The analysis by researchers from Spain and Peru reveals that high altitude confers significant protection from coronavirus disease (COVID-19) infection and death – independent of the distance from the pandemic epicenter, population density, or poverty levels. The study is currently available on the medRxiv* preprint server.
More than 700 thousand people around the world have already lost their lives as a result of the COVID-19 pandemic caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). It is evident that some countries have been hit harder by the disease than others.
Although initially spared, COVID-19 cases have recently been rising sharply in Latin American countries. Nonetheless, due to underreporting issues and the relative scarcity of detailed data, only a handful of studies have investigated the dynamics and specific characteristics of the pandemic in South America.
But despite such information shortcomings in the early stages, accumulating data now makes it possible to conduct much more detailed epidemiological analyses, which are necessary to inform policies intended to protect the populations at the higher risk of contracting the disease.
In this new study, researchers from the National Science Council (Barcelona), Instituto Nacional de la Salud Carlos III (Madrid) and Institute for Biocomputation and Physics of Complex Systems (Zaragoza) in Spain, as well as from the Universidad Peruana Cayetano Heredia (Lima) in Peru, have taken an ecological approach to describe the current state and dynamics of the pandemic in Peru.
District-level map of case and death rates in Peru, normalized for population density. Cumulative COVID-19 case and death rates per population density [cases or deaths/(persons/Km2)] on each of the indicated cut-off dates are mapped at the district level. Heatmaps and their equivalencies are specific for each date. The numbers indicate the upper limits of value range. Blue circles are indicators of the Lima metropolitan region.
Detailed temporal and spatial analyses
Although prior studies have already hinted that altitude may be a protective factor from COVID-19, this retrospective analysis is the first to utilize an extensive longitudinal national database covering all COVID-19 cases and deaths registered in Peru until July 17, 2020.
In order to correct for population density, which has a tendency to be substantially higher on the coastal lowlands, the researchers have normalized case/death counts by population density and per million inhabitants in all districts.
Moreover, they have taken into account the prevalence of non-transmissible diseases (described by prior surveys) as a proxy for potential co-morbidities associated with the incidence of infections and fatal outcomes.
High altitude as a protective factor
"Our most relevant finding is a significant association between life in high altitude and a lower risk of COVID-19 contagion and death from the disease", study authors state in their medRxiv* paper.
The study also provides evidence that the recent surge of cases in high-altitude districts in Peru may be explained by the inrush of migrants from large urban centers to high-altitude districts via a specific route – overriding, in turn, the shielding effect possibly conferred by high altitude to the inhabitants of those particular districts.
The findings further reveal that the normalized death rate from COVID-19 is significantly correlated with the prevalence of high blood pressure and cholesterol levels, as well as low altitude. However, COVID-19 death rates are not significantly correlated with population density, despite an observed trend.
Finally, the protection by altitude was found to be independent of poverty indexes, which means altitude confers protection from COVID-19 incidence and death that is not counterbalanced even by high poverty levels.
Multisystemic adaptations to hypobaric hypoxia
"We favor the view that long-term high altitude habitation/exposure protects from severe respiratory viral diseases, including COVID-19, through multiple mechanisms prevalent in residents or genetically selected populations adapted to chronic hypobaric hypoxia", study authors put their findings into context.
Such mechanisms include anatomical, physiological, and immune adaptations. Furthermore, it has been argued that environmental factors (high ultraviolet radiation, low temperatures, or low humidity) could contribute to a diminished transmission of SARS-CoV-2 at high altitude.
Still, translating this knowledge to develop effective treatments against COVID-19 will be challenging, as protective effects may necessitate long-term, multisystemic adaptations. At the same time, there may also be manifold downstream consequences of manipulating various components of the hypoxia response.
And caution is still needed, as adaptations to high altitude may indeed confer a degree of protection from SARS-CoV-2 and COVID-19, but not immunity per se; hence, all appropriate protective steps have to be followed diligently.
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.