Can COVID-19 vaccines alter or weaken my existing immune response against other viruses?

Biology/Immunity Vaccines

A. No. COVID-19 vaccines do not affect existing immune cells or antibodies that you have made against other viruses.

Nor will it prevent you from making an immune response to another virus when you encounter it.

👉 TL;DR: Our immune system is designed for IMMENSE flexibility to be able to respond to thousands of pathogens that we might encounter throughout our lives! COVID-19 vaccines induce an immune response to the spike protein of SARS-CoV-2. A small fraction of immune cells will develop a response to the vaccine. Other immune cells that recognize other viruses, either from previous infections or vaccinations are not affected by COVID-19 vaccines and will continue to protect us against a variety of viruses that we have previously encountered or been vaccinated against. We also continue to have immune cells that have not committed to responding to a specific vaccine and are able to respond to new vaccines or infections. Depending on the infections we encounter, the specific pool of immune cells that can respond to the infection expands rapidly, deals with the infection and contracts back into a smaller pool of ‘memory’ immune cells.

❓How does the immune system respond to vaccination? When we are vaccinated, our immune system is shown bits of a virus. The various cells of the immune system learn to recognize them as foreign to our bodies.

🌟B cells (the cells that make antibodies), learn the specific shape of the bits of virus and make antibodies that can neutralize the specific virus or block its entry into cells.

🌟 T cells learn to recognize specific stretches of the viral protein and retain this memory so that they are able to destroy cells infected with that specific virus. In doing so, they clear the virus from our bodies.

Not ALL of our immune cells will respond to a specific vaccine. Of the millions of immune cells in our bodies, only a fraction will have the correct type of ‘receptor’ on their surface that can recognize the vaccine – similar to a lock-and-key. The cells that are a good fit (key) for the vaccine (lock) multiply rapidly after vaccination, especially after the second dose (booster). A few weeks-months later, these cells contract into a smaller pool of ‘memory’ cells. These cells can be called upon to battle the virus if we ever encounter it. This is how all vaccines work to protect us from infections.

❓Do we have a similar ‘pool of cells’ for other viruses? Normal adults have between 1000 to 4500 ‘lymphocytes’ (T and B cells) per MICROLITER of blood (that’s an extremely tiny drop of blood).

Considering that we have 1.2 to 1.5 gallons (4.5 to 5.5 liters) of blood, that’s a LOT of lymphocytes! Only a very small fraction of these cells will have the right configuration to recognize the COVID-19 vaccine. Those cells will eventually form a small pool of ‘long term memory’ T and B cells. Similarly, we have pools of lymphocytes that recognize the various vaccines we have received over the years and other pathogens we have encountered during our lives. These pools of memory cells can be called upon to combat specific viral infections (sort of like different units of a standing army!).

➡️ Although we have a huge variety of memory cells, we also have NAIVE cells – these are cells that have not yet learned to recognize a vaccine or a virus. They are extremely important for our protection against NEW viruses that we have not seen previously. These naive cells have the ability to learn. When we encounter a new virus, these naive cells can learn to make a specific response. They then become a new pool of memory cells specific to this new virus. Babies have a large number of naive cells that are eager to learn, however their support system for immune learning is not mature enough. As we grow older, we have a larger proportion of memory cells from all the vaccines we have received and the viruses (or other infections) that we have encountered in our lifetime, but we have fewer naive cells. This is why it can be harder to make a strong immune response to vaccines or infection in the very young and the very old. In fact, this is also why some vaccines are formulated differently for the very young and the very old, such that their immune systems receive some extra help.

➡️ In some instances, a vaccine can actually help preserve immune memory to other infections, whereas infection with the same virus may erase immune memory to other infections. Researchers have shown that infection with the measles virus can wipe out previous immune memory to other viruses (e.g.; chickenpox virus). While the exact mechanism is as yet not clear, it is possible that the severe inflammatory response induced by infection has negative effects on the immune system as a whole. The measles vaccine not only prevents measles but it might give the whole immune system a general boost and help retain immune memory to other infections.

❓Could SARS-CoV-2 infection result in a similar decrease in immune memory? We know that lymphocyte numbers drop in patients with severe COVID-19. While we do not have specific data regarding the effect of COVID-19 on pools of memory cells, it is possible that a significant drop in lymphocyte numbers could damage our existing pools of memory cells. Therefore, getting vaccinated against COVID-19 may provide additional benefits as the vaccine does not reduce our lymphocyte populations.

👍🏽 BOTTOM LINE: COVID-19 vaccines do not reduce your immune response to previous vaccinations or to new viral infections.

Stay safe!
Those Nerdy Girls.

ℹ️ Further information:

How does immunological memory develop?

Animation: Developing immunological memory

COVID-19 Immunology 101 for Non-immunologists by Akiko Iwasaki, Ph.D.

Immunological memory


How the immune system works

Measles virus may deplete immune memory


COVID-19 leads to low lymphocyte counts:


National Center for Biotechnology Information

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