Those most vulnerable to the coronavirus are the elderly and people with serious underlying illnesses such as diabetes or cancer. But people who lack access to healthcare, or live in a setting where sanitary systems are not adequately developed, can also be at risk.
Cecilia Tacoli, Principal researcher, Human Settlements, for International Institute for Environment and Development (IIED), said social distancing is "unrealistic" for the world's poor.
"Low-income settlements in cities of low- and middle-income nations are typically very densely populated, with very inadequate provision of basic infrastructure, [water and sanitation] and services [health services], all of which encourage the spread of communicable diseases," she said.
"The vast majority of the urban poor do not have access to formal employment but rely on casual jobs which only provide meagre incomes. This means that current prescriptions - from washing hands frequently to social isolation and working from home - are unrealistic."
Tacoli added that although it is clear that the elderly are most at risk globally, the vulnerability of older women could prove disastrous.
"It is worth keeping in mind that throughout the world about three billion people live in such settlements, and that in many cities they are the majority of the population. Older people, especially women, often play a very important role looking after children and ill relatives. These two observations are critical in considering worst-case scenarios," she said.
"The high density of people and the inability to create effective social distancing are key factors in making transmission more likely," said Eric Fevre, a professor of veterinary infectious diseases at the University of Liverpool. Nor are slum communities isolated from the rest of the city, leaving them as vulnerable to the disease as elsewhere.
"In addition, I would add that such settlements are at risk because the people who live there have to be able to access other richer parts of the city for work," Fevre told Al Jazeera.
Many residents of such settlements live in extended families but have only a few rooms. Some may have only one. And if the area itself were quarantined, the situation could even become dangerous because any illness could spread quickly through the densely populated area.