The optimal balance of vaccine stockpiles
into account to arrive at the “optimal balance” between the financial costs of the vaccine, production speed, and the public health costs of leaving people unvaccinated. “It will help discussions on how to manage stockpiles,” says Tebbens.
In the paper, the researchers use their framework to model a vaccine stockpile for poliomyelitis, a viral disease that international health authorities have been pushing to eradicate for many years. Some experts have doubts that polio eradication efforts will be successful, but Tebbens notes that the framework is a template that can be adapted to other diseases.
Smallpox is the only disease to have been eradicated. Emerging Health Threats notes that in an e-mail to EHTF News, Donald Henderson, who led the campaign that wiped out smallpox in the 1960s and 1970s and chaired the WHO advisory committee on setting up a smallpox vaccine stockpile, says the research raises all the right issues that should be taken into account when storing vaccines against an eradicated disease.
He does not believe, however, that an elaborate model can really help to guide smallpox stockpiling decisions. Scientists know the shelf-life of the smallpox vaccine, and how many doses are needed every year to vaccinate laboratory workers and military personnel at risk of the disease, notes Henderson.
They can also estimate the number of doses that need to be manufactured every year to keep the production facilities running and ready for activation during an emergency. “Thus, how much to provide in a stockpile is a fairly simple exercise which, in the end, is the product primarily of informed judgment calls,” says Henderson. A big unknown is the risk of a smallpox release occurring, and “you can’t model that”, he notes.
Henderson says that intelligence information about biological terrorism is limited. “There is no way of determining the size of an attack, where it would happen and how difficult it would be to control,” he explains. These factors play a part in how many vaccine doses will be necessary to control an outbreak.
Some of the challenges of stockpiling may be unique to specific diseases, adds Henderson, because the difference between vaccines can be great. For example, batches of the smallpox vaccine produced in 1958 have proved effective against the disease in 2002, making the expiry date a less important consideration in stockpiles against this disease.
-Read more in Radboud J. Duintjer Tebbens et al., “Optimal vaccine stockpile design for an eradicated disease: Application to polio,” Vaccine 28, no. 26 (11 June 2010): 4312-27 (doi: 10.1016/j.vaccine.2010.04.001) (sub req.)
