By Dr Dominic Pimenta

In early February we heard reports of an increasingly virulent pathogen marching inexorably across the world, from Wuhan to Iran to Tenerife to Italy to London. We weren't sure exactly how deadly it was, or how many people might be infected, or what we should do about it. Scientists and politicians were at odds, and the widespread conversations ranged from dubious scepticism to nail-biting concern. The idea we should lock down to combat the spread, when it became clear that cases were rising locally and hospitals and deaths were rocketing, was equally controversial.

The hospitals were initially overwhelmed. We had some of the worst excess deaths in the world, and all too quickly we were looking back and wondering if we could've done things differently.

Six months later, it seems we have gone the long way round to intellectual nowhere. Here we are again, watching hospitalisations and deaths creep inexorably upwards again, edging closer to that critical limit in the North West once more. And once again Sage and politicians are at odds about what to do, with widespread division and distrust among the general public.

On both sides of the Atlantic, the science of what we should do next appears fractured. Last week, the 'Great Barrington Declaration' was announced with a lot of pomp and circumstance. Its signatories are all outspoken academic sceptics of lockdown measures. Their main thrust is that further lockdowns should be avoided. Instead, we should go pursue 'focused protection' of those at most risk, while everyone else goes back to normal life.

It's a tantalising prospect, especially as we face lockdown once more. Across the Atlantic, the White House is reportedly embracing the same thinking. But it's a proposal that flies in the face of months of global public health measures.

So, is the science really divided? In short, no. Under the PR, through the fog of data, the fundamentals have not really changed. The scientific consensus remains the same.

In a letter published today in The Lancet, leading epidemiologists, public health academics, virologists, biologists, healthcare charities and doctors from around the world reaffirmed this consensus. It's titled the John Snow Memorandum. It addresses this manufactured divide in scientific opinion as exactly that – a "dangerous fallacy unsupported by scientific evidence". I am a signatory to the letter in my capacity as a former covid ICU medic and chairman of the Healthcare Workers Foundation (Heroes).

These are our views on the pandemic. Firstly, lockdowns are a last resort. The measure has undoubted impact on the economy and mental health. However, these effects are mitigated by proper use for a time-limited period, to establish effective 'pandemic control systems'. These are systems which, in the UK at least, we didn't establish the first time. We squandered our time over the summer with malfunctioning apps and failing test and trace.

There is a critical threshold at which these systems will work again, but we are currently well above this. Bringing cases back into this threshold, and overhauling this system, is the best strategy to suppress the virus and return to near-normal life, as they are doing in New Zealand.

Secondly, the alternative proposal from the Great Barrington Declaration is deeply flawed – scientifically, ethically and practically. The basic premise of generating herd immunity in a lower risk population has no basis in the current scientific knowledge about covid. There is no evidence that we can generate lasting immunity from natural infection, and we have already started to see documented cases of re-infections.

Worse, even in a population at low risk of death, we don't know the long-term health effects on morbidity. Long covid affects a significant proportion of mild cases with long-term debilitating health conditions – fatigue, heart and brain problems, and inflammatory syndromes in children.

The vulnerable proportion of the UK is approximately 30%. So asking this portion to shield in 'focused protection' immediately hits a few massive stumbling blocks. The economic impact of removing a third of the population of society in the long-term would be equally disastrous as any national lockdown measure and the shielding wouldn't be limited to just the 30% – many would be in intergenerational homes, workplaces or childcare where the true number that would have to effectively shield would be far higher.

It isn't practical to shield 22m people from everybody else. How could this possibly be enforced? We have already seen cases rising in the younger at-risk groups and spreading to the older population. The most likely real-life outcome of 'focused protection' would be failure, with the resultant colossal loss of life and economic impact as we try to lockdown with a much higher level of community virus.

And even if it did work, it would be for nothing. Herd immunity, no matter the other problems with it, cannot be generated at all if such a high proportion of the population aren't infected.

None of these questions have been answered, and yet as a strategy – despite the risks of hundreds of thousands of unnecessary deaths and massive morbidity – it has been championed as a viable and 'scientific' option on both sides of the Atlantic. It is anything but.

Whatever we decide to do, public opinion is vital in ensuring the success of any measure to control the virus. John Snow is considered the founder of modern public health science, after studying and successfully halting a cholera outbreak in London. He demonstrated that there are real-life interventions into the spread of disease which can save lives. With this memorandum the latest generation of the global community of public health scientists continue that spirit.

Taking effective, clear and evidence-based action is the only way out of this pandemic. Let's hope it isn't too late.

Dr Dominic Pimenta is a London-based doctor and writer. His book Duty of Care, is available now. All royalties from book sales go to Heroes, a charity supporting healthcare workers. You can follow him on Twitter here. Scientists and qualified healthcare professionals can sign the memorandum here.

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