A virus is not a bacterium, and not quite a cell either: it has no ribosomes of its own, so to multiply it must commandeer the host translation machinery. One full cycle runs from attachment to a receptor through takeover, lysis and spread, and each burst cell releases tens to hundreds of new virions, so the healthy population falls away fast. Antibodies raised by a vaccine coat the spikes and block that very first step, while a variant reshapes those spikes just enough to loosen the old fit.
A virus is not a bacterium, and not quite a cell either: it has no ribosomes of its own, so to multiply it must commandeer the host translation machinery. One full cycle runs from attachment to a receptor through takeover, lysis and spread, and each burst cell releases tens to hundreds of new virions, so the healthy population falls away fast. Antibodies raised by a vaccine coat the spikes and block that very first step, while a variant reshapes those spikes just enough to loosen the old fit.
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