Is it known how often unvaccinated children are contagious with symptom free diseases?

Question

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)?

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.