The only problem with such a time period -- proposed by the Centers for Disease Control -- is that the six major interruptions, involving six of eight recommended childhood vaccines, between November 2000 and February 2004 ranged in duration from seven months to 20 months, the scientists report in the April 24 issue of the journal Vaccine.
Spending another $500 million up front would ensure sufficient quantities for a 12-month interruption, said operations researcher Sheldon H. Jacobson, professor of mechanical and industrial engineering at the University of Illinois at Urbana-Champaign.
The CDC's "choice of six months is unclear," given the actual timelines of recent production interruptions, Jacobson said.
"It appears that we are being overly concerned in the short-term over a few hundred million dollars, whereby the potential risk to the 4 million children born every year is so great," Jacobson said. "When you consider how strained the nation's health-care system is right now, a one-time expenditure of a few hundred million dollars of stockpiled vaccines goes such a long way to protecting the approximately 11,000 children born every day in the United States. This is something we can control. It is not clear why it is not being done."
The researchers used a stochastic inventory model in which they considered multiple variables, including differing vaccination coverage rates, getting vaccines on time, production downtime, the ramp-up process to replenish supplies and the number of children born each day. While described briefly in the Vaccine paper, the full technical description of data and the analyses will be published in a separate journal.
"The results suggest that in the event of a vaccine production interruption for any of the vaccines that lasts for eight or more months, there is a reasonably high risk (from 8 percent to 89 percent based on optimistic or pessimistic scenarios) that the proposed vaccine stockpile levels will not be adequate to fully vaccinate all children that require immunization," the researchers wrote.
An interruption of 12 months, they added, would raise the risk of insufficient supplies to between 95 percent and 100 percent. A subsequent problem of shortages is that many children miss their vaccines and must return to their physicians to catch up, but in many cases parents do not follow through with the return visits.
The 15-member Advisory Committee on Immunization Practice establishes the vaccination recommendations for both children and adults. The study considered eight childhood vaccines. The committee added two more vaccines to the 2006 pediatric list.
The proposed stockpile covered in the study calls for vaccines to be stored on a rotating basis, with the numbers of dosages ranging from 2 million for varicella to 10 million for diptheria-tetanus-acellular pertussis.
The recommendations came out of a working group that was formed in 2002 after the U.S. Department of Health and Human Services began an investigation into shortages in pediatric-vaccine supplies. Stockpiles currently exist for five pediatric vaccines: the inactivated poliovirus (IPV); measles, mumps and rubella (MMR); Haemophilus influenzae type B (HiB); Hepatitis B (HBV); Hepatitis A (HAV) and the combination vaccine covering diptheria, HBV and IPV.
Co-authors of the study were Dr. Janet A. Jokela, professor of clinical medicine and associate director of the internal medicine residency program for the UI College of Medicine at Urbana-Champaign; Ruben A. Proano, a doctoral student in the department of mechanical and industrial engineering; and Edward C. Sewell, professor of mathematics and statistics at Southern Illinois University at Edwardsville.
The National Science Foundation funded the project.
Editor's Note: Sheldon Jacobson can be reached by email at shj@uiuc.edu or by phone at 217- 244-7275.
Journal
Vaccine