Why vaccines *won’t* overwhelm your immune system

A very quick post today, but a topical one given the situation in Wales (and the UK in general) with regards to measles.  The latest press release from the Welsh NHS has said that there are now 765 known cases, and that over 70 of these people have been hospitalised.  That’s one in ten of the people affected who have ended up in hospital.

There has been (entirely reasonable) supposition in the press that the people affected are largely children who were not vaccinated with the MMR due to the completely false suggestion that the vaccine may cause autism or bowel disorders.  It is felt in some circles that the vaccine may somehow overwhelm a child’s immune system, and lead to illness.

Numerous studies have disproven ths link, and the original paper that suggested it has been withdrawn by the publisher.  The paper itself has been called not only wrong, but downright fraudulent.  Sadly this hasn’t been enough to undo the damage done by the original paper, and by the subsequent media storm that erupted around it.  Measles is not a trivial infection, and as the Welsh NHS press release rightly says, “it is just a matter of time before a child is left with serious and permanent complications such as eye disorders, deafness or brain damage, or dies.”

So in light of all that, I stumbled across this quote this morning in an article published at Medscape.  It’s a rather eloquent way of highlighting the scale of immune assault that we all face every single day, and how unlikely it is that any vaccine could pose a risk on these grounds:

In general, however, if you take a step back and look at this question, the notion that the number of immunologic components in vaccines could in some way weaken, overwhelm, or perturb the immune system is fanciful. When we are in the womb, we are in a sterile environment. When we leave the womb and enter the birth canal and the world very quickly, we are colonized with trillions of bacteria, to which we make an immune response. The total number of immunologic components in today’s vaccines is approximately 165. When you think about the number of antigens that you encounter (remembering that a single bacterium has 2000-6000 immunologic components) and that you are making grams of immunoglobulin every day, that the dust you inhale isn’t sterile, and the food and water that you eat and drink aren’t sterile…The notion that vaccines would somehow weaken or overwhelm the immune system is certainly not supported by what we know about immunology and microbiology.

To put it another way, one single bacterium has 12-36 times as many immunologic components as the average vaccine.  The average person has trillions of bacteria on and in their bodies (in fact in terms of cell numbers we’re more bacteria than we are human), so the addition of a few extra antigens in a vaccine is really a vanishingly tiny drop in a huge ocean.

While I’m not trying suggest that vaccines are risk-free (because that can’t be said of any medicine), the risk of being vaccinated is certainly much lower than the risk of complications from catching something like measles.

Postscript: Medscape have a second article about a recent study that found no link between childhood vaccination and autism; it’s worth a look if you have a login.

EDIT: thanks to Nico in the comments for pointing out a factual error.  I originally asserted that by weight a human being is more bacteria than human.  That is of course wrong (we’re 1-3% bacteria by weight).  We do however contain 10 times as many bacterial cells as our own cells.  Which is either quite wonderful or rather creepy, depending on how you look at it.