Photo report by ITV News correspondent Tom Clark
The term “herd immunity” used to be a technical term rarely used outside of the disciplines of epidemiology or vaccination.
But it is now one of the most controversial concepts of the Coronavirus pandemic.
It’s a simple concept: When a population is exposed to a virus, people become immune and can no longer spread the insect to others.
Once a certain threshold is reached, there will not be enough people exposed to the virus, and that’s herd immunity.
The general rule is that approximately 70 to 80% of the population must be immune to a virus like SARS-CoV-2 to stop the spread (for highly contagious viruses like measles, the number can be higher – about 95%).
But what if in the real world we got to herd immunity at much lower levels.
Last March, theoretical epidemiologist Sunitra Gupta published an analysis indicating that herd immunity to COVID-19 may be more than 20% given that many of us appear to be resistant to infection, possibly due to previous exposure to related coronaviruses.
Her paper has been widely criticized by other epidemiologists, especially those who advise governments.
It was based on mathematical analysis, not real-world observations.
Moreover, by the time it was published, the virus had started spreading rapidly among residents of care homes.
It became clear that the policy based on herd immunity – allowing natural resistance to build up among those at low risk while protecting the vulnerable – would have been a disaster based on our failure to protect those most at risk.
But what if she and the other disease model maker were right? And what could that mean for how the outbreak is managed from now on?
In countries such as Brazil and Sweden, and parts of the United States that have not pursued stringent lockdown strategies, there is evidence that the outbreak has now reached some kind of natural peak, as cases begin to decline.
However, tests in the population indicate that 20% – at most – have antibodies to the virus.
All are severely affected, with an estimated 1 in 500 people dying in Manaus, Brazil, but the outbreak appears to be declining with well below 70% of herd immunity.
Since we now have a greater capacity to test for the virus, and must be more prepared to protect the vulnerable, is it time to reconsider the idea of herd immunity?
Ms Gupta said: “We can’t look at our response just along the single axis of how to keep the coronavirus under control.
“The strategy that the welfare state should take at this point in time is to protect the vulnerable and allow the virus to spread among those who are not in danger of death.”
“We have to think about who is paying the price for it.
“We put in place a system that does not protect the vulnerable, and we are now asking those economically vulnerable to pay for it.”
Her views have divided the scientific community, and while few of them disagree with the theory, they argue that we do not know enough to ensure that the retreat and allow the development of immunity will work in practice.
Dr Swamya Swaminathan, chief scientist at the World Health Organization, said: “Even if 1% of infected people die, this adds up to a large number of people if you look at the world’s population.
“We have to talk about herd immunity in the context of a vaccine.”
Moreover, it is not entirely clear what ‘immunity’ to SARS-CoV-2 looks like.
Strong evidence has emerged that antibodies to the virus decline over time.
More cases of infected people are now appearing more than once.
Some argue that this is good evidence that permanent herd immunity will not develop at all – and that it may challenge developing a vaccine.
Other experts argue that other coronaviruses cause frequent infections, but only mild illness, and that soon, this new coronavirus will behave the same way once we are exposed to it.
For now, the debate is still largely academic.
But since the true costs of a severe lockdown begin to feel not only the economy but also the long-term health of people, that’s a debate we’ll only hear more about.
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