Vaccine Scares can Perpetrate Below-Optimal Coverage, Spread Infectious Diseases

In places where vaccination is not mandatory, societal pressures can can have a direct effect on the spread of pediatric infectious diseases, according to a new study in the Proceedings of the Royal Society B.

Few debates are more vigorous and vocal than the one surrounding vaccinations. Despite a wealth of scientific evidence that vaccination improves overall public health, a strong anti-vaccine movement exists, fueled by controversies linking vaccinations to autism in children.

By using a series of statistical models, researchers from University of Guelph and the University of Waterloo report that they can foresee observed patterns of population behavior and disease spread at times when anti-vaccine sentiment is running strong, a phenomenon the researchers refer to as a "vaccine scare."

"If vaccination is not mandatory and disease is rare, then a few parents will be tempted to stop vaccinating their children," said University of Waterloo mathematician Chris Bauch, one of the study authors. "More parents adopt this behavior as social norms begin to change and it becomes increasingly acceptable to avoid some vaccines. Obviously, when enough parents are no longer vaccinating, the disease will come back."

Although pediatric vaccination is mandatory across most of North America's public school, the researchers report that the number of parents applying for their children to be exempt from vaccination requirements is on the rise.

Bauch said that as this trend continues, people will come to find themselves in a situation where vaccination coverage has declined and populations are more susceptible to disease.

"Parents are not cold, clinical rationalists who base their decisions only on data. They are strongly influenced by other parents and what they read," Bauch said in a statement. "Our research suggests that health officials needs to have a really good understanding of the social context to better understand vaccine scares and why people refuse vaccines. To do that, we have to develop predictive tools that also reflect social behavior patterns, or we won't be able to accurately represent what is happening during vaccine scares."

Bauch said predictive modeling can be useful for public health officials and vaccine programs alike by showing what may happen in a population where a vaccine scare has taken hold.

"If you've seen a big drop in vaccine coverage and you've seen a surge of disease because of that, you can use these models to predict how long it will take vaccine coverage to recover," Bauch said.

In the future, Bauch said that he wants to use the predictive modeling strategy to create an index of vaccine sentiment across populations, which could be useful in determining which populations are more susceptible to vaccine scares.