Can someone who has been given a vaccine "infect" another person with the virus used in that vaccine? For example, let's say Bill is vaccinated against tuberculosis. If Frank is exposed to Bill, is there a chance he could "catch" the tuberculosis vaccine, and become immune?

  • $\begingroup$ So, A got a vaccine but still got infected by the virus (which is totally possible). And then, you are asking if A can transmit the virus to B? Is that your question? $\endgroup$ – Remi.b Dec 13 '18 at 23:18
  • $\begingroup$ Here are a few things that can help you clarify the question. Who is "they" in the first sentence? Does it refer to "another person" (but then it should be "he/she")? What do you mean by "contacted"? By "become immune", do you mean after the infection happen? If not, why would there be a need for the first person to be infected? Or maybe when you said "infected from viruses", you refered to the neutralized form of the viruses that were injected in the vaccine? $\endgroup$ – Remi.b Dec 13 '18 at 23:24
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    $\begingroup$ I think Jossie is assuming the antigen in vaccines can can be transmitted and infect other people like an ordinary pathogen. $\endgroup$ – Cell Dec 13 '18 at 23:58
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    $\begingroup$ OP, I've edited your question to try to clarify it. Feel free to roll back or further edit if I've misunderstood or missed anything. $\endgroup$ – De Novo Dec 14 '18 at 16:30
  • $\begingroup$ @Jossie, in simple terms: vaccines only contain parts of "dead" pathogens that trigger an immune response to those parts inside the body of the person who was vaccinated. There's nothing to pass on (via a sneeze, cough, etc.). $\endgroup$ – theforestecologist Dec 31 '18 at 3:49

Most immunizations are not transmissible. A few are. To be transmissible, an immunization would have to be a live attenuated vaccine (i.e., a vaccine that can reproduce in the host, but doesn't cause disease), AND have the necessary reproduction rate and virulence factors that would allow for person to person transmission. There are many live attenuated vaccines in use today, but only one that is transmissible, Oral Poliovirus Vaccine, or OPV. OPV is currently not in use in the US, but is used in the developing world, and can circulate in communities. Some would argue that this is a good thing, as it further disseminates immune protection to the population, but it is a little problematic, because it is not without risk, including reversion to a virulent type that can cause Vaccine associated Paralytic Poliomyelitis.

On editing your question, I'm reminded that your example was of TB. I would note that BCG, the vaccination against Tuberculosis, may be a particular case, and I'm not as familiar with it except as a complicating factor in interpreting the results of a TB test in U.S. immigrants. BCG is a live attenuated strain of Mycobacterium bovis, can (rarely) produce disseminated disease itself, and the mycobacterium itself can be isolated in the blood of individuals some time after vaccination. There is also a possible report of vertical transmission of the mycobacterium (from mother to child), but these results use novel methods, and I'm unfamiliar with this group's work. Whether this would lead to immunity of the child is definitely an open question. BCG even when administered in the standard way (as in intradermal inoculation) isn't particularly good at producing immunity, though it is good at preventing meningitis and miliary TB in young children. I'm not aware of any documented case of horizontal person-to-person transmission, but wouldn't declare it impossible.

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