Social inequalities in infectious diseases

In 2017, one of the authors (S.-E.M.) wrote a short perspective article in a special issue on global health for the Norwegian Medical Journal [1] that had two purposes: (a) to give a short review of the literature on the associations between socio-economic status (SES) and mortality in the 1918 and 2009 influenza pandemics, and (b) to review international pandemic influenza preparedness plans to see whether they included ideas for how to reduce social disparities in pandemic outcomes. The paper particularly studied whether the plans defined vulnerable groups socially and not only medically, and whether (non-)pharmaceutical interventions were indicated for groups such as families living below the local poverty line. It also studied whether models of the potential impact of (non-)pharmaceutical interventions on pandemic outcomes included individual or area-level SES indicators (e.g. income, education, deprivation). Results of this 2017 review showed that reducing social inequalities in pandemic disease burden was a neglected factor in (influenza) pandemic preparedness plans for the EU, including all 28 member states, as well as Iceland, Norway, Switzerland, Turkey, Macedonia, the USA, Canada, Australia and the World Health Organization (WHO) [1]. This was surprising for several reasons. First, studies cited in the 2017 review showed that the poorest suffered the highest risks of infection and of having a severe disease in both the 1918 and 2009 influenza pandemics. Second, the UN Sustainable Development Goals include reducing social inequalities (goal 10), eradication of poverty (goal 1) and ensuring good health for all (goal 3) by 2030. Finally, there are increasing inequalities in income and wealth both within and between nations [2]. The lack of a social justice perspective was also mentioned in the literature before the 2009 pandemic [3–5], and several studies showed that there were substantial social inequalities in the 2009 pandemic influenza outcomes [6,7]. A recent systematic review and meta-analysis of nine studies of the 1918 pandemic and 35 of the 2009 pandemic also documented a clear role for SES in the disease burden (infection, hospitalisation or mortality). A random-effects analysis found a pooled mean odds ratio of 1.4 (95% confidence interval (CI) 1.2–1.7), comparing the influenza outcomes in the lowest to the highest SES. Further, of 14 studies on the 2009 pandemic that included data on both medical and social risk factors, eight demonstrated an independent impact of SES on infection, hospitalisation and mortality risks after controlling for medical risk factors [8]. These results show how persistent social risk factors are, even though the mechanisms and types of social vulnerabilities leading to social disparities in pandemic outcomes may differ over time. Social inequalities might be neglected or forgotten in (influenza) pandemic preparedness for several reasons, and we offer several suggestions here. Most of the plans are written by Western highincome countries where typically the focus is instead on reducing social inequalities in mortality from non-communicable diseases, such as cardiovascular disease, coronary heart disease (CHD) and cancer. It might be believed that once one controls for medical risk factors, everything is socially neutral, Social inequalities in infectious diseases