Determinants of Influenza Mortality Trends: Age-Period-Cohort Analysis of Influenza Mortality in the United States, 1959–2016

Abstract

This study examines the roles of age, period, and cohort in influenza mortality trends over the years 1959–2016 in the United States. First, we use Lexis surfaces based on Serfling models to highlight influenza mortality patterns as well as to identify lingering effects of early-life exposure to specific influenza virus subtypes (e.g., H1N1, H3N2). Second, we use age-period-cohort (APC) methods to explore APC linear trends and identify changes in the slope of these trends (contrasts). Our analyses reveal a series of breakpoints where the magnitude and direction of birth cohort trends significantly change, mostly corresponding to years in which important antigenic drifts or shifts took place (i.e., 1947, 1957, 1968, and 1978). Whereas child, youth, and adult influenza mortality appear to be influenced by a combination of cohort- and period-specific factors, reflecting the interaction between the antigenic experience of the population and the evolution of the influenza virus itself, mortality patterns of the elderly appear to be molded by broader cohort factors. The latter would reflect the processes of physiological capital improvement in successive birth cohorts through secular changes in early-life conditions. Antigenic imprinting, cohort morbidity phenotype, and other mechanisms that can generate the observed cohort effects, including the baby boom, are discussed.Electronic supplementary materialThe online version of this article (10.1007/s13524-019-00809-y) contains supplementary material, which is available to authorized users.

Tissue-resident CD8+T cells drive age-associated chronic lung sequelae following viral pneumonia

“…Aging is associated with enhanced development of a number of chronic lung diseases including chronic obstructive pulmonary diseases (COPD) and pulmonary fibrosis [65]. Interestingly, aging is also associated with increased susceptibility of acute lung injury and severe disease development following respiratory viral infections such as influenza virus and SARS-CoV-2 [17, 66, 67]. Increasing evidence has suggested that acute viral infections may cause persistent lung function impairments due to pulmonary fibrosis [20].…”

Evaluation of Pregnancy, Younger Age, and Old Age as Independent Risk Factors for Poor Hospitalization Outcomes in Influenza A (H1N1)pdm09 Virus a Decade After the Pandemic

“…In 2019, Nawal et al reported the circulating strain A/Michigan/45/2015, which has replaced the strain A/California/7/2009 in India and has been associated with slightly lower mortality rates but has significantly affected the population with more comorbidities [25]. During the 2009 H1N1 pandemic, attack rates and relative risk of death were higher for younger adults [3,14] and children, whereas the elderly population was relatively immune due to previous influenza exposures in agreement with the antigen sin hypothesis [3,19]. Although fewer elderly individuals were infected during the pandemic, proportion-wise, mortality was substantially higher in this demography as compared to younger individuals [7,23].…”

“…Statistics from the onset of the pandemic in 2009 show that H1N1 predominantly affected young individuals in the age group of 10 to 30 years, constituting nearly 64% of the reported cases while elderly patients only made up about 1.1% [ 3 ]. The reason for the over-representation of young adults during the pandemic is postulated to be due to the protection offered by cross-reactive antibodies in elderly people who were born before 1950 from their previous influenza exposures [ 7 , 10 , 16 , 19 ]. In our study, the young adult age group, including pregnant women, made up 20.5% of the overall admissions, which is similar to the elderly age group at 19.7%.…”

“…Our study shows a similar age representation, with the attack rate shifting from young adults to the middle-aged and elderly age groups. The most likely explanation for this could be the building immunity among young adults [ 13 , 19 , 21 ], changes in the circulating strain of the virus [ 16 , 19 ], and inadequate vaccination rates among the middle-aged and elderly population [ 8 , 22 ]. This trend is similar to those of the previous flu pandemics in 1918 and 1968 [ 19 ].…”

“…Contrary to previous studies, radiological abnormalities were less prevalent among the study groups (30.9% of young adults, 12% of pregnant women, 48% of elderly). A possible reason for this could be an earlier presentation of the patients to the hospital or the seasonal variation in the clinical and lab spectrum seen over the multiple waves of H1N1 [ 8 , 11 , 19 ].…”