Bloomberg photo by Daniel Acker

LISTEN: Infectious disease expert on herd immunity

CAPE TOWN- As more people recover from Covid-19 and have specific antibodies to fight off the virus, some are hopeful that if enough of the population develop resistance against the virus or develop herd immunity it will enable society to return to normal.

Herd immunity is defined as a level of population immunity at which disease spreading will decline and stop after a majority of a population have already been infected and after all preventive measures have been relaxed.

American vaccinologist and infectious disease epidemiologist from the Yale Institute for Global Health, Dr Saad Omer, said in a JAMA podcast that the cost of using herd immunity as a mainstream strategy is very high.

“Even if you try to sequester or isolate the most vulnerable the infection will get through and that’s a dangerous strategy… We can and should talk about herd immunity in the context of vaccines and not infection,” he said.

Omer was discussing that in his latest academic article, an infection-based herd immunity approach has been proposed to slow the spread of Covid-19, however, it is a strategy is fraught with risks.

The herd immunity threshold is defined as the proportion of individuals in a population who, having acquired immunity, can no longer participate in the chain of transmission.

“Assuming that less than 10% of the population has been infected so far, with an infection-induced immunity lasting 2 to 3 years, infection-induced herd immunity is not realistic at this point to control the pandemic. SARS-CoV-2 vaccines will help to reach the herd immunity threshold, but the effectiveness of the vaccine(s) and the vaccine coverage are to be seen,” said Omar.


The World Health Organization (WHO) chief Tedros Adhanom Ghebreyesus, warned world leaders last week against using the principle of “herd immunity” to stem the Covid-19 pandemic as it is scientifically and ethically problematic.

Tedros said during a press briefing in Geneva that, “herd immunity is achieved by protecting people from a virus, not by exposing them to it. Never in the history of public health has herd immunity been used as a strategy for responding to an outbreak, let alone a pandemic. It is scientifically and ethically problematic”.

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