SARS-CoV-2 Viral Antibody Tests

Are you immune?

Background. While the virus that causes illness we call COVID-19 is NEW, there is not much reason to believe that it behaves much differently from other respiratory viruses (including the other coronaviruses that cause respiratory illnesses). This virus is known as SARS-CoV-19.

Viruses (which must replicate within a host’s cells in order to acquire all the components it needs to reproduce) are made of many different proteins.  These proteins serve as “antigens” to which our immune system responds, hopefully to build our immunity to help clear the infection and resistance to prevent a renewed infection at a later time.

Natural Infection. The response to the antigens of invading organisms in humans and animals is of several types, and leads to the development of humoral antibodies and also to cellular immune responses (involving selected types of white cells such as T-cells, B-cells, and so on). 

Immunization. Besides responding to active infections we respond to antigens from the viruses if they are injected beneath our skin, as in immunization. Without a doubt, immunization has led to arguably the most important single advance in public health and preventive medicine that we have ever seen. 

Usually people with natural infection get as good or better immunity from that natural infection (as they respond to many antigens of the whole whole virus) than others do from a vaccine composed of incomplete viral components. The current Pfizer and Moderna vaccines commonly available in the US contain antigens to the Spike proteins on the surface of the virus, and not the entire array of viral antigens (see image of virus).

Measuring Immunity. Although natural infections and immunizations can possibly lead to the development of  both humoral immunity and cellular immunity, cellular immunity is often quite difficult to estimate using ordinary laboratory tests on our blood. However, humoral antibodies are much easier to measure, and in fact we can easily see a rise in titer of these antibodies within 3-4 weeks of the onset of infection. 

Natural infections. The best diagnosis of such infections in a clinic and when counting cases in an epidemic in epidemics involves creating a decent case definition, which includes:

1.  A presence of the correct and most common symptom complex associated with illness,
2.  A culture or antigen test for the agent, and 
3.  At least a four-fold increase in antibody titer over 3-4 weeks or more following the onset of illness (for example a rise from 1:4 to 1:16).

Antibodies associated with immunoglobulin M (IgM) usually rise first and then are joined by those associated with IgG (as IgM antibodies gradually wane). Sometimes having tests on both these two, on a single serum, is helpful in estimating time since infection if we do not have paired sera. However with SARS their timing is fairly closely tied together, so that measuring one, such as IgG is sufficient.

Duration of Immunity. We hope (after exposure to natural infection or immunization) for life-long immunity to these antigens. Often that is achieved.  However, as humoral and cellular immunity decays, reinfection becomes more likely if re-exposure occurs. There are special situations where viruses undergo gradual antigenic drift, and as in influenza A and B, the vaccine components are updated each year in an attempt to provide the best vaccine components. Other infections and vaccines seem to offer lifetime protection.

What can we do? If you watch cable news or follow news apps and social media online, you probably realize that the current COVID-19 pandemic has, from the beginning, been highly politicized. Even our most respected authorities and agencies seem barely aware of what to do. Certainly you are following along with the issue of vaccine mandates.  It seems surprising that even those with natural infection to the SARS-CoV-2 virus are expected to require vaccination, especially in light of potential reactions in those folks.

So, for your own purposes, you might wonder if you are immune. Although we focus on the prevention and minimization of arterioschlerotic cardiovascular disase for obvious reasons, we cannot help but wonder why no one is commonly promoting SARS-CoV-2 antibody testing for individuals since it is readily available. So for now, our members can get a decent estimate of their humoral antibody status by performing several antibody tests at their local laboratory.

What will the results tell me? Antibody tests can show whether or not you appear to have developed antibodies to COVID-19 after exposure or vaccination. This test cannot tell you if you have an active infection. If you suspect you have COVID-19, follow up with your healthcare provider about getting a PCR nasal swab test. This blood test will not let you know if you are currently sick with SARS-Cov-2 virus, and should not be used to determine the actual precise level of immunity you have. 

 Here is a summary of the currently available tests:

What is the difference in the spike and nucleocapsid proteins? Antibodies against the SARS-CoV-2 viral spike protein have been shown to have neutralizing effects. Current vaccines have been developed to elicit antibodies to the spike protein. There are both semi-quantitative and qualitative options for testing for spike protein antibodies.

Which tests do you provide? We are currently recommending the SARS-CoV-2 Antibodies (Nucleocapsid) and the SARS-CoV-2 Antibodies (IgG, Spike). The reason for this is that it allows us to determine if you have antibodies, and even better whether your antibodies are likely to be from natural infection or from vaccination alone (or both).

For example:

Will we discuss my results? Yes, definitely. As part of our programs we discuss your lab results with you on a HIPAA-compliant Zoom session, or or by telephone. If you review the Table shown below, you will see the possibilities.

If you have no antibodies, it suggests that you have not had an antibody response from the infection or a vaccination. Depending on which of your tests are positive, we can induce the following: With previous natural infection you should have evidence of both Nucleocapsid Antibody and IgG Spike Protein Antibody. If you have had vaccination alone but no natural infection you should have IgG Spike Protein only.

Disclaimer. Like most things dealing with COVID, these tests have not been FDA cleared or approved. However the tests have been authorized by the FDA under an emergency use authorization for use by authorized laboratories such as those we use.