system
Given the following post, respond as if you're commenting on Reddit:
human
Why are some vaccinations live virus while some are not?

Why are some vaccinations "required" to use the live attenuated virus rather than dead?  Is there a biological reason why only some viruses are still effective dead, or do they both work but there is a preference for live virus in some cases?  

I know that, for example, immunocompromised patients can not get a live-virus vaccine, which could leave them open  to illness.  Wouldn't it be better overall to use "dead" virus vaccinations in all cases to get more herd immunity coverage?
gpt
For safety reasons, we’d rather use a “dead” virus or just a part of the virus (one or two proteins). However, not all of these are immunogenic (i.e. produce a strong immune response). In those cases, we have to use a live attenuated virus (i.e. a virus that has been weakened). These aren’t good for immunocompromised, like you said, because they do have a chance of reversion to virulence (“full strength”). But live viruses make better vaccines because they act the same way the real virus would act, meaning that they elicit the same or similar immune response. It’s basically a toss up between safety and efficacy.