In a typical year, 10-20% of the US population is infected with the influenza virus [1
]. Worldwide, influenza results in 250,000 to 500,000 deaths annually [2
]. The primary method for influenza prevention is vaccination, which is usually 60% to 90% effective depending on the individual [2
]. However, these vaccines are created based on predictions about what strains of influenza will be most prevalent in a given influenza season. Sometimes, as in the current H1N1 “swine-origin influenza”, a strain of influenza undergoes a sudden genetic shift, meaning that there is no vaccine readily available [3
]. In other cases, such as the 2004-2005 factory contamination, the supply of vaccines may be less than expected [4
]. In such situations, mass vaccination against influenza (as is attempted yearly) is not possible, and governments need to issue recommendations about how to most effectively use the limited number of vaccines in order to prevent or control a possible pandemic.
This presents an interesting policy dilemma: to whom do we distribute these vaccines? Current CDC recommendations prioritize, in the event of a pandemic: “critical occupations,” including deployed forces, healthcare workers, and emergency responders, and the “high risk population,” consisting of pregnant women, infants, and toddlers [5
]. This first tier for vaccination comprises 24 million people. The reasoning for prioritizing these groups is that the critical infrastructure workers are vital to keep the nation running, and vaccinating pregnant women, infants, and toddlers will protect the highest-risk groups of the population [5
There is a significant body of publications regarding influenza vaccine distribution [5
]. Prioritization for vaccination, of course, depends partly upon the goal to be accomplished with the vaccine: various goals include protecting those most at risk, minimizing the number of infections, reducing influenza-related mortality, ensuring public order, saving the greatest number of life years, and reducing the economic costs of an influenza outbreak. In a pandemic, one vital priority is to slow transmission of the disease in order to prevent it from spreading out of control [9
Those most important in sustaining transmission of influenza in the community are schoolchildren, and their vaccination may have a significant indirect effect on the rest of the community through increased herd immunity [7
]. Therefore, it is reasonable to consider other vaccination strategies, including placing a higher priority on vaccinating schoolchildren.
The focus of this research is to determine the effects of age-targeted vaccination on the transmission of influenza, not only among the general population but also among varying age groups, and household sizes. The goal is to study the results of applying the same vaccination strategies in two different metropolitan areas, Miami and Seattle, where the population differs significantly in age and household size distributions.