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Serological COVID-19 spike protein antibody testing can identify individuals who have been exposed to the SARS-CoV-2 virus, regardless of symptom presentation, and quantify their personal immune response. We offer two testing options for the S-RBD antibody (spike protein receptor binding domain), the target of current COVID-19 vaccines due to the S-RBD antibodies ability to block the passage of COVID-19 to cells. The tests are optimized for pre and post vaccination testing, to deliver the information your patients need based on their individual circumstances.

When combined into a pre/post vaccination assessment, the COVID-19 Immune Response Panel and the COVID-19 Vaccine Response Screen provide clarity into not only when an individual should receive a vaccine, but the effectiveness of their body’s immune response to the inoculation.

What are S-RBD antibodies?

S-RBD stands for “spike protein receptor-binding domain.” The COVID-19 S-RBD binds to the ACE2 receptor and allows the virus access to the body’s cells. Higher levels of S-RBD antibodies have been shown to block or “neutralize” the COVID-19 virus from getting into cells and causing infection.

Typically, Individuals who have recovered from a COVID-19 viral infection usually have high levels of antibodies specific to S-RBD. The “neutralizing” ability of S-RBD antibodies is why all three of the Emergency Use Authorized (EUA) vaccines target the S-RBD, although they use different methods for getting the S-RBD protein information into the body.

Why measure S-RBD antibodies separately?

While human studies indicate that spike protein and nucleocapsid protein antibodies elevate in response to COVID-19 virus exposure, these antibodies are not as specific as the S-RBD antibodies for preventing COVID-19 infection (or re-infection) or for confirming post-vaccination status. After the virus infects the human body, it creates a large quantity of both “neutralizing” antibodies such as S-RBD and many nonspecific endogenous antibodies.

Although a general trend of post-infection increases in spike and nucleocapsid antibodies in association with increased S-RBD antibodies has been observed, measurement of the generalized antibodies is not always predictive of S-RBD status, particularly when the only stimulus is an S-RBD vaccine:

Why measure baseline and post-vaccine responses?

There are several good reasons to measure antibody status before and after a COVID-19 vaccination. Pre/post-vaccination assessment is the only way to be sure that a COVID-19 vaccination was effective. First, not everyone can mount an adequate antibody response to either COVID-19 infection or vaccination, and it is important to protect those that cannot make the needed antibodies.

Second, not everyone needs to be vaccinated immediately. Individuals with natural antibodies from a COVID-19 infection do not require immediate vaccination. After infection, a vaccination only becomes necessary when natural antibody levels begin to drop 3-6 months later. Serial testing can help determine when it’s the right time to vaccinate.

Finally, it is important to assess infection status prior to vaccination because the current Centers for Disease Control (CDC) guidelines advise against vaccination during an active COVID-19 infection. For this reason, two separate profiles are offered for the S-RBD antibody test: the COVID-19 Immune Response Panel and the COVID-19 Vaccine Response screen.

In essence, the best way to ensure your patients’ safety is by not assuming they are protected but rather assessing their status pre and post-vaccination to be certain. These two new testing options are valuable tools to confirm they have reached adequate protection from future COVID-19 exposures.

The COVID-19 Immune Response Panel measures both nucleocapsid (N-protein) and S-RBD antibodies. N-protein antibodies do not rise in response to COVID-19 S-RBD vaccinations. The combined serum IgM/IgG tests measure the body’s response to COVID-19 nucleocapsid (N) and spike protein receptor-binding domain (S-RBD) exposure. The N and S-RBD antibodies’ combination assay has a > 99% positive and negative predictive value 15 days after COVID-19 exposure. This test does not differentiate between IgM and IgG; studies indicate that joint testing is as or more reliable than individual IgM and IgG testing in confirming COVID-19 exposure.

The COVID-19 Vaccine Response Screen measures only the antibody response to the S-RBD protein. Once the baseline immune response has been established, this test can be used post-vaccination to evaluate immune status. The average time for seroconversion has been estimated at 2-3 weeks. However, the strongest antibody responses will likely be seen after the second vaccine dose 6-8 weeks after the first inoculation.