Voluntary vaccination programs shown effective for some diseases

"Conventional wisdom – and conventional theory – tells us that when infection can potentially be spread to almost everyone in a community, such as for measles, a disease outbreak can never be contained using voluntary vaccination," says Chris Bauch and Ana Persic, researchers from the University of Guelph. "However, our work shows conventional wisdom may be wrong for diseases that are spread primarily through close contact, such as smallpox." Their findings appear in the open-access journal PLoS Computational Biology on February 6th.

Previous studies have suggested that voluntary programs cannot be 100% effective due to the self-interested behavior of individuals. However, most mathematical models used in these studies assume that populations mix homogenously – in effect, that an individual is just as likely to be infected by a complete stranger as by a close friend or family member. But that is not how infections spread with diseases like smallpox or SARS, which are predominantly to close social contacts.

In this new study, Bauch and Perisic analyze "free-rider" effects under voluntary vaccination for vaccine-preventable diseases where disease transmission occurs in a social network. Individuals choose whether to vaccinate based on the risk of infection from their neighbors and any risks associated with the vaccine itself. Neighbors of an infected person will vaccinate as soon as their neighbor's symptoms appear, so when neighborhood size is small, voluntary vaccination results in rapid containment of an outbreak. As neighborhood size increases, a threshold is reached beyond which the infection can break through due to the decisions of neighbours who choose not to vaccinate.

"This approach injects greater realism into the transmission modeling of close contact infections and gives us a much more nuanced picture of how people's behavior influences the effectiveness of voluntary versus mandatory vaccination policies," said Bauch. "For those pathogens that are difficult to transmit, the conventional wisdom that free-rider effects will make eradication difficult under voluntary vaccination may be wrong."

PLEASE ADD THIS LINK TO THE PUBLISHED ARTICLE IN ONLINE VERSIONS OF YOUR REPORT: http://dx.plos.org/10.1371/journal.pcbi.1000280 (link will go live upon embargo lift)

CITATION: Perisic A, Bauch CT (2009) Social Contact Networks and Disease Eradicability under Voluntary Vaccination. PLoS Comput Biol 5(2): e1000280. doi:10.1371/journal.pcbi.1000280

CONTACT:

Chris Bauch
519-824-4120 ext. 53079
cbauch@uoguelph.ca

Barry Gunn
519-824-4120 ext. 56982
bagunn@uoguelph.ca

Lori Bona Hunt
519-824-4120 ext. 53338
lhunt@uoguelph.ca

This press release refers to an upcoming article in PLoS Computational Biology. The release is provided by the article authors and their institutions. Any opinions expressed in this release or article are the personal views of the journal staff and/or article contributors, and do not necessarily represent the views or policies of PLoS. PLoS expressly disclaims any and all warranties and liability in connection with the information found in the releases and articles and your use of such information.

PLoS Computational Biology (www.ploscompbiol.org) features works of exceptional significance that further our understanding of living systems at all scales through the application of computational methods. All works published in PLoS Computational Biology are open access. Everything is immediately available subject only to the condition that the original authorship and source are properly attributed. Copyright is retained by the authors. The Public Library of Science uses the Creative Commons Attribution License.

The Public Library of Science (PLoS) is a non-profit organization of scientists and physicians committed to making the world's scientific and medical literature a freely available public resource. For more information, visit http://www.plos.org.