Wednesday, November 3, 2010

Vaccine Awareness Week: If Vaccines Work...

"If vaccines work, then it shouldn't matter if I don't vaccinate my kid."

That argument, or some variation thereon, is fairly common among anti-vaccine folks and the parents who fall for their propaganda. The thinking is something like this: vaccine proponents claim that vaccines work; if they work, they must be 100% effective; if they are 100% effective, then my kid getting sick won't affect anyone that's been immunized; therefore, why should it matter to anyone else what I choose for my child?

There's a couple problems with this line of reasoning.

First is the strawman argument that vaccines are 100% effective. No one, especially not anyone in the pro-vaccine arena, claims that any vaccine is 100% effective. This fallacious argument also tends to be associated with the black-and-white thinking of the Nirvana fallacy, that if vaccines are not 100% effective, then they are completely worthless, so why bother? Vaccines vary in efficacy. Some are over 90% effective. Many are in the 80%-90% range, while some can be extremely low (e.g., the BCG vaccine against tuberculosis, with an overall efficacy of around 50%, a statistic which has not changed much over the years [PDF]).

Because vaccines are not 100% effective, there is always the possibility that an immunized individual is still susceptible to infection. Chris, a regular commenter at Respectful Insolence and other blogs, wrote up a brief comment that nicely illustrates how herd immunity works. I'll copy it here for ease of reference:

Take 1000 people (ignoring the infants under 2 months who cannot be vaccinated, or babies under a year who can only be partially vaccinated), if 5% refuse vaccines then the numbers are:

950 vaccinated persons (assuming full schedule)
50 unvaccinated persons

The pertussis vaccine is actually only 80% effective at worse, so the numbers are:

760 protected persons
190 vaccinated but vulnerable persons
50 unvaccinated persons

There is an outbreak and it gets spread to 20% of the population, then:

760 protected persons without pertussis

38 vaccinated persons get pertussis
152 vaccinated person who may still get pertussis

10 unvaccinated persons get pertussis
40 unvaccinated persons who may still get pertussis.

In Chris' example, we have a total of 48/1,000 who become infected and 192/1,000 who are still vulnerable to infection. What happens if immunization uptake drops further, to say, 15% refusal?

850 vaccinated persons (assuming full schedule)
150 unvaccinated persons

Continuing with the worst-case 80% efficacy of the pertussis vaccine, the numbers are:

680 protected persons
170 vaccinated but vulnerable persons
150 unvaccinated persons

There is an outbreak and it gets spread to 20% of the population, then:

680 protected persons without pertussis
34 vaccinated persons get pertussis
136 vaccinated person who may still get pertussis

30 unvaccinated persons get pertussis
120 unvaccinated persons who may still get pertussis.

This works out to 64/1,000 who become infected and 256/1,000 who are still vulnerable to infection. That means that increasing total refusal by a mere 10% results in a 33% increase in infection rate and susceptibility.

What does this mean for the anti-vaccine argument? It means that if an unvaccinated child gets infected with one of the vaccine-preventable diseases, they can spread the infection to an immunized child for whom the vaccine, for whatever reason, did not work.

All of this ignores, however, the fact that there are individuals who cannot be immunized at all. The decision not to vaccinate has an effect on those individuals, too, so the "if vaccines work" argument doesn't even apply. Here are a couple of the reasons that an individual may not be immunized:

  • They are too young. Newborn infants may not mount an effective immune response to a vaccine to provide lasting immunity if they are too young; the vaccine may have been studied and found not to be safe to give under a certain age; or, the vaccine may not have been studied in children under a certain age and consequently not approved for use in those ages.
  • They may have an existing medical condition for which there is a contraindication. The CDC has a Guide to Vaccine Contraindications and Precautions (PDF) that lists a wide range of medical reasons not to receive certain vaccines.

Choosing to vaccinate decreases your (or your child's) risk of being infected and passing that infection along to people in those two categories above, not to mention the earlier discussion about individuals for whom the vaccine just didn't work. I'll give a couple examples of why the two bullets above are important to me.

Before I get into that, though, it is important to note that many diseases are contagious before any symptoms appear and remain contagious even after symptoms abate. For example, influenza is contagious for about a day before any signs of infection appear, so it is possible to spread an illness even before you know you have one.

Now, onto examples from real life. Several of my friends and coworkers have recently given birth to beautiful little children. Like most people, I take joy in seeing these new additions to the world, and I really do not want to be responsible for any harm to them. By vaccinating, I reduce my risks of being infected and, therefore, passing the infection along to those infants. If I do not get vaccinated, I am at increased risk of infection, and I may, quite unwittingly, infect the newborn child of my close friend, possibly with rather severe consequences. That is a risk that I am not willing to take. I would rather not gamble with the lives and well-being of my friends' newborn sons and daughters.

I also have a friend who is a transplant recipient due to severe diabetes. Before the transplant, he was pretty much on death's door, requiring frequent visits to the ER for dialysis and resuscitation from heart attacks. He got a new liver and pancreas and the difference was like night and day. Instead of lolling to sleep in the corner, he became vibrant and talkative. He no longer needed regular doses of insulin, and visits to the ER gradually became a memory. The only down side is that he needs to take immunosuppressing drugs to keep his body from rejecting the new organs. This means that he is more prone to infection. Again, I really do not want to be responsible for him developing a disease that could very well put him back in the ER or even kill him. By getting vaccinated, I reduce that risk immensely.

There may be other people with whom I come in contact on a daily basis that may be just like my friend, but I might never know. It isn't exactly like they walk around with a big, neon sign above their heads flashing, "I'm particularly prone to infection and serious complications from disease." I may pass them in the supermarket. Perhaps I brush against them on the bus or subway. Maybe they're next to me in the crowd at a concert or play. It certainly would be unreasonable to expect them to stay sequestered away from all other people and not enjoy life. And so I take the responsibility to do what I can do to help protect them.

Finally, in choosing not to vaccinate your child, you are deliberately withholding beneficial medical treatment and increasing the risk of disease, along with the potential complications for someone other than yourself. Every individual certainly has the right to decide, for themselves, what medical interventions to follow. However, when it comes to deciding for your children, you are not deciding for yourself. Further, your children are not your property to do with as you please. You have a responsibility to ensure their welfare and do what you can to protect them from whatever harms can be prevented. Given that the benefits of vaccinating outweigh the risks, it is irresponsible not to vaccinate your child, barring legitimate medical reasons.

The decision to vaccinate or not vaccinate is not one that only affects the person receiving the immunization. It affects every person with whom they come in contact. (The only exception to that is tetanus, which is not contagious. If you want to risk tetanus, knock yourself out.) Whether you like it or not, you, and your child, are part of the herd, part of the community. Your decision has real effects on the spread of infectious diseases. Think of those around you: your friends, your family, coworkers, people you pass in the store. By vaccinating, you reduce your risk of being infected by any of them, and you likewise reduce the chance of spreading infection to them. By choosing not to vaccinate, you are choosing to risk not only your own health or the health of your child, but the health of everyone with whom they come in contact.

If you're interested in more Vaccine Awareness Week posts, there is are lists at Science-Based Medicine and I Speak of Dreams. You can also find more on Twitter by searching for the #vaxfax hash tag.

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