Response planning for potential influenza pandemics may significantly underestimate the consequences of such pandemics, researchers suggest.
A major collaboration between four US research centers—the Argonne, Los Alamos, and Sandia National Laboratories, and the National Renewable Energy Laboratory—has highlighted three factors that could ultimately determine whether an outbreak of influenza becomes a serious epidemic that threatens national health.
Jeanne M. Fair, PhD, and colleagues used sensitivity analysis to uncover what they believe to be the most important disease characteristics pertaining to the spread of influenza infection: the fraction of the transmission that occurs prior to symptoms, the reproductive number, and the length of each disease stage. Their use of data from past pandemics, as well as information on potential viral evolution, demonstrates that current response planning may underestimate the pandemic consequences by a factor of two or more, they contended.
“It has become critical to assess the potential range of consequences of a pandemic influenza outbreak given the uncertainty about its disease characteristics while investigating risks and mitigation strategies of vaccines, antiviral drugs, and social distancing measures,” the researchers explained. Their simulation model incorporated uncertainty in the evolution and characteristics of the pathogen and differences in the epidemic response, and uncertainties in the sociological response to a pandemic.
The team said that they have been able to develop a worst-case scenario for all possibilities considering mortality rates and infectiousness of a hypothetical H5N1 avian influenza epidemic based on current knowledge and historical patterns dating back to the 1917-1918 global pandemic, and suggested that it could be up to four times as lethal as that pandemic. Moreover, their simulation suggested that the use of antiviral drugs may not be as effective as healthcare authorities would hope. On a positive note, they have found that social distancing could be the most effective way to contain the spread of infection, usefully reducing symptoms by an average of 16%, although it will cost 50% more than antiviral use through lost working days and commerce.
“Do we prepare for the worst-case scenario when preparing for a pandemic?” Fair asked. “While the worst-case scenario is indeed the worst, it may not be as likely. As far as mortality rates, the 1918 [pandemic] was the worst but really still was only around 2%, which could be considered low.”
The current study supports earlier findings that no single strategy is best and that a mix of pharmaceutical and nonpharmaceutical interventions will be needed to contain the disease and reduce the total number of deaths, the team said. It would be prudent to incorporate these findings in planning for the next pandemic, they added.
Fair, JM, Powell DR, Leclaira RJ, et al. Measuring the uncertainties of pandemic influenza. Int J Risk Assess Manage. 2012;16(1/2/3):1-27.