The optimal balance of vaccine stockpiles

How much is enough? Stockpiling vaccines for eradicated diseases poses particular difficulties // Source: wordpress.com

A model that could be used to guide public health decisions about how much vaccine to stockpile against an eradicated disease, such as smallpox, is published in last Friday’s edition of Vaccine.

Once a disease has been eradicated there is a danger it could reappear, either naturally or as a result of an intentional release by a terrorist group. To address this risk, health authorities may store supplies of vaccine that can be deployed to protect people from infection if the need arises.

Radboud Tebbens and colleagues are the first to use mathematical tools to give the best balance of the various factors that enable optimal emergency stores of a vaccine to be held after a disease has been wiped out.

“Vaccine stockpiling is a complex problem governed by many different factors,” Tebbens, from Delft University of Technology in the Netherlands, told EHTF News. “The model is a framework for how a vaccine stockpile can be optimized.”

Emerging Health Threats reports that authorities face difficult decisions over how many doses of a vaccine should be stored. Too few doses could see many people unprotected and falling ill, but too many doses could lead to a costly excess of vaccine. Getting the correct balance calls for the consideration of many different factors that dictate the production, storage and distribution of a vaccine when an emergency arises, according to the authors.

They devised their model using research studies and reports that detail these factors, which include delays in producing large quantities of reagents used in the vaccines, and the time needed to fill the individual vaccine vials needed for immunization campaigns. The time needed for safety and efficacy testing, and constrains in vaccine distribution and administration are additional considerations.

There are also issues to consider that are specific to eradicated diseases, say Tebbens and colleagues. After a disease has been wiped out, routine immunization may eventually stop. This means any stored doses of the vaccine can no longer be ‘rotated’ with doses in general use, and may expire before they can be administered, they explain.

The end of routine immunization brings a reduction in people’s immunity against the pathogen involved — so once released, it could spread through a population quickly, putting many at risk. It also means that the vaccine will no longer be mass-produced, and this could slow down the rate at which large quantities of the vaccine can be manufactured when needed.

The model takes these issues