4 factors explain countries’ COVID outbreak severity

Four things—median age, obesity rate, island geography, and border measures—account for more than 70% of the variation in nations’ COVID-19 outbreak rates.

The number 4 painted in red on a blue wall

Differences among nations' COVID-19 outbreaks are due to a country's median age, its obesity rate, its border-closure measures, and whether or not it is an island or mainland nation, according to a new analysis of pandemic data.

“This research helps to explain the longstanding question of why the pandemic has struck some nations more severely than others, and in particular why more developed nations have tended to have more severe outbreaks,” says Ethan Ludwin-Peery, a doctoral candidate in New York University's psychology department and one of the authors of the paper, a preprint posted on medRxiv.

The paper's authors, however, note that geography plays an uneven role in obesity rates and border closures. For example, while the researchers found a relationship between obesity rates and COVID-19 cases in mainland nations, the same relationship did not appear in island nations.

Similarly, border closures had a different impact on mainland and island nations. Island nations showed a strong association between significant border restrictions and lower numbers of coronavirus cases, but this relationship did not hold for mainland nations, suggesting the efficacy of border closures is limited to island countries.

However, the researchers add, the study illuminates forces that may have been previously overlooked–even if they were not universally applicable.

Obesity has been found to increase the severity of COVID-19 cases, but obesity rates have not generally been seen as a major factor in explaining the differences in COVID-19 rates worldwide,” adds coauthor Joseph Fraiman, an emergency room physician at Louisiana State University's Lallie Kemp Regional Medical Center.

“The low rates of COVID-19 in East and Southeast Asia have typically been credited to aggressive COVID-19 policies, which certainly did reduce COVID-19 transmission. However, the relatively low obesity rates in these countries may further explain the dramatic differences in COVID-19 rates when compared with many European nations.”

The study's authors note that early on in the pandemic, the most severe COVID-19 outbreaks occurred in some of the most developed countries—contrary to past spreads of infectious diseases, which have historically taken a greater toll on poorer and less-developed nations, due, in part, to less access to healthcare.

To better understand this initial phenomenon, measured by COVID-19 cases per one million among a country's population, they explored several potential explanatory variables: GDP per capita, population density, percentage of urban population, median age, obesity rate, geography (mainland or island nation), and border-closure policies (ranging from no border closure to strict closure policies).

The researchers used publicly available data, obtained from multiple sources, including ourworldindata.com, the Nations Online Program, the CIA World Factbook, and the World Bank, to study nearly 200 countries.

Border closure ratings, drawn from the Oxford COVID-19 Government Response Tracker, used a scale of 0 to 4, with 0 being no border restrictions and 4 being the most restrictive. For example, a rating of “3” indicates a country that has a ban on international travel from high-risk regions.

Overall, the results showed that four factors—median age, obesity rate, island geography, and border measures—explained more than 70% of the variation among countries' COVID-19 rates. Notably, these factors remained significant even when controlling for measures of wealth and development, such as national GDP.

“In fact, taking into account a country's GDP barely changes the influence of these factors at all,” says Ludwin-Peery.

Source: NYU

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