A reader asks:

My child is vaccinated but spends time with a few children who do not have all of their vaccinations. Is my son more susceptible to dangerous diseases?


This is an excellent question.  I’ve made this point many times before:  Immunizations protect your son, as well as those around him.  That “herd immunity” is why leaving some in the community unvaccinated is dangerous for everyone, especially the unvaccinated, and those around him.  Your son is less susceptible to these dangerous diseases if he is completely vaccinated.  But, he is not perfectly non-susceptible, either.

Immunizing your child completely — and on time — may protect him completely (he won’t get sick) if he is exposed to measles, or pertussis, or pneumococcal-caused meningitis (or any of the other diseases we immunize against).  Or, it may partially protect him, whereby he contracts the disease but does not get severely ill.  The problem is, even if he has been completely immunized on time, if he gets even mildly sick from the infection, he is contagious and can transmit the infection to others who are at greater risk of infection.

People at greater risk of infection are, in no particular order:

  • Infants born prematurely.
  • Infants who are too young to receive a protective number of vaccines.
  • Children who are un-vaccinated, under-vaccinated, or not vaccinated on time.
  • Children who are not vaccinated because vaccinating them is contraindicated (due to illness, ongoing treatments, or prior, extremely rare, reactions to the vaccine itself).
  • Children who are immune-suppressed (their immune system is not working well).  Children on chronic steroid therapy to treat their connective tissue disorder or kidney disease, or children receiving chemotherapy for their cancer — many of these children are well enough to attend school despite their diagnoses and therapies, and they rely on other children to be completely immunized.
  • Adults who are immunosuppressed due to diseases (like cancer) or treatments (after an organ transplant).  There are a lot more adults — parents, grandparents, friends, coworkers, neighbors, casual acquaintances (say, at church or a restaurant) — than children in this category.
  • Older adults whose vaccination protection has waned over the years.
  • Any adult who is fighting another illness may be susceptible to contracting a new one.  This is especially true in the elderly, or in any person who suffers from a chronic medical condition.


Immunizing your child completely, and on time, is the most important thing you can do to prevent these vaccine-preventable illnesses.  Keeping him well-nourished, not obese, and away from tobacco smoke and other pollutants (which are harmful to protective respiratory defenses) can also improve his odds of avoiding these diseases.

Parents who choose not to immunize their children (or themselves) put everyone at risk, and benefit, exactly… no one.

I don’t dismiss parents who worry about what they read and hear about vaccine safety.  After all, parents don’t want to do anything that could potentially put their children in danger.  Smart parents know that nothing in life is 100% safe, vaccines included.  But vaccines are pretty darn close (and much, much, much safer than the risks associated with not being vaccinated, or riding in a car, or eating at a restaurant, or, even, breathing the air in some places).  Vaccines — the miracle of modern medicine — are not all that complicated.  It’s pretty cool, and not too hard to understand, how they work.

Looking at vaccines on an individual level isn’t enough.  It’s a small world.  We’re all in this together.  Immunizing one helps immunize us all.  In this second decade of the twenty-first century, we should be looking at vaccines with hope, and not with fear.

More PediaBlog on vaccines here.