I was looking at the CDC Vaccine Schedule for children, and it says that many of the things kids are vaccinated for may show no symptoms.

Do any of those diseases –– mainly haemophilus influenzae, Hepatitis A, Polio and Pneumococcal –– stay in a persons system with no symptoms for a long time?
Does getting a vaccine later in life, but after they've been contracted, without exhibiting symptoms, cure the diseases?
And is it known how kids can be carriers for these diseases (i.e. would every sneeze be riddled with these germs)?

  • 5
    Based on your related IPS.SE question, I suspect what you're really wondering is whether your assumption that "if our children are [or appear] healthy, they can't get anyone sick" is actually correct. You might want to ask about that more directly, to get more applicable answers (for example, if diseases that do have symptoms listed on that chart are contagious for a while before the symptoms show up, that would probably be relevant to the broader question).
    – 1006a
    Commented Jun 6, 2018 at 21:03
  • @1006a You're spot on - but I'd rather have that not be part of this question in the least. I don't particularly want answer jaded by that question, especially on this site. Commented Jun 6, 2018 at 21:07
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    This is an XY problem: You‘re jumping to the conclusion that unvaccinated people can only be a problem if they are contagious without knowledge. However, unvaccinated people enable the survival of diseases for which vaccines are not 100% successful. If an unvaccinated person gets infected and does have symptoms, it would still have spread the disease, ensured its survival and thus created a risk even to vaccinated people. Vaccines are not bomb shells, they are highly efficient, but still, what does a 1% failure chance help you if you‘re the one percent?...
    – Narusan
    Commented Jun 6, 2018 at 21:51
  • 6
    The huge problem I am having with this post is that due to the linking to the other post, a factual right answer (as may be diseases aren’t contagious without symptoms in unvaccinated people), can be misinterpreted and used as a conclusion that unvaccinated people pose no threat. So please ask that question directly, so that I don’t have the feeling this is manipulative.
    – Narusan
    Commented Jun 6, 2018 at 21:53
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    A person going against an extremely robust medical consensus can't plead ignorance.
    – swbarnes2
    Commented Jun 6, 2018 at 22:50

1 Answer 1


Unvaccinated members of a population contribute to the susceptibility of the rest of the population to disease, especially vulnerable people who cannot be vaccinated. This fact is true whether or not infectious individuals are asymptomatic for a long time or a short time.

  1. Many (if not most) infectious diseases are contagious before symptoms clearly manifest - including all 4 of the ones you listed. Infectious diseases rarely fully announce themselves before they are contagious, actually, and often viral shedding is highest at or before onset of symptoms. For example herpes simplex: it actually sheds the most before the stereotypical blister forms. The duration of the asymptomatic period of diseases varies widely - some are carried and spread for years without ever knowing it. Yes, you can catch AND transmit many diseases before you even know you have it.

  2. Each infectious disease has a specific mode of transmission, and survive different lengths of time outside the body - ranging from minutes to years. Some respiratory viruses hang in the air in tiny particles for minutes to potentially hours - and not just by coughing or sneezing, many are transmitted just by breathing out. Without consistent and correct hand hygiene, fecal-oral transmission diseases can spread rapidly whether the person is symptomatic or not. (Especially kids - what kid is 100% perfect with hand hygiene?) Some infectious diseases shed in unpredictable cycles, others shed constantly.

  3. The epidemiology of infectious disease transmission and the impact of vaccination are both crystal clear. Creating herd immunity - minimizing the prevalence of a disease in a population to drastically drop transmission rates (especially for those who cannot be vaccinated for medical reasons) - requires everyone's participation. Vaccination is therefore an issue of both public health and community responsibility.

    • In no uncertain terms: an unvaccinated person poses a health risk to both themselves and to their community.
  4. There is an entire catch-up schedule for a reason - doing it now, even if it's a late start, is far better than never doing it.

  5. If a child already has a disease, unless they are acutely ill, it is generally not harmful to give the vaccine for it. Sometimes it's okay even when they're acutely ill. (But one should always talk with a doctor for advising on one's individual case.) With a few diseases, giving the vaccine can actually help the body prevent the disease from fully developing - if given early enough. But do note this is NOT a reliable treatment, it is a there's-a-chance-it-could-help-so-it's-better-than-nothing type strategy, and only with certain diseases. The ideal situation is to be protected before ever being exposed to a disease.

  6. Again in no uncertain terms: although there are estimates of disease prevalence, including asymptomatic cases, it is impossible to be certain that an asymptomatic unvaccinated child doesn't have an infectious disease - unless you test them for it.

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    @Narusan and OP - I've added a brief statement to the beginning. Feel free to edit if you don't like the wording, but I agree with the sentiment that it is important to emphasize this given the context of the question in a sea of misinformation about vaccines. I think overall the answer does a good job of identifying the other reasons unvaccinated individuals can be an issue in a population, but making this clear in the beginning is important to prevent misinformation from a cursory review.
    – Bryan Krause
    Commented Jun 7, 2018 at 16:55
  • @bryan all that does is unfairly associate me with an anti-vaccine mindset that I frankly don't have. It should be ask about the effects of what are essentially my wife's decisions in consultation with our kids' pediatricians (because she takes them to the doctor, not me) without being labeled a troglodyte. Commented Jun 7, 2018 at 17:18
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    The medical decisions about your children are being made with an anti-vaccine mindset that puts your own and other peoples' children at risk (and adults too). Whether you like it or not, those decisions associate you with that mindset. This answer to your question, however, does nothing to associate you personally to that mindset. This answer only attempts to explain scientific and medical understanding about how infectious diseases are transmitted with or without vaccines.
    – Bryan Krause
    Commented Jun 7, 2018 at 17:23
  • As Sheldon Cooper said, "If influenza was only contagious after symptoms appeared, it would have died out thousands of years ago. Somewhere between tool using and cave painting, homo habilis would have figured out to kill the guy with the runny nose. "
    – mhwombat
    Commented Dec 19, 2018 at 0:59

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