CDC moving quickly on smallpox front

Immunizations, training, vaccine dilution studied

Though officially stating it has no knowledge of any impending use of smallpox as a bioweapon, the Centers for Disease Control and Prevention is scrambling with conspicuous speed to be ready for just such an event. CDC workers from a variety of specialties are not only receiving smallpox vaccinations; they are being trained to give them to others using the old bifurcated needle scarification technique. Even as creation of a new vaccine is fast-tracked, researchers are trying to determine if the current stockpile of 15.4 million doses can be expanded fivefold by simply diluting the vaccine. Based on such actions, it is fair to say the agency is at least highly suspicious that the known stocks of smallpox virus are not safely ensconced in their official repositories in Russia and the United States.

Rapid-response teams to be vaccinated

"CDC is putting together a number of teams, which will probably total over 100 employees, that could be quickly dispatched in a moment’s notice to assist state and local health departments and front-line clinicians investigate suspect cases of smallpox," says CDC spokesman Tom Skinner. "They are Epidemic Intelligence Service officers, laboratorians, and others. Part of this includes vaccinating them against smallpox."

But while confirming that the CDC teams are being trained to administer the vaccine, Skinner would not specify who would be vaccinated following a smallpox bioterror event. "We have a smallpox readiness plan," he says. "Issues around vaccination are covered in that plan. That plan is being finalized. It is considered an operational plan. If we have a case tomorrow, it could be implemented. It covers who should be vaccinated and when."

The general consensus among bioterrorism experts is that those exposed would be vaccinated, because the vaccine can prevent infection and possibly death even if given several days out. Likewise, health care workers and their family members would want vaccine if they are expected to care for the infected. Some aspect of quarantine would no doubt come into play because, unlike anthrax, it will be critical to separate the first smallpox cases and their contacts from the susceptible population.

Using dilution to stretch vaccine stocks

Another aspect of CDC preparations includes the smallpox vaccine dilution study, which is being headed up by Sharon E. Frey, MD, associate professor of infectious diseases and immunology at St. Louis University School of Medicine. The vaccine, known as Dryvax, is no longer produced, but there are 15.4 million doses left. Frey and colleagues are studying the feasibility of dilution procedures that could maintain vaccine efficacy while increasing the available stock by millions of doses. In a study last year, Frey tried a one- to 10-vaccine dilution, which would create a stockpile of more than 150 million doses. However, the resulting vaccine had only a 70% effective rate. "The undiluted vaccine has about a 95% take rate," she says. "It is not perfect, but we would like to be as close to that as we could be."

The new study will include a one-to-five dilution, which should show greater efficacy while increasing the stockpile to more than 75 million doses. "We are looking at a take’ rate for the vaccine, in other words how many people actually develop a typical lesion and whether they have a strong neutralizing antibody response to the vaccine," she says. "We know that the vaccine is still good. We actually titered the vaccine, and it is very similar to its original titer."