Covid-19 cannot be allowed to “rip” through the population, the Prime Minister has said.
Alluding to the concept of herd immunity, Boris Johnson said this strategy would see an “intolerable” death toll from Covid-19 and put such a “huge strain” on the NHS that it would not be able to treat any other condition.
He said the idea of letting the virus “take hold” among the young and fit while shielding the elderly and vulnerable was “no answer”.
It comes as the World Health Organisation (WHO) said that herd immunity for Covid-19 is “unethical” and “not an option”.
Herd immunity occurs when a large portion of a population becomes immune to a disease.
The concept is gaining popularity among some, including a group of scientists who have signed the so-called Great Barrington Declaration.
The declaration, which is earning thousands of signatures from medical professionals, academics and the general public, calls for a herd immunity approach to tackling the Covid-19 pandemic while protecting the most vulnerable populations.
It suggests that people who are less vulnerable to the effects of Covid-19 should be allowed to return to normal life.
In his speech to the Commons, Mr Johnson said: “There are those who think that the patience of the public is now exhausted, that we should abandon the fight against Covid, stand aside, let nature take her course and call halt these repressions of liberty.
“And of course I understand those emotions, I understand the frustration of those who have been chafing under the restrictions, the sacrifices they’ve made.
“But if we were to follow that course and let the virus rip, then the bleak mathematics dictate that we would suffer not only an intolerable death toll from Covid, we will put such a huge strain on our NHS with an uncontrolled second spike that our doctors and nurses would be simply unable to devote themselves to other treatments for cancer, heart disease, hundreds more that have already been delayed.
“And that would be delayed again with serious long term damage to the health of the nation.
“And I’m afraid it is no answer to say that we could let the virus take hold among the young and fit while shielding the elderly and vulnerable, because the virus would then spread with such velocity in the general population that there would be no way of stopping it from spreading among the elderly.
“And even if the virus is less lethal for the under 60s there will still be many younger people for whom, alas, it remains lethal.
“We don’t want to go back to another national lockdown.
“We can’t let the virus rip.
“And so we’ve followed since June, a balanced approach.”
It comes as WHO director general Dr Tedros Adhanom Ghebreyesus told a press briefing: “There has been some discussion about the concept of reaching so-called ‘herd immunity’ by letting the virus spread.
“Herd immunity is a concept used for vaccination, in which a population can be protected from a certain virus if a threshold of vaccination is reached.
“For example, herd immunity against measles requires about 95% of a population to be vaccinated.
“The remaining 5% will be protected by the fact that measles will not spread among those who are vaccinated.
“For polio, the threshold is about 80%.
“In other words, 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.
“Firstly, we don’t know enough about immunity to Covid-19, most people who are infected with the virus 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.
“There have also been some examples of people infected with Covid-19 being infected for a second time.
“Secondly, 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.
“Letting Covid-19 circulate unchecked therefore means allowing unnecessary infections, suffering and death.
“Although older people and those with underlying conditions are most at risk of severe disease and death, they aren’t the only ones at risk.
“People of all ages have died.
“Thirdly, we’re only beginning to understand the long-term health impacts among people with Covid-19.
“I have met with patient groups suffering with what is now being described as long Covid to understand their suffering and needs so we can advance research and rehabilitation.
“Allowing a dangerous virus that we don’t fully understand to run free is simply unethical.
“It’s not an option.”
Dr Tedros added that there are “no shortcuts, and no silver bullets”, saying that countries need to use “every tool in the toolbox” to tackle the virus.