Refusing to Vaccinate Leads to Outbreaks

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August is National Immunization Awareness Month. I get it. The decision to vaccinate yourself or your child is a contentious subject. Stacy Morrison's post at the beginning of the month (or more specifically the comments it generated) proved that point. This conversation is important and the facts are important - even if it isn't (in some circles) popular. The comments section got very heated, and I think Stacy did a fantastic job of staying above the fray without backing down on her stance.

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Image: Romana Klee via Flickr

A paper was published in February in PLOS ONE (not behind a pay wall, so I encourage you to read it if you're interested) titled "Positive Network Assortativity of Influenza Vaccination at a High School: Implications for Outbreak Risk and Herd Immunity." It's a bit of a mouthful, I'll admit. The authors also tend to speak about the outcomes in statistical terms, so it's not likely to show up on a NY Times bestseller list any time soon. For everyone's convenience I am going to summarize the main points that they made in plain English.

Work done by previous research teams has already shown something incredibly interesting (in my opinion). In the new study, the authors showed that when they evaluated the distribution of vaccinated and unvaccinated individuals in a high school, the groups tended to cluster. Now in this case, they were looking at the seasonal flu shot, and not the standard childhood vaccinations, but the principles can be extended (and have been in other instances) to all vaccinations.

What the authors found was that students tended to positively associate (as in, were more likely to) with students of a similar vaccination status -- more so than if they were to randomly associate. When the researchers ran outbreak simulations from the groups that they established from the surveys collected, they found that the clusters led to larger potential outbreaks than a random clustering would have -- 22% larger outbreaks in fact.

What this means is that clusters of unvaccinated individuals, who due to social stratification because of similar opinions, reduce the herd immunity of the community and lead to more frequent and/or larger outbreaks of said disease.

Now before you write this off as "oh it's just the seasonal flu," the exact same issue has cropped up time and again with more serious diseases. The Whooping Cough is a well known example, but it's pretty controversial so let's talk about something that I think everyone can agree on.

Measles.

Measles is insanely contagious. It spreads through microdroplets in the air (airborne transmission), and a person is contagious up to five days prior to the onset of the rash symptoms. On average it takes about 2 weeks from the time a person is exposed until they begin to develop symptoms -- which means that this disease can spread extremely quickly and relatively silently at first -- if there are enough people around who are at risk for contracting it.

There have been outbreaks here in the US (despite being declared "eradicated" in 2000), as well as England, Switzerland, the Netherlands, and many other locations with high vaccination rates. It really puzzled the hell out of physicians and researchers, until they took a closer look at the distribution of vaccinations.

In the Netherlands, for example, it was noted that the outbreaks occurred mainly in populations that consisted of a religious group that did not vaccinate. In other countries it was shown that disease outbreaks also clustered with regions that were anti-vaccination for one reason or another, despite the overall high coverage nation-wide. Measles, by the way, requires a 90%+ vaccine coverage to be contained due to its highly infectious nature. Studies showed that the heterogeniety in vaccinations due to opinion makes a 90% coverage function more like a coverage of less than 70%.

Researchers have since realized (as I think all of us have at this point) that vaccination coverage in countries like the US which have excellent access to vaccines, is heterogeneous due to opinions on vaccination. And that this heterogeneity is linked to the outbreaks we have been seeing lately in these diseases.

In the end what this means is that people who are unvaccinated are putting themselves at more risk than they realize. So many people (myself included) have made the argument that it is socially irresponsible not to vaccinate due to loss of herd immunity, but it appears that even more than that, you're putting yourself at much greater risk by choosing not to vaccinate than you thought.

The chances are that if you choose not to vaccinate, you probably hang out with other people who also choose not to vaccinate. The key to stopping disease transmission is to interrupt the spread (through vaccinated individuals), which protects unvaccinated individuals as well. But in these substantial (and growing) social communities of people who are voluntarily abstaining from immunization, those blocks to transmission are lost, and the likelihood of disease specifically affecting your community is much higher.

I'm not making the social responsibility argument anymore.  I'm asking you for the sake of you and your family to consider the enormous risks you're placing yourself in.

Many times recently I have heard the mantra "I've heard of plenty of people who regret vaccinating, but I've never heard of anyone who regrets not vaccinating" and to those people I want to leave these final thoughts, better expressed by the parents who experienced them than myself:

Okay, so not quite final thoughts.  I have one more thing on the topic of health and vaccination:

For every person out there who thinks that unvaccinated children are healthier than vaccinate children and are quick to point to Google results that back them up, I want to make something extremely clear. Practically every single page that refers to a "published study" is referring to a survey conducted on the Internet that was publicized through social media. (I haven't read every single page so if you see one linking to a different published study, please drop me a link.)

While the numbers involved are large (13000+), the survey was shared through social networking and word of mouth. Just like the studies I discussed earlier showed a clustering of people based on opinions on vaccination, this study is also subject to the same sort of bias in assortment. What I mean to say is that the people who filled out the survey were more likely to have either a) a positive opinion on not vaccinating or b) a negative experience after vaccination. People who have had a neutral (or positive) experience with vaccinations are far less likely to have taken the survey, or even be aware of its existence for that matter. It's very similar to the phenomenon in online reviews of restaurants or stores that people are much more likely to leave a negative comment than a positive.

The survey results page is also extremely misleading in that it references an actual scientific study conducted in Germany that compared the health of vaccinated and unvaccinated children. In this study the families were randomly selected from 167 locations scattered across all parts of the country, and parents were asked if their children had ever been diagnosed with measles, mumps, rubella, and pertussis, along with atopic diseases like cold/flu-like infection, tonsillitis, herpesvirus infection, bronchitis (not when asthma was present), gastrointestinal infection, allergic rhinoconjunctivitis, atopic eczema, bronchial asthma, etc. It's also worth noting that 13000+ children were included in this study as well.

The results were exactly what you would expect: unvaccinated children had a 10-17% lifetime risk of developing one of the big vaccine-preventable diseases (depending on the disease) while vaccinated children had only a 2-7% chance (again depending on the disease).

Even more interesting though was the data showing that for all other common illnesses (including allergies, colds, infections, asthma, etc) the two groups were not statistically significantly different. This is science lingo that means that the differences between the groups cannot be explained by the grouping itself, and are due to random chance. Essentially what they are saying is that there is no evidence of association between general heath of children and their vaccination status (excluding the vaccine-preventables.

Let me repeat: there is no scientific evidence to support the assertion that unvaccinated children are healthier than vaccinated children.

If you are one of the fortunate families that has been extremely healthy and never had a brush with a serious disease, you're lucky. Literally. That is all that it is. Notice that even the vaccinated kids in the German study only experienced any illness (at maximum) 30% of the time. However, should something like measles come calling you need to understand that 90% of the people who are exposed (and susceptible) to it get sick, and 10% of those infected will die.

In conclusion, I'm pleading with those of you who don't vaccinate to re-think your decision. If not for the immuno-compromised (like my father who has ALS and is at constant risk for contracting, and dying from, airborne diseases), the pregnant, the very old, or our smallest youngest babies who can't get their shots yet, then do it for yourself, your kids, and your friends. Because the numbers show that its going to be you who are the worst affected when disease strikes.

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