I’ve never had Covid. Does that mean I’m immune?

The simple answer is maybe, but not likely.

Many people here in the United States have some immunity to Covid due to prior exposure to Sars-Cov-2, vaccination to Covid, or a combination of the two. There are people who have been in close contact with those with Covid, have not masked, or are not vaccinated, but have no history of Covid-related illness.

Initially, we had limited testing, and thus could not confirm all who were Covid positive. As testing became more available, they noted the variants such as omicron and delta presented people with milder illness. Perhaps this was likely secondary to many individuals being vaccinated during these variants’ appearance.

Some “sick” individuals may assume their symptoms are cold or allergy-related and choose not to test. Although these individuals would have developed Covid antibodies, they may have low viral loads making at-home tests incapable of detection.

Causes of mild or no Covid symptoms

These could be due to:

1. natural immunity (could have a genetic component);
2. cross protection from another illness such as a respiratory infection; or
3. prior exposure to Covid, which then protects against future infections.

We have seen the generalized variants, alpha, delta, mu and omicron. Infection with any of the listed does not guarantee protection from a variant by another name. For most, vaccination or exposure to Covid only provides partial or temporary immunity. It has been reported that immunity may last as long as eight months after Covid infection.

Post-Covid infection the body responds with antibody production as well as increased production of B cells and T cells to attack the virus. Those that are immunocompromised or even pregnant may not mount an antibody response.  

Blood tests for antibodies were used early in the pandemic to see if these at-risk individuals had prior exposure to Covid, but not necessarily a gauge for immunity. Their exposure status was useful as they are at high risk for negative outcomes post-SARS-CoV-2 exposure.   

Immune status for all individuals would be useful in determining what kind of precautions any individual may need to take regarding Covid, or even if a booster is needed.

New lab tests for immunity 

The existing antibody “immunity” test is expensive, time consuming, and doesn’t quantify the level of immunity. This explains the FDA’s position on immunity testing for Covid.

As of February 2022 the FDA has stated: “Currently authorized SARS-CoV-2 antibody tests have not been evaluated to assess the level of protection provided by an immune response to COVID-19 vaccination.”

The FDA position is taken as they believe an incorrectly interpreted antibody test has the potential of influencing people into taking fewer precautions against SARS-CoV-2 exposure, which can increase their risk of infection and may result in the increased spread of SARS-CoV-2.

Within the past month, advances in analyzing the antibodies (IgM and IgG) to the receptor binding domain (RBD) of SARS-CoV-2 have occurred. These antibodies block the SARS-CoV-2 RBD from binding to ACE2, the human receptor that the virus uses to infect cells. Specifically, a test was developed that can detect the presence of antibodies that block the SARS-CoV-2 RBD from binding to ACE2.

SARS-CoV-2 and other viruses have shown a strong correlation between the amount of neutralizing antibody circulating in an individual’s bloodstream and their likelihood of infection.

Since our response to SARS-COV-2 is also mediated by T cells, measuring T cell activation is critical to assess the full extent of a person’s immunity. A study done June 2022 demonstrated that T cell measures may be more useful than antibody titers (amounts) for level of immunity. 

This is essential as variants like Omicron evade most of the neutralizing ability of antibodies.  In this way, tests that can measure T cells may provide more evidence of immunity toward emerging variants.

In summary, it is unlikely that an immunity test that all scientists and governing agencies agree is useful will be available immediately. As a result, we should continue to be mindful and take precautions as one sees fit in regards to SARS-CoV-2 exposure. 

Hopefully, as vaccines continue to be refined, we may have lasting immunity post-vaccination in the future as well as a reliable way to assess if we are immune.