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Biosecurity BriefingNew Study Suggests Healthy Young Adults Should Receive Greatest Priority for Vaccine in Flu Pandemic By Jennifer Nuzzo, July 18, 2008 A new study published on August 1, 2008, in the Journal of Infectious Diseases (JID) argues that limited quantities of pandemic influenza vaccine should be reserved for those who are expected to experience the greatest years of life lost (YLL): healthy young adults. This conclusion differs from the vaccine allocation scheme in the current draft of the U.S. plan for vaccine prioritization, which ranks young, healthy adults among the lowest priority for vaccination.1 There has been much debate about how best to allocate scare quantities of vaccine during an influenza pandemic. Under the current draft U.S pandemic preparedness plan, seniors (≥65 years of age) are prioritized over younger healthy adults in the general population (ie, not those adults who are considered key government and healthcare workers or emergency responders) in all pandemic scenarios. The authors of the JID article note that the prioritization of seniors in the scheme is derived from “conventional vaccination strategies [that] focus on those at highest risk for severe outcomes.”1 However, the authors argue that these qualitative conventional vaccination strategies fail to consider the consider that:
To address some of issues, researchers from the National Institutes of Health, New York City’s Department of Health and Mental Hygiene, and George Washington University conducted a quantitative analysis of the effects of pandemic flu that specifically considered the differential population-level effects of using vaccine to prevent death in younger and older persons under three pandemic scenarios (a severe 1918-like pandemic and milder 1957- and 1968-like pandemics). For each of the three scenarios, the authors calculated the potential number of years of life lost (YLL) for various age groups, using age-specific mortality rates documented in the scientific literature and from historical records from New York City. The YLL measure “integrates mortality risks in various age groups with age differences in life expectancy” and is a tool that is “commonly used as a metric in public health decision making, particularly for vaccination recommendations.”1 The authors found that when “YLL are considered rather than simply deaths, the impact of pandemics is more pronounced in younger populations.”1 When they took into account differential vaccine efficacy with age, they found “an even greater shift in vaccine benefits toward younger age groups,” particularly in the 1918-like scenario in which the difference in mortality rates between younger and older persons was most pronounced.1 For such a scenario, the authors suggest that persons <45 years old represent an optimal group, as prevention of YLL per dose of vaccine is greatest in this group. The authors also suggest that the benefits of vaccinating younger persons may be greater than their analysis suggests, as their analysis only considered the direct effects of pandemic vaccine among vaccinated individuals. Other studies have predicted that vaccinating children may reduce the spread of illness within the rest of the unvaccinated population, as children are thought to play a key role in community-wide disease transmission.1 Although the authors stress that this analysis does not represent “an endorsement of any particular policy” their findings highlight “how the choice of health outcome metrics such as YLL can influence the prioritization of age groups to vaccinate in pandemic settings” and “shows that the vaccine priority scheme for seasonal influenza is not optimized to mitigate the impact of pandemic influenza.”1 References
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