It is possible that some spike proteins escape. For example, as soon as killer cells detect that a cell presents alien stuff, it kills the cell before more stuff gets produced. While the killer cell tries to eat the cell, there can some stuff escape anyway. Scaling isn't possible as long as the mRNA doesn't get replicated. Viruses replicate RNA, but a normal cell doesn't replicate mRNA it because mRNA is created in the nucleus on demand as DNA copy - if the cell needs more, it creates more DNA copies. However, when a virus replicates and many cells all over the body start producing spike proteins - that is another animal. But there are people who survive this process without symptoms (even when having antibodies later). So it seems that the spike proteins are not extremely dangerous. edit: > And isn't it true that not all Spike proteins are the same and the 's protein here may be more destructive? They used the sequence from the original Wuhan virus for the vaccines. There are some variants out in the wild now, but they don't seem to be much different. Most likely, the spike protein was so highly optimized for humans (the result of the gain-of-function research), that most changes will render it useless. This is why we haven't seen the millions of re-infections expected for a seasonal virus.