Covid-19 Myths: Does Natural Immunity End After 90 Days?

I first heard from a friend of the idea that being infected by Covid-19 doesn’t provide lasting immunity back in 2020.  I thought, “Wow, if this is true, the SARS-CoV-2 virus is different from anything we’ve seen before and will change what we know to be true about human immunology.”

Fast forward 1.5 years, and we now know the foundational principles of immunology are still true to this virus.  One such truth is that when we get infected with SARS-CoV-2, the natural immunity received does last.  

A peer-reviewed research paper from the journal Science in February 2021 looked at 51 people longitudinally over eight months. They concluded that 95% of subjects retained immune memory 6 months after infection and that circulating antibodies were not predictive of T cell memory.  This means that even if your antibodies go away over time, you’re still protected. 

95% of subjects retained immune memory 6 months after infection.

So where did this idea of losing your immunity after 90 days come from?  Much of this information comes from vignettes, such as this news story that looked at the reporter and the reporter’s friend who both looked at their antibody levels.  The reporter had antibodies, but the friend did not have antibodies after 90 days.  

To be fair, this story provides a decently balanced view of immunology by stating that antibody levels aren’t the whole story.  The main question of the report, however, was: “More than 11 million Americans (at the time) have contracted Covid-19.  The vast majority of them recovered thanks to antibodies.  But how long do antibodies actually last?”  

Circulating antibodies were not predictive of T cell memory.

Asking this question the way it’s asked is confusing because it implies that once the antibodies are undetectable, you do not have immunity.  This is not true.  The reason for this is best understood by explaining the two types of active immunity: humoral and cell-mediated immunity.  

Humoral immunity is mediated by antibodies. It shows a quick defense against pathogens and viruses trying to invade the host. These foreign microbes have antigens. The antibodies produced by the B-cells bind to the antigens and neutralize the microbes.  

Cell-mediated immunity is facilitated by the T-helper and cytotoxic T-cells. Cytokines secreted by the T- helper cells activate phagocytic cells which phagocytose the pathogens and kill them.

What is different about these two sides of our immunity is that TH cells participate in humoral  immunity while CD4+ and CD8+ cells participate in cell-mediated immunity.  What is similar about cell-medicate and humoral immunity is that both possess immunological memories, whereby your immune system can generate immune cells years after the original infection. 

This video from the University of Arizona mentions that people still have immunity to SARS-CoV-1 (the first SARS virus) 17 years later.  The researchers do a good job at looking at the data to determine that the antibodies lasted as long as the 6-7 months that they were examined.  

The same researcher put out a paper in the Journal of Immunology  on how “biologically implausible outcomes (e.g. you lose your antibodies after 90 days) were given equal weight as the principles set by decades of viral immunology.”  This paper is admittedly part review and part opinion, and it does an excellent job at how seemingly scientific but actually false information has made it to the mainstream conversation.  

In closing, one of my most used sentences over the last year has been: “Show me the paper.”  Show me where this idea that is being put forth as fact originated.  If there isn’t a paper, then we should be skeptical of the idea.  If there is a paper, then was it peer-reviewed?  Many journals are now pre-printing submitted articles that will go on to be rejected by the journal.   

The idea that people who have been infected by SARS-Cov-2 have natural immunity that lasts 90 days is false.  Studies show that antibodies alone last 6-8 months. From what we know of immunology, immunity derived from memory B-cells and memory T-cells last even longer.