Does Preexisting Immunity Mean that SARS-CoV-2 Has Already Been with Us?

I am inclined to go with the theory that prior infection with other coronaviruses gave the immunity observed. I had a lot of cold/flu viruses early in life and have had no sign of infection with Covid despite being elderly and despite being in contact with infected people

A preexisting immune response can be seen in adults who have not been exposed to the SARS-CoV-2 virus. Dr. Paul Alexander, COVID-19 Consultant Researcher in Evidence-Based Medicine, quoted a research study in his Substack blog titled “Making the case that COVID-19 virus was NEVER ever ‘novel’ or new, it was circulating for many years and we had some level of cross-reactive immunity.” According to research, it is more likely that preexisting immunity represents a form of cross-reactive immunity instead of meaning that SARS-CoV-2 was already with us before the pandemic.

Playing a very important role in adaptive immunity, T cells and B cells are formed as a result of encountering a pathogen. With these soldiers, our immune systems produce antibodies that attack foreign substances to protect our bodies from infections and learn how to fight better and faster for the next encounter.

This system works in the same way following exposure to the SARS-CoV-2 virus. However, it has been revealed in the intensive research on this subject that there is no need for exposure to SARS-CoV-2 for these cells to form. In some individuals, preexisting T and B cells can emerge without exposure to the virus.

Current Study and Main Findings

In 2021, a study published in JCI Insight was conducted by Abdelilah Majdoubi, PhD. from BC Children’s Hospital Research Institute and colleagues to investigate the extent of the preformed immune response to SARS-CoV-2 in the Canadian adult population. They also investigated whether this immune response could be explained by existing coronaviruses or direct exposure to the SARS-CoV-2 virus.

The research was funded by the BC Children’s Hospital Foundation, the Intramural Research Program of the Vaccine Research Center (VRC) at the National Institute of Allergy and Infectious Diseases (NIAID), National Institutes of Health (NIH) and also in part by the Canadian government via its COVID-19 Immunity Task Force.

This study revealed that most adults in the Canadian population show antibody reactivity to SARS-CoV-2 antigens. However, the authors concluded that it is highly unlikely that this immune response was formed from direct exposure to the SARS-CoV-2 virus. There were relatively low cases of COVID-19 after the first wave in the British Columbia region. This greatly reduces the likelihood of a pre-existing and asymptomatic circulation of COVID-19. Also, pre-pandemic sera from adults and sera from infants younger than one-year-old revealed a similar antibody reactivity, which bolsters arguments for cross-reactivity.

Possible Sources of Cross-Reactive Immunity

If COVID-19 was not circulating before the pandemic, then what is causing this immune response? It is widely known that a strong immune reaction, in the form of antibodies or T-cell responses, occurs when the virus itself is encountered or by vaccination. Interestingly, upon exposure to cross-reactive antigens from different viruses, bacteria, vaccines, and even certain food proteins, antibodies can also be formed to create an immune response.

It is hypothesized that exposure to coronaviruses predating COVID-19, particularly common cold coronaviruses, may have created reactive T-cell responses against the SARS-CoV-2 virus.

Implications and Conclusion

The fact that immunity has pre-formed in individuals who have not been infected with COVID-19 does not necessarily mean that SARS-CoV-2 is not a newly emerged virus. However, these findings still have important implications.

The presence of cross-reactive antibodies in some people and their absence in others may cause differences in the severity of the disease in different people. The heterogeneity of COVID-19 disease, which is more severe in some people and milder in others, may be a result of cross-reactive immunity.

It is also important to note that pre-existing immunity does not always provide a protection advantage. More research is needed to investigate the extent to which this cross-reactive immunity provides protection against disease.


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