I think it is both. The mRNA vaccine immunity did not wane just because of changes in the virus. That was probably a factor but in this case I don't think it was even the biggest one. The immunity just wanes, even to the same strain. It is to do also with the immune system itself.
The antibodies produced by any vaccination series wane, it isn't a surprise that it happened with the COVID vaccines. The mRNA vaccines do induce memory T cells, which is exactly persistent immunity, so the immunity doesn't 'just' wane.
Repeated doses of the vaccine broaden and increase the antibody response, so of course it makes sense to encourage them when infections are raging, and an annual booster will induce an antibody response, providing increased protection for a period of time, so of course it makes sense to encourage them, especially for more vulnerable people.
This inability to look at things in a sort of probabilistic sense, where things can be good without being perfect, is incredibly damaging.
The non-mRNA COVID-19 vaccines that targeted the entire virus rather than just the spike protein generally produced somewhat more durable immunity even after many mutations. In principle it might be possible to make mRNA vaccines that work in a similar way, so I don't think it's a fundamental weakness in the technology.
They did. The AZ vaccine was not mRNA based and was pulled from the market because it killed so many people.
The vaccines had two problems:
1. Spike protein is nasty. It causes clotting and organ damage. Doesn't matter how it gets in your body: virus, mrna, adenovirus, classical grow-it-in-eggs.
2. mRNA drugs specifically rely on special coatings which were as recently as 2017 unable to launch on the market due to toxicity that develops after multiple dosings. There's no evidence this problem was ever solved and Moderna pivoted from drugs to vaccines specifically because they couldn't solve it, the logic being that with vaccines you only have to take them once to get a lifetime of protection so the toxicity doesn't matter (doh).
mRNA is a tricky technology. Several major pharmaceutical companies have tried and abandoned the idea, struggling to get mRNA into cells without triggering nasty side effects
Three former employees and collaborators close to the process said Moderna was always toiling away on new delivery technologies in hopes of hitting on something safer than what it had. (Even Bancel has acknowledged, in an interview with Forbes, that the delivery method used in Moderna’s first vaccines “was not very good.”)
nanoparticles created a daunting challenge: Dose too little, and you don’t get enough enzyme to affect the disease; dose too much, and the drug is too toxic for patients.
Moderna could not make its therapy work, former employees and collaborators said. The safe dose was too weak, and repeat injections of a dose strong enough to be effective had troubling effects on the liver in animal studies.
The drugs it is pushing along now, by contrast, are more modest, relying on single administrations of mRNA.