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Are We Immune to COVID-19 if We've Been Exposed?

We can now test for T-cell immunity, which may indicate long-term immunity.

Key points

  • Antibodies usually take weeks to build up and last a few months. Testing for them can make it difficult to find out if someone has been exposed.
  • T-cell immunity to Covid-19 is expected to last several years, and Covid variants do not seem to elude T cells.
  • About 95 percent of people have immunity to the coronavirus up to at least eight months after infection, according to research.
  • For those who wish to know if they were ever exposed and may have immunity, memory T-cell testing is now available.

The immune system is broken down simply into two parts:

  1. The innate immune system
  2. The adaptive immune system

The innate immune system is composed of white blood cells such as natural killer cells (Nk cells), basophils, dendritic cells, eosinophils, and more that act as "first responders" to early infectious agents throughout the body. From there, they present their "findings" to our T cells. Think of T cells as officers in the military that are presented with information from the battleground and they make the call of how our immune system should respond. This information presents to our adaptive immune system and includes antibodies, but also memory T cells; both create longer-lasting immunity against invaders in case we are exposed to them again in the future.

The Difference Between T Cells and Antibodies

There are important differences between antibodies and T cells:

Once exposed to Covid, antibodies actually take most people upwards of three to four weeks to be created, then last only three to six months. T-cell immunity occurs quicker and is why it is rare to see Covid reinfection, as the CDC states, and further explains how so many people recover from Covid before antibodies even form.

The public focus on antibodies has actually made it difficult for many people to find out if they were ever exposed. Using antibody testing to check prior exposure means some people may not be positive yet. This has been the dilemma, until now.

T-cell immunity has already shown to last up to 17 years , according to the data from the original SARS-Cov-1 virus which is very similar in structure to the Covid virus. In fact, experts agree there is no reason to expect T-cell immunity to be any shorter in Sars-Cov-2, a.k.a. Covid-19, providing better long-term immunity.

Recent research backs this up with Covid-19, as a study revealed about 95% of people retained immune memory up to at least eight months, and durable immune responses are suspected to last even longer.

Such testing and decisions should be discussed with your doctor for appropriate risk-benefit analysis and informed decision making, as Governor Ron DeSantis points out, particularly for those under 65. Furthermore, recent studies show that our T cells are not eluded by recent variants which is very promising as well.

What Does This Mean for All of Us?

Imagine how many people have been exposed to Covid-19 over the past year, given that 45% of people are asymptomatic , or don't show symptoms. The great news is that now there are FDA-authorized T-cell tests available in order to reveal if you've been exposed. Companies now offer these tests to the public and to physicians to see if someone has been exposed and potentially has long-lasting T-cell immunity.

This may provide key answers to people but also to several companies looking to remain operational with less liability. The more it is acknowledged, the more our politicians may act with this new information. This couldn’t come at a more pivotal time as most high-risk people have already been vaccinated; this could in fact be an important piece to helping individuals and also countries return to normal.

References

https://www.cdc.gov/coronavirus/2019-ncov/your-health/reinfection.html

https://www.nature.com/articles/s41577-020-00436-4

https://science.sciencemag.org/content/371/6529/eabf4063

https://pubmed.ncbi.nlm.nih.gov/32668444/

https://www.nature.com/articles/s41564-020-00813-8

www.T-detect.com

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