By Dr. Zain Chagla, Dr. Isaac Bogoch and Dr. Sumon Chakrabarti
HAZEM BADER/AFP VIA GETTY IMAGES
This past Friday, Dr. Michael Ryan, executive director of the World Health Organization’s Health Emergencies Programme, noted that in the current context, COVID-19 “elimination” in most places is unlikely. Elimination refers to zero cases of COVID-19 in a particular geographic area, such as a country, while eradication refers to bringing the global burden of cases to zero, which would be extremely difficult to achieve. Exceptions to this mainly included such geographically isolated countries as New Zealand that have been able to drastically reduce COVID cases, which is not possible in other areas of the world; however, even in these situations, as borders reopen, there will likely be a resurgence.
What does it take to get an infectious disease eliminated? There are four major principles to eliminate an infection within the human population:
• A biologic intervention that prevents transmission of the disease in nearly all individuals, for example, a vaccine.
• A diagnostic test that picks up the vast majority of, if not all, cases.
• A surveillance system to detect cases as the disease nears elimination and afterwards to ensure there is no rebound.
• No other place for this infection to hide, and then reinfect humans, such as an animal “reservoir” — a disease that exists naturally among animals and can be transmitted to humans cannot be eliminated by defeating it in human hosts alone.
Smallpox fit the prototype of this model. A viral disease that led to a rash similar to chickenpox, smallpox caused significant suffering globally, leading to the death of up to 30 to 50 per cent of individuals affected. A significant reduction in the global burden of smallpox was due to the work of Edward Jenner, who derived the first vaccine from a related virus called cowpox (its scientific name was Vaccinia — the root word of the word “vaccine”). In the 1950s, through a global effort by the World Health Assembly, a smallpox eradication campaign took place. Two decades later, for the first time in recorded history, the world saw the eradication of an infectious disease.
WELLCOME LIBRARY, LONDON
Given the global burden of COVID-19, even if a single area of the world were to eliminate the disease, it would be very likely to be reintroduced once travel resumes, as was seen recently in New Zealand.