Are you protected against Covid-19 after infection or vaccination?
Do you know that in people aged 65+ the mRNA vaccines have a vaccine efficacy rate of between 61% to 95% with an average of 86%? So for people aged 65+, on average 14% are not protected even after full vaccination?
Now you can get peace of mind with the new Siemens RBD S1 antibody test. One simple blood draw at our office and you get results in a few days. You will know if you have neutralizing antibodies or not.
You may overestimate the level of protection and take fewer precautions placing you or a loved one at risk. Know if you indeed have neutralizing antibodies.
SARS-CoV-2 Spike Protein and Neutralizing Antibody
Targeting the right antibody can have a major impact on understanding patient immune response.
Why use a SARS-CoV-2 antibody assay that targets the receptor-binding domain (RBD) of the S1 spike protein?
- Cross-reactivity: Evidence showed an assay using the S1 RBD target did not cross-react with 4 common coronaviruses.
- S1 RBD antibodies have shown strong correlation to neutralization while evidence for neutralizing antibodies to the Nucleocapsid (N) protein is sparse.
vaccine response: The spike protein and particularly the RBD are the most
common target of vaccine designs.
All Antibodies Are Binding; Only a Subset Are Also Neutralizing
Humans produce antibodies against the spike protein and S1 RBD, as well as other viral proteins, but the key questions to answer are “Are they neutralizing antibodies, and can they protect you from reinfection?” Multiple studies indicate a primary role for neutralizing antibodies that target the spike protein of SARS-CoV-2, with antibodies to the S1 RBD estimated to comprise ~90% of neutralizing activity.2-5
Many vaccines are targeting the RBD, therefore antibody assays that measure antibodies to the RBD will likely prove valuable to assess an individual’s immune response to the vaccine.
Deep dive into the spike protein and neutralization
A common part of the immune response is for humans to neutralize or block the binding of the virus to the ACE2 receptor. If an antibody interferes with binding, you may have some level of protection. Different antibodies will target different proteins in the viral structure.
Spike (S1 and S2) Protein:
The S1 protein is the head of the spike protein and contains a receptor-binding domain (RBD). The S1 RBD is instrumental for allowing the SARS-CoV-2 virus to reproduce by attaching to and infecting host cells.6
The S2 protein is the stalk of the spike protein and allows the SARS-CoV-2 virus to remain fused to host cells.6
Nucleocapsid (N) Protein:
- The N protein is located inside of the capsid (the viral protein shell), along with RNA of SARS-CoV-2. This protein functions in the dispersal of genetic material during viral reproduction. The SARS-CoV-2 N protein is highly similar in structure to that of the SARS coronavirus (SARS-CoV).7
- Tests that detect antibodies to the N and S proteins (including the S1 RBD antigen) have been developed and indicate an immune response to infection.
Choice of target impacts the likelihood of cross-reactivity
Data indicates the likelihood of cross-reactivity is impacted by the choice of target in SARS-CoV-2 assays and may be more likely in assays that target both S1 and S2 or the N protein versus assays targeting just S1 or S1 RBD.8
- S1 RBD is highly specific for SARS-CoV-2 vs. other coronaviruses. Internal testing and an external study using the S1 RBD target showed that these assays did not cross react with the 4 very common coronaviruses.
- Evidence indicates that assays that target the N antigen may have cross reactivity with other coronaviruses, increasing the chances of false positive results and lower specificity.
This is the data that Moderna submitted to the FDA when requesting emergency approval.
Table 17 (page 29), you can see that in people aged 65+, the point estimate for
vaccine efficacy was 86.4% (range of 61.4 to 95.5%), compared
to an efficacy of 95.6% (range 90.6% to 97.9%) in people age 18 to
- This is still a very good efficacy, but note that it has dropped compared to a younger population. And…the aged 65+ group was most people aged 65-75.