Parts of Asia reacted quickly to the threat and largely started social distancing earlier on. But researchers are also examining other factors, including differences in genetics and immune system responses, separate virus strains and regional contrasts in obesity levels and general health.
What are the numbers?
China, where the virus emerged late last year in Wuhan, has recorded fewer than 5,000 deaths, which translates to three deaths per million inhabitants. Japan has around seven per million, Pakistan six, South Korea and Indonesia five, India three and Thailand fewer than one per million. Vietnam, Cambodia and Mongolia say they have recorded zero covid-19-related deaths.
Compare that with about 100 deaths per million in Germany, about 180 in Canada, nearly 300 in the United States and more than 500 in Britain, Italy and Spain.
Scientists at Japan’s Chiba University plotted the trajectory of the virus across the world and said they noticed stark regional disparities.
“That means we need to take into consideration regional differences first, before analyzing what policies and other factors are affecting the spread of infection in any given country,” said Akihiro Hisaka of the university’s Graduate School of Pharmaceutical Sciences.
The conventional wisdom
The baseline assumption, at the moment, is that the virus — officially SARS-CoV-2 — mutates the way all viruses do and is just as innately contagious and lethal in one part of the world as in another.
“We are all facing the same bug with the same general arsenal of immune responses,” said Jeffrey Shaman, an epidemiologist at Columbia University. “There are differences in testing, reporting, control from country to country. And there are differences in rates of hypertension, chronic lung disease, et cetera, on a country-by-country basis.”
Part of the reason for the high number of deaths in the United States and Western Europe may lie in an initial reluctance to react to an epidemic that seemed distant and unthreatening. In Asia, meanwhile, previous experience with the SARS and MERS epidemics enabled much faster responses to the new threat.
Taiwan, for example, has been widely praised for its speedy response to the epidemic, including early screening of air passengers from Wuhan. South Korea built a massive program of testing, tracing and isolating patients.
But in Japan and India, two very different countries, the relatively low death toll has baffled many scientists. Similar mysteries have emerged from Pakistan to the Philippines.
Weather and culture a reason?
Hot and humid weather could be a factor in places such as Cambodia, Vietnam and Singapore. Several studies have suggested that heat and humidity can slow, although not stop, the spread of the virus, just as is seen with influenza and with coronaviruses that cause common colds. But some equatorial countries, including Ecuador and Brazil, have seen many cases and deaths linked to covid-19.
Demographics also play a role in regional disparities. Africa’s generally younger population may have been more resistant than northern Italy’s older communities, for example.
In Japan, which has the world’s oldest population, different reasons are being explored.
There is a widespread belief in Japan that good hygiene and habits, like wearing masks and avoiding handshakes, helped slow the spread of the virus, while universal health care and the country’s emphasis on protecting the elderly may have lowered the death toll.
What about different strains?
Research by a team at Cambridge University showed how the virus mutated as it left East Asia and traveled to Europe, noting the possibility that the initial strain may have been “immunologically or environmentally adapted to a large section of the East Asian population”…