Finally boostered

Hooray, I am finally boostered! I did not mind what I would get, but ended up for the 3rd time getting the BioNTech/Pfizer mRNA vaccine.

UPDATE (23.01.2022):
I received some feedback concerning this 2-sentence blog post. I never really think much about the vaccination anymore. To me, the situation appears very clear from a science-based medical perspective. Below, I will keep adding answers to some questions and statements.

1. I do not believe the >90% efficacy of the mRNA vaccine.
   The >90% efficacy of the BioNTech/Pfizer mRNA vaccine in the phase III trials does not mean that equally high numbers are achieved after FDA approval in real life. There are many reasons why the real effect is likely lower, but perhaps the biggest factor is that the subjects that participated in the phase III clinical studies are NOT representative of the whole population. In fact, the homogeneity of the subjects is a desired property of a phase III study, because it makes the interpretation of the results so much easier. But that is not a good argument against vaccination. No vaccination is 100% effective and if reasonably deployed, even vaccinations with efficacies as low as 50% can make a big difference. However, it is important that the vaccinee is aware of the imperfect protection and behaves accordingly. Otherwise, the feeling of being protected can result in more risky behavior and therefore paradoxically in more infections.
2. Why would the current mRNA vaccine protect from Omicron? The mRNA vaccine was designed based on the original Wuhan-Hu-1 strain and Omicron is totally different!
   It is correct that Omicron has 33 amino acid changes in the spike protein compared to the wildtype Wuhan-Hu-1. The Delta variant has only 8 amino acid changes. Given that the whole spike protein is 1273 amino acids long (Wuhan-Hu-1), these proteins are still highly identical and will have largely the same structure, but not a completely identical structure*. Therefore antibodies generated against the mRNA vaccine will still recognize the spike protein of Omicron, but less efficiently than they would recognize the spike protein of the original Wuhan-Hu-1 strain (they have a lower affinity). However, one can - up to a certain point - compensate for lower affinity by increasing the amount (concentration) of the antibody and that's exactly what the 3rd shot is accomplishing.

   But there's another angle to this: The fact that pushing the antibody response might lead to a spillover from the IgG-dominated response to the production of some IgA antibodies. Whether all of these antibodies are de-novo responses or whether some result from switching of antigen-experienced cells (from IgG to IgA) is unclear. Theoretically, such a switch would be possible to both IgGa1 and IgGa2 because the necessary DNA sequences are still available downstream aven after the initial class switch. From IgG1 and IgG3 the switch would be possible to both IgA1 and IgA2; from IgG2 and IgG4 the switch would only be possible to IgA2.

   In any case, even though not dominant, there are also IgM plasma cells and IgM memory cells, which could theoretically undergo a class switch. The same is true for hypermutation. Although these cells can hypermutate they mostly do not hypermutate (or at least not much). Instead, they maintain a lower affinity and therefore a broader reactivity, resulting in a specific capacity to cope with variant forms of pathogens, which might induce them again to undergo further maturation in germinal centers.

   I have no clue which of these scenarios is playing out in SARS-CoV2 infected humans who have been primed three times by the mRNA vaccine. I assume that nobody really knows, but exactly the fuzziness of the immune response is what makes it resilient towards any type of challenge. I trust my immune system to be fuzzy and smart enough to react to the 3rd shot with a variety of heuristic strategies that have been proven in the evolutionary past to mostly work.

* In addition, Delta has one 2-aa deletion compared to Wuhan-Hu-1, and Omicron has one 2-aa-deletion, one 3-aa-deletion and one 2-aa-insertion.