but if there are other mechanisms to protect individuals from infection besides the humoral (antibody) defenses (e.g. T-cells), then there could be individuals with low neutralizing antibody titers who are still well protected. The data so far suggest re-infection at 3-6 months post-initial infection is rare, but it will be important to follow individuals with both strong and weak neutralizing antibodies to determine their risk of re-infection. These studies are ongoing.

Q: Regarding correlation with Nab, is there a view on whether S protein antigen vs NP antigen-based tests will be any different? 

A: Dr. Yeo – There are now emerging work that appears to suggest that spike RBD antigen-based antibody test correlates better to neutralizing Abs test, even though there is still statistically significant correlation between nucleocapsid antigen-based Ab test. Given that Easy Check uses both spike RBD and NP antigens cocktail, the antibodies (IgM and IgG) detected should correlate well with Nab test, and potentially could be used as a surrogate test to indicate the presence of Nab. Of course, a study needs to be performed with the Easy Check vs Nab to show just such a correlation exists.

To view the full webinar and hear more from Dr. Yeo and Dr. Rawlings regarding the value, utility and limitations of COVID-19 antibody testing, click here.