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London, Oct. 15 (PTI): Managing Covid-19 by allowing herd immunity to develop in low-risk populations while protecting the most vulnerable is "a dangerous fallacy unsupported by the scientific evidence," warn an international group of 80 researchers in an open letter.
The letter, published in The Lancet journal, referred to by its authors as the John Snow Memorandum, noted that any pandemic management strategy relying upon the population to develop immunity from natural infections for Covid-19 is flawed.
In the face of a second wave of infection in several parts of the world, the scientists including Devi Sridhar from the University of Edinburgh in the UK, said there is currently renewed interest in herd immunity approaches allowing a large uncontrolled outbreak in low-risk populations while protecting the vulnerable.
While some have argued this approach could lead to the development of infection-acquired immunity in the low-risk population, which will eventually protect the vulnerable, the researchers explained such uncontrolled transmission in younger people risks significant ill-health and death.
Based on evidence from many countries, the scientists said it is not possible to restrict uncontrolled outbreaks to certain sections of society, adding that it is "practically impossible" and "highly unethical" to isolate large swathes of the population.
While special efforts to protect the most vulnerable are essential, they said these must go hand-in-hand with multi-pronged population-level strategies.
"Effective measures that suppress and control transmission need to be implemented widely, and they must be supported by financial and social programmes that encourage community responses and address the inequities that have been amplified by the pandemic," they wrote in the letter.
"Continuing restrictions will probably be required in the short term, to reduce transmission and fix ineffective pandemic response systems, in order to prevent future lockdowns," the researchers said.
According to the scientists, the restrictions can effectively suppress the number if infections to low levels that allow rapid detection of localised outbreaks.
They said such measures can also compliment rapid response through efficient and comprehensive testing, contact tracing, isolation and support systems.
"Protecting our economies is inextricably tied to controlling Covid-19. We must protect our workforce and avoid long-term uncertainty," they said.
The researchers cautioned that there is currently no evidence for lasting protective immunity to SARS-CoV-2 after natural infection.
They said this waning immunity as a result of natural infection would not end the Covid-19 pandemic but instead result in repeated waves of transmission over several years.
According to the scientists, vulnerable populations are at risk for the indefinite future, as natural infection-based herd immunity strategies would result in recurrent epidemics, as seen with many infectious diseases before mass vaccination.
So they called for controlling the spread of the virus until the population can be vaccinated.
Natural infection-based herd immunity approaches risk impacting the workforce as a whole and overwhelming the ability of healthcare systems to provide acute and routine care, the researchers warned.
They said clinicians still do not understand who might suffer from 'long Covid' in which the symptoms linger for weeks.
"The evidence is very clear: controlling community spread of Covid-19 is the best way to protect our societies and economies until safe and effective vaccines and therapeutics arrive within the coming months," the scientists wrote.
"We cannot afford distractions that undermine an effective response; it is essential that we act urgently based on the evidence," they concluded.