The World Health Organization on Monday warned against suggestions that herd immunity might be a realistic strategy to stop the coronavirus pandemic, saying such an approach was “simply unethical”. Herd immunity occurs when majority of a population becomes immune to a disease through vaccinations or through the mass spread of a disease.

At a media briefing, WHO Director-General Tedros Adhanom Ghebreyesus said that health officials typically aim to achieve herd immunity via vaccination. He added that to obtain herd immunity from a highly infectious disease such as measles, about 95% of the population must be immunised. Similarly, Tedros said, for polio the threshold is about 80%. The percentage of a population who need be to be vaccinated to reach herd immunity is calculated using the basic reproductive rate (R0).

“Herd immunity is achieved by protecting people from a virus, not by exposing them to it,” the health body chief said. “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.”

Tedros said that too little was known about immunity against the coronavirus to assess if herd immunity was even achievable.

“Most people who are infected with the virus that causes Covid-19 develop an immune response within the first few weeks, but we don’t know how strong or lasting that immune response is, or how it differs for different people. We have some clues, but we don’t have the complete picture. There have also been some examples of people infected with Covid-19 being infected for a second time. Second, the vast majority of people in most countries remain susceptible to this virus. Seroprevalence surveys suggest that in most countries, less than 10% of the population have been infected with the Covid-19 virus.”

— WHO chief Tedros Adhanom Ghebreyesus

Researchers argued that allowing the infection to spread in populations that are not vulnerable will help build up herd immunity and called it a more realistic way to stop the pandemic.

“Allowing a dangerous virus that we don’t fully understand to run free is simply unethical,” Tedros said at the media briefing. “It’s not an option.”

He also highlighted that countries had reported record-high daily figures of new coronavirus cases to the United Nations health agency for the last four days, citing rise in Europe and the Americas in particular. “There are no shortcuts and no silver bullets,” the WHO chief said. “The answer is a comprehensive approach – using every tool in the toolbox.”

Over 100 vaccines are being developed around the world to tackle the coronavirus pandemic. The global coronavirus count has crossed 3.77 crore and the toll rose to 10,78,868, according to Johns Hopkins University. The number of recoveries is over 2.61 crore.

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