I got my first Covid vaccine yesterday. I have an appointment for the second dose in three weeks. Time will tell whether this turns into an annual ritual. I hope not, but as this coronavirus has spread throughout the world, and variants have appeared over the last year, it is possible that variants will continue to circulate indefinitely.
This vaccine is different. It doesn't contain antigens from the virus, but mRNA strands. Once injected, these RNA strands should be absorbed by cells. The RNA will bind to ribosomes in the cytoplasm of these cells, and copies of proteins will be made. I don't know how the copies of the protein get out of the cells, where phagocytes can find them, but I'm guessing that is supposed to happen.
Once the cells start releasing the proteins, and the phagocytes start engulfing them, those phagocytes can carry them to my lymph nodes, and search for lymphocytes that have antigen receptors that recognize these proteins as antigens. Once that happens, my adaptive immune response can kick in, and I can start making antibodies and cytotoxic T cells, which would then be available to fight off the virus if I am ever exposed.
Because this process is different, the timing of events, including reaction to the virus, could be quite different from a traditional vaccine. I should take a few hours for protein synthesis to make enough product to change things. Of course, starting with mRNA rather than transcription will shorten that process by quite a bit, as neither the synthesis of the RNA nor the transport of RNA out of the nucleus has to happen. But with a traditional vaccine, the foreign antigens are immediately present, so inflammation starts with injection. With the RNA vaccine, the immediate reaction will be to the needle stick and the pressure of the fluid, but not so much foreign macromolecules. I don't know how the tissue, or phagocytes, will react to extracellular RNA. Since research has clearly shown that extracellular RNA is absorbed, that must not be too strange or rare a phenomenon. There is a mechanism for RNA to be absorbed, so extracellular RNA must already be normal, at least sometimes.
I don't know how long it takes with this vaccine before I have any protection from the virus. Certainly not today. With a traditional vaccine, it take at least a week, and more like ten days before antibodies appear, with a peak in production around fourteen to twenty-one days. Then the immune system is ready for a secondary immune response, which is faster and larger than the primary response. A major part of both is the production of memory cells, both memory B cells and memory T cells, which provide the longer term protection.
As this is the first RNA vaccine in widespread use, I expect there is a lot of research being done to track these effects. This is also a first test for a vaccine for a coronavirus, I think. Coronaviruses seem to provoke rather weak and short-lived immune responses, from what I have read. There are four strains that cause cold-like symptoms, but no immunity, so a person can repeatedly get the same cold from them. The coronavirus responsible for SARS, which had its notorious outbreak back in '02 in China, caused antibody production which lasted about three years, in at least one study. A vaccine for that virus was developed, but never tested in clinical trials, because it wasn't ready until 2016, and no one wanted to pay for the clinical trials by then, because no one had had the virus for over a decade. That was a missed opportunity.
I think, once we more or less get past this pandemic, there should be clinical trials for the SARS virus vaccine. We still have a lot to learn.
No comments:
Post a Comment