From herd immunity and complacency to group panic: How vaccine scares unfold

[Dead_Parrot]

The mathematics of woo.

Worries over vaccine risks can allow preventable contagious diseases, such as measles and whooping cough, to make a comeback. A new study, published in PLoS Computational Biology, shows how to predict ways in which population vaccinating behavior might unfold during a vaccine scare.

"These findings might help in evaluating and developing global immunization programs and public health policy", said Professor Chris Bauch of the University of Guelph's Department of Mathematics and Statistics.

Prof. Bauch and Samit Bhattacharyya of the University of Utah developed a mathematical, "Behavior-incidence" model based on game theory and social learning. They tested the model with real data from two infamous vaccine scares in England and Wales: the 1970s pertussis outbreak and the measles-mumps-rubella vaccine scare in the 1990s. In both cases, the publication of alleged vaccine risks was followed by a media firestorm in national newspapers, television, and radio. In light of this, the fact that it took 4-5 years for vaccine uptake to bottom out was puzzling. They found that the model could explain the patterns of the vaccine scares very well, and could also be applied predictively to the data sets.

The model captured the interplay between disease dynamics and vaccination behaviour during those episodes. One of the theoretical dynamics for the model was the phenomenon known as "herd immunity"; an entire population—including unvaccinated individuals—can be protected from infection by vaccinating only a certain percentage of the population. This suggests that immunization programs can be victims of their own success as past vaccinations drive disease incidence to such low levels that unvaccinated individuals feel no incentive to get vaccinated, creating ideal conditions for vaccine scares and thus future outbreaks.

More: http://www.eurekalert.org/pub_releases/2012-04/plos-fhi040212.php
Paper: http://www.ploscompbiol.org/article/info%3Adoi%2F10.1371%2Fjournal.pcbi.1002452

[trotsky]

1. "This suggests that immunization programs can be victims of their own success"`

Suggests? I assert the absolute truth of that statement.

The near-elimination of most common childhood diseases (and the eradication of smallpox) has meant generations of people could grow up without even seeing someone who was blinded or suffered extreme brain damage from measles. Someone in an iron lung because of polio.

Because they lack these reference points, they cannot perform an accurate risk assessment when it comes to vaccines. A literal one-in-a-million chance of a serious vaccine reaction becomes worse than anything those diseases can do - because from their experience, those diseases do NOTHING.

The most you'll get out of those kinds of people is an off-the-cuff dismissal that anything those diseases might cause could be easily treated with some Tylenol and quarantine. Of course, I've also met a few - including right here on DU - who think that the population needs a little weeding out of the weak and susceptible anyway.

[MineralMan]

2. Excellent points!

It's been a long time since mothers sat with a child with diphtheria. A very long time. The same can be said for a number of very dangerous childhood diseases. These days, most doctors haven't seen a case of many of the childhood diseases that were once common. That encourages complacence that is very worrisome.

[SheilaT]

3. I just want to reinforce what

trotsky and Mineral Man have said.

I'm old enough (63) to have gotten all the old childhood disease. My two sons got chicken pox, and first son got Fifth Disease.

My mother was born in 1916 and I once asked her if she'd ever seen smallpox (she became a nurse in the 1930s) and she said no, but there was a family on her street when she was young that had several members come down with smallpox because they hadn't been vaccinated.

My sister's oldest (now 28) had several bouts of scarlet fever as a child, but for reasons I don't fully understand, scarlet fever became vastly less virulent during the 20th century, and now is no big deal as long as it's treated -- with antiobiotics, I think, but I'm not sure.

What we're all used to anymore is that people die from accidents or various cancers or heart disease, not the viral and bacterial illnesses that used to carry us off. I have seen charts showing the changes in the leading causes of death, and even if you don't know much else, you can see the impact of vaccines, better nutrition, and (this is the real biggie) vastly improved sanitation.

With regards to that last, every time I hear or read people freaking out about the possibility of another flu pandemic as in 1918, I point out that there are substantial differences in many things since then, not the least of which is indoor plumbing and a vast increase in hand washing.

I once read that in the 19th century many more people died from stomach cancer than do today because of changes in food preservation. Apparently older methods tended to induce stomach cancer.