In the event of a large, intentional release of smallpox, the current government policy of post-release surveillance and containment, if quickly implemented, would be sufficient to prevent a widespread epidemic, according to a study by biostatisticians at Emory University's Rollins School of Public Health. Surveillance and containment consist of isolating known cases and vaccinating close contacts.
Delays in isolating cases by even one or two days, however, could hamper control of an epidemic, according to research by Ira M. Longini, Jr., PhD and M. Elizabeth Halloran, MD, Sc, Emory professors of biostatistics and their colleagues Azhar Nizam and Yang Yang, Dr. Longini will present the research at the AAAS Annual Meeting in Seattle on February 14.
Although mass vaccination during or before a smallpox attack would result in fewer cases and deaths than would surveillance and containment, the researchers concluded that an increased rate of vaccine-related serious illness and death would offset the slightly lower number of smallpox illnesses and deaths, especially since no one knows when or where an intentional release of smallpox would take place. The scientists also concluded that even if a particular smallpox virus were altered to cause more serious, or hemorrhagic cases than the ordinary virus, surveillance and containment would still be effective, although more deaths would occur.
In an earlier study (Science, Nov. 15 2002), the researchers concluded that targeted vaccination of the close contacts of infected individuals during a smallpox outbreak following a small attack could rival the effectiveness of mass vaccination, given a sufficiently high level of immunity within the population. However, as of May, 2003, fewer than 35,000 people had been newly vaccinated against smallpox, and many states had temporarily halted their smallpox vaccination programs. Although routine smallpox vaccinations were stopped in 1972, recent studies have shown that previously vaccinated individuals retain substantial immunity.