Influenza viruses and their pandemic potential remain a persistent threat to global health. The virus can rapidly progress to more severe illness resulting in hospitalization and death, especially among children and the elderly.
More than 50 million influenza infections and over 100,000 deaths from influenza occur annually. While Indigenous populations experience an inequitable influenza burden, the magnitude of this inequity has not previously been estimated on a global scale.
A new study recently published in the journal PLOS Global Public Health compared rates of influenza-associated hospitalization and mortality between Indigenous and non-Indigenous populations globally.
Generally, Indigenous populations worldwide experience higher ill health rates than non-Indigenous people. However, there is a lack of quality data from low and middle-income countries.
Literature published before July 13, 2021, was included in a systematic review and meta-analysis. Either a rate ratio (RR) comparing laboratory-confirmed influenza-associated hospitalization and/or mortality between an Indigenous population and a corresponding benchmark population was reported in eligible articles, or there was enough information to allow for this to be calculated using publicly available data.
When numerous studies were available, results were presented by nation/region and pooled by country and period (pandemic/seasonal) using a random-effects model. The I2 statistic measured inter-study variation.
Thirty-six studies (moderate/high quality) were included, all from high or high-middle-income countries. Of the 36 included studies, 28 (78%) had no age limitations, while others considered children, adults, or women of reproductive age.
Indigenous and non-Indigenous groups were assessed from the same population with the exception of one study, which compared the Indigenous people in Alaska with the non-Indigenous population in the rest of the USA, indicating a higher risk of bias. There was heterogeneity in the methods for assessing Indigenous status.
Influenza-associated hospitalization rates among Indigenous populations ranged from 0.8 hospitalizations per 100,000 person-months among Native Americans and Alaska Natives in the United States. A consistent pattern of statistically significant higher hospitalization rates among Indigenous populations compared to benchmark populations was demonstrated.
When observing pandemic influenza alone, HRRs comparing Indigenous to benchmark populations ranged from 1.4 in the United States to 16.1 in Canada. When observing seasonal influenza alone, the highest disparity was observed among infants in Auckland, New Zealand, wherein Māori children were 11.1 times more likely to be hospitalized for flu than European and other children during the winter months of 2014–2016. The lowest seasonal influenza HRR was 1.2, observed in the USA from 2001–2008.
Globally, the lowest rate of influenza-associated mortality for an Indigenous population was 0.03 deaths per 100,000 person-months observed among Indigenous Australians in the Northern Territory from 2007 to 2016. The highest Indigenous mortality rate was 1.6 deaths per 100,000 person-months among Indigenous Australians in North Queensland during the 2009pH1N1; however, this was based on only five deaths over the study period.
In conclusion, the study demonstrates that Indigenous populations from Australia, New Zealand, the United States, Canada, and Brazil endure a disproportionate burden of severe influenza, in terms of hospitalizations and/or mortality, compared with corresponding benchmark populations. This was consistent across included studies, with only two studies having rate ratio confidence intervals that crossed one.
Study authors noted, “This study provides a robust analysis of the available evidence relating to influenza hospitalization and mortality for Indigenous populations compared with benchmark populations.”
- Juliana M. Bette, Aaron L. Weinman et al. Influenza-associated hospitalization and mortality rates among global Indigenous populations; a systematic review and meta-analysis. PLOS Global Public Health. DOI: 10.1371/journal.pgph.0001294