In order to make the most of the world's limited vaccine supplies—and to halt the spread of a possible influenza epidemic—researchers say that age-related patterns of disease transmission need to be taken into account regarding their distribution.
New findings published in Science suggest that school-age children and their parents should be the highest priority for flu vaccination efforts, rather than younger children and the elderly.
To reach these conclusions, Jan Medlock and Alison Galvani from the Yale University School of Medicine developed a mathematical model of influenza transmission that takes age into consideration, and analyzes the best strategy for distributing vaccines among these different age groups in a way that would minimize the spread of the virus.
"The evaluation of vaccination policies before their implementation is essential to allocate resources and to minimize disease burden," Medlock writes in his report. "Vaccination has the indirect benefit of decreasing transmission, thereby reducing the infection risk even for those who have not been vaccinated... Ethicists have proposed outcome measures that incorporate valuation based on the ages of victims. For example, in terms of years of life lost, children would be valued over adults... However, ethicists and health economists neglect the transmissible nature of influenza in making their recommendations about which age groups should be targeted for interventions."
Medlock and Galvani say that current vaccine recommendations from the U.S. Centers for Disease Control and Prevention (CDC), do not currently take these age-related patterns of transmission into account.
The researchers new model utilizes survey-based data and mortality data from historical influenza pandemics, and considers many factors—death, infection, total years of life lost, and economic costs—in its calculation of the most effective vaccination strategies.
By comparing a theoretical outbreak with past influenza epidemics in 1918 and 1957, the researchers determined that an influenza epidemic in the U.S. could be stopped today with optimal distribution of just about 63 million doses of vaccine—if children (ages 5-19), who are responsible for most transmission, and adults (ages 30-39), who most often contract influenza from their children, are targeted for vaccination first and foremost.
This targeted vaccination would then, in turn, help to protect the remainder of the population from infection, Medlock and Galvani say. Furthermore, the models prediction of 63 million doses is less than the 85 million vaccine doses that are currently administered annually in the U.S. for seasonal influenza.
These results illustrate the importance of considering age-related transmission patterns when allocating vaccines—and the authors suggest that current recommendations of the CDC be revised to minimize the actual impact of a potential epidemic influenza.
"An age-structured mathematical model of influenza transmission has allowed us to determine the optimal allocations of vaccine doses for a variety of measures of population morbidity and mortality," Medlock concludes in his report. "The CDCs age-based recommendations could be significantly improved by reducing the prioritization of the elderly and children under age five, although [their] recent vaccination recommendations for swine-origin H1N1 show marked improvement over the recommendations for seasonal influenza."