A changing world requires a clear blueprint for disease response
Written by biostatistician M. Elizabeth Halloran, M.D, D.Sc., of the Fred Hutchinson Cancer Research Center and the University of Washington, and University of Florida biostatistician Ira Longini, Ph.D., the article outlines how policymakers and health care workers can use epidemiological methods, statistics, mathematics and models of how well vaccination campaigns work to respond to new, unexpected outbreaks.
“Human connectivity is getting more and more complete. Through jet travel, we can move viruses very quickly,” Longini said. “Viruses can get transported out of previously isolated populations in Africa or other parts of the world within days now instead of years.”
Although the paper was written well before the Ebola outbreak in West Africa, the article addresses that kind of situation. Infectious diseases such as Ebola, for which there is not yet a vaccine or effective treatment, will be a challenge, Longini said.
“We really don’t know how to control these diseases. We don’t have vaccines, antivirals, antibacterials, or whatever is needed to do what we need to do when we don’t know what the next big pandemic threat will be,” Longini said. “This paper gives a blueprint or roadmap of how to work efficiently in that kind of environment.”
The authors suggest creating mobile stockpiles of vaccines for diseases that have them, such as cholera. Statistical models based on other outbreaks — such as the 2010 outbreak of cholera in Haiti — can help inform policymakers and show health care professionals how to administer a vaccine campaign in an efficient and cost-effective way. For example, the researchers found when 60 percent of a population is vaccinated, nearly 100 percent of the population is protected against disease transmission.
The indirect effects of vaccinations are important, said the article’s lead author, Halloran.
“Taking indirect effects into account when looking at the cost/benefit of vaccination makes a big difference for developing countries that are needing to use some pretty expensive vaccines right now,” she said. “If you’re looking at some country that is relatively poor, then taking indirect effects into account could change the equation.”
Halloran said while policymakers want to assess these indirect effects, studies are needed to determine factors in disease outbreak such as the time of infection, the onset and end of a disease’s infectiousness as well as how the disease is transmitted through human contact in social settings such as homes, schools and workplaces.
The models the researchers use can be adjusted to fit differences in population size, structure and the movement of people within a certain population. Still, a changing world presents new challenges in responding to diseases outbreaks.
“It’s like the old Donald Rumsfeld quote: There are the known knowns, there are the known unknowns and the unknown unknowns,” Longini said.
The researchers also are monitoring diseases such as chikungunya and dengue fever. There is currently no vaccine for the viral disease chikungunya, which has flu-like symptoms and a low mortality rate but may cause lifelong arthritis in people who contract it.
“Chikungunya has been around for many years and is causing massive epidemics in the Caribbean right now, spreading to all of Latin America,” Longini said. “It will probably also hit Florida and southern parts of the United States eventually — we know that it’s coming.”
In these cases, the researchers write, policymakers and health care workers can only survey the disease’s progress, work to quarantine it and educate the people living within an outbreak’s zone about how to best avoid transmitting disease until vaccine or drugs are developed.