Coronavirus and Temperature
The COVID-19 disease, caused by the novel coronavirus, is the most serious health crisis since the Spanish flu of 1918, which is estimated to have killed between 50 million and 100 million people worldwide. By the latest count (March 29), the disease had spread to over 177 countries, with more than 630,000 cases reported and 30,000 recorded deaths. These numbers are increasing exponentially at present and the cases and deaths reported are both believed to be under counted. Deaths are strongly concentrated in the older population (aged 65 and over) and among those with serious pre-existing conditions, according to a study by Chinese researchers and extensive epidemiological data from South Korea and Italy. Although COVID-19 is now officially a pandemic, its spread across the world remains very uneven, with China reporting 59 cases per million, and Italy—the epicenter of the crisis at time of writing—over 1530 cases per million, while several countries with warmer climates, such as the Philippines, report fewer than 10 cases per million. This uneven distribution has led to both fear and hope. Fear, because the disease might still spread virulently to Africa and other poor nations, where very few tests have been conducted and where medical systems are least equipped to cope. Hope, because the slower spread of the virus in hot climates might be an important signal that the disease will ease with the coming of spring and summer in the hardest-hit temperate zones. This has been the case with other strains of corona virus in the past, such as those that are at the root of ordinary flu. Though written in the ‘fog of war’, this note attempts to evaluate the importance of temperature in accounting for the spread of the virus. We attempt this despite the fact that reported cases are a very imperfect measure of the spread of the virus, mainly because of major differences in the frequency of tests. For example, based on the limited information available about testing, poor countries, which tend to be in warmer climates, test less and almost certainly tend to report fewer cases for that reason.