I have read that a vaccine against a pathogen typically works by using a dead or weakened version of that pathogen and then inciting an immune response against the pathogen so that the immune system then recognizes that pathogen in the future and attacks it immediately.

However, suppose that a person gets vaccinated against a virus. Why couldn't the virus infect a few cells before it runs into immune system cells and starts replicating as normal? Does the immune system somehow recognize virus-infected cells?

Also, how would a vaccine against a virus that attacks immune system cells work (like HIV, for instance)? In this scenario, wouldn't any immune cell that tries to destroy the virus get infected itself?


Vaccines containing these weakened or killed viruses or bacteria are introduced into your body, usually by injection. Your immune system reacts to the vaccine in a similar way that it would if it were being invaded by the pathogen — by making antibodies. The antibodies react to the vaccine (virus/bacteria) just as they would the live pathogen — like a training exercise against an antigen. Then they stay as amemory in your body, giving you immunity. If you are ever exposed to the real disease, the memory is activated and antibodies are there to protect you.

Moreover if a cell gets infected virally, infected cells produce and release small proteins called interferons, which play a role in immune protection against viruses. Interferons prevent replication of viruses, by directly interfering with their ability to replicate within an infected cell.

  • $\begingroup$ It is better to use the term "pathogens" instead of "germs" especially when the OP is very well aware of the former. Also, it would be great if you could provide some references $\endgroup$ – WYSIWYG Mar 10 at 18:46
  • $\begingroup$ Edited your answer for terminology. If not acceptable, please feel free to roll back. $\endgroup$ – anongoodnurse Mar 11 at 5:49

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