Population density and the proportion of society that is elderly quickly emerged as significant factors in the spread of COVID-19. Social distancing has been widely used as an effective way to avoid transmission, but is complex to implement in a very densely populated city without draconian government action. 

More than 55 percent of the world's population is thought to live in urban areas, and that figure is predicted to rise to 68 percent over the coming decades, giving viruses the opportunity to quickly spread in many parts of the planet. 

Viruses are also likely to have particularly devastating effects among elderly populations.  It is now known that older age and underlying health conditions are risk factors when a person is infected with Covid-19.

So where in the world are the most densely populated, most elderly cities? Some of the following have already been associated with large outbreaks of the coronavirus.

Osaka/Kobe/Kyoto (16,592 people per square mile), Sapporo (12,981 ppsm), and Tokyo (12,296 ppsm) in Japan.

After avoiding the devastating outbreaks seen in Wuhan, Italy and Spain, Japan's Prime Minister Shinzo Abe last week declared a national state of emergency after cases surged in Tokyo.

Japan has very high population density as well as the oldest population in the world, with 28.2% of all Japanese aged over 65.  Partly due to its aging population, Japan already has the highest death rate from diseases of the respiratory system in the world, despite the fact it has a well functioning healthcare system.

Athens, Greece

This ancient city has a population density of 13,953 ppsm, and 21.8% of all Greeks are aged over 65.  Greece is another country that already has extremely high rates of respiratory illness. However, early government action seems to be responsible for its having one of the lowest rates of infection and deaths in Europe.

Madrid (13,430 ppsm) and Barcelona (12,579 ppsm) in Spain 

Spain has both high population density (Madrid is among the most densely populated metropolitan areas in Europe) and a very elderly population, with 19.1% of all Spaniards aged over 65.   This is one reason Spain has been one of the countries worst-hit by Covid-19 so far.

London in the United Kingdom

London has a population density of 13,210 ppsm, and 18.3% of its population is aged over 65. London has emerged as the epicentre of Covid-19 in the UK, with deaths in the capital accounting for a large proportion of the overall nationwide toll.

Shenzhen (44,464 ppsm), Shanghai (34,718 ppsm), Beijing (29,827 ppsm), Tianjin (27,158 ppsm), and Shenyang (24,013 ppsm) in China

These cities are among the most densely populated cities in the world.  At the same time, 16.4% of China’s population is aged over 65. However, massive government intervention in China seems to have resulted in relatively low outbreaks in these cities and across the country. Nationally, infection rates conformed to the pattern of increasing with age.

(Claims circulating on social media that Shanghai and Beijing have been unaffected by COVID-19 are false, according to this fact-check.)

Seoul/Incheon in South Korea

Seoul has extremely high population density of 43,208 ppsm, and at the same time 15.1% of South Korea’s population is aged over 65.

The government there reacted quickly after the outbreak in Wuhan, instigating widespread testing even before the country’s biggest outbreak linked to a 61-year-old woman who attended a service at the Shincheonji megachurch in Daegu, about 240 kilometers southeast of Seoul. Testing and tracing are credited with containing the virus in South Korea without lockdowns.

Some think that the Covid-19 virus is likely to prefer colder temperatures and lower humidity, though there is no conclusive evidence of this as yet.  If true, it could be very good news for some of the most densely populated cities in the world in India, Nigeria and Pakistan, which all experience high temperatures over the coming months.

The scale of government action, however, seems to be the key to controlling outbreaks in the most vulnerable countries.

Postscript: A 106-year-old British woman is being celebrated for fighting off a COVID-19 infection. Connie Titchen is the oldest known survivor of the virus.

Shannon Roberts is Co-Editor of Demography is Destiny, MercatorNet’s blog on population issues.