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expert reaction to SAGE document looking at a segmentation strategy

SAGE have published a document which considers the scientific aspects relating to a strategy that would segment the population into broad age and risk groups, for example adding further restrictions to those over 60 or who are otherwise identified as vulnerable, while not attempting to restrain transmission in younger people.


Dr Stephen Griffin, Associate Professor in the School of Medicine, University of Leeds, said:

“This paper from SAGE eloquently substantiates the arguments against a segmentation policy where a somewhat ill-defined “vulnerable” section of the population are effectively sealed off from the rest of society. The idea is that the remainder of society allow SARS-CoV2 to spread amongst them, generating herd immunity that will eventually protect the entire population. This is a core principle of the Great Barrington declaration, which has attracted a large amount of media attention since its inception a few weeks ago. This approach has had considerable appeal to many seeking to minimise the impact of the pandemic for a variety of reasons, and has sadly spilled over into the political arena. However, the concept is ultimately flawed and is in no way supported by current scientific understanding.

“Societal segregation is arguably ethically unsound, identifying those in the “vulnerable” cohort is a logistical non-starter, and it is likely that immunity from natural SARS-CoV2 infection is short-lived. Moreover, to be viable, herd immunity needs to pervade the entire population and we now understand that a significant number of younger and otherwise “healthy” people in fact endure severe and long lasting complications from SARS-CoV2 infection. To allow a strategy such as this to influence any sort of pandemic-related policy would therefore be a catastrophic mistake and it is both upsetting and troubling to see politicians endorsing it.

“Lastly, it is important to distinguish the segregation strategy here from the policy of shielding that we saw in the spring. Shielding provided advice, logistical and also legislative support for people with health conditions that render them extremely vulnerable to COVID. Importantly, this support allowed people to take additional precautions without fear of losing their jobs, or having to expose themselves to certain scenarios. Critically, shielding comprised part of a suppression strategy, thereby eventually leading to the pausing of the policy in August. Sadly, the current resurgence of the virus within the UK places us yet again in the difficult position of potentially needing to implement this policy once more, particularly as those less well-off are more likely to be endangered by needing to venture out to work. Should shielding return, it must do so as part of an effective suppression strategy, complemented by effective testing and tracing, and followed by a protracted, cautious approach of reopening society so as not to again squander the efforts of those enduring such difficult and painful restrictions.”


Prof Mark Woolhouse, Professor of Infectious Disease Epidemiology, University of Edinburgh, said:

“The SAGE document re-makes the now well-rehearsed arguments against a ‘let it rip’ strategy that allows herd immunity to build up while vulnerable people are somehow shielded from infection. I agree with those sentiments.

“Importantly, however, the SAGE paper also makes it clear that they are not arguing against shielding in general, saying that the approach they are criticising “… stands in distinction from a policy of shielding of those who are clinically extremely vulnerable, as took place earlier in the year. Nor should this paper be taken as suggesting that older people should not take precautions to avoid becoming infected“.

“That at least brings some consistency to the debate; shielding has been part of government strategy across the UK since the beginning of the pandemic. 

“Even so, I would have liked to see SAGE make a more explicit recommendation that the government urgently takes action to help people who are vulnerable protect themselves as the second wave of COVID-19 continues to grow.

“We know who these people are (75% of deaths during the first wave occurred in a known 5% subset of the population) and we know how to protect them without asking anyone to self-isolate for a prolonged period. There is already advice for people to protect themselves to protect those who are more vulnerable, but that message needs to be widely heard. What is also needed is adequate support to enable this protection to happen, be it priority access to testing for carers or alternative accommodation for those in a household with a vulnerable person who test positive.

“SAGE members are predicting that if the current wave continues to grow then the public health burden will grow too. This is inevitable to an extent, but we are not powerless. Most of those who will, sadly, die during this second wave have yet to be infected. We can put measures in place to protect the vulnerable and reduce the toll, but we need to act quickly.”


Prof James Naismith FRS FRSE FMedSci, Director of the Rosalind Franklin Institute, and University of Oxford, said:

“The segmentation advice document reflects the science as we understand it today. It actually spells out the numbers, consequences and harms a ‘segment the vulnerable’ policy would do, even if it were possible. This is scientific document. Millions of people including key workers would have to isolate, the consequences for them and the rest of us would be severe. Since multi-generational households would have to be isolated, this would disproportionately burden the non-white population. As the document says there is no evidence for herd immunity to SARS-CoV-2.

“As a scientist, I would strongly advise Government against such a “segment the vulnerable” policy. No one likes social restrictions, they are destructive and harmful, however, they are currently the best way to reduce the toll of covid19 in the UK. It is for politicians not scientists to take decisions about what policy the country should follow and to balance competing concerns. This scientific analysis should help guide them.”


Dr Michael Head, Senior Research Fellow in Global Health, University of Southampton, said:

“This refers to segmentation, as proposed by the Great Barrington Declaration. The idea is to reach a level of herd immunity in the population by allowing the spread of COVID-19 through much of society whilst trying to protect vulnerable populations. In my opinion, it is a very bad idea.

“It is good to see a consensus statement from SAGE, reiterating that this segmentation idea is a strategy that has no place in our society. This follows on from statements by the WHO, who called the idea ‘scientifically problematic and unethical’. Other major expert groups have also refuted a segmentation strategy, including Independent SAGE, the Academy for Medical Sciences, and the many signatories of the John Snow Memorandum.

“Attempting to reach herd immunity in this way is problematic for many reasons. We have seen during a full national lockdown that vulnerable people could not be easily shielded, with a great deal of excess death. There is also the emerging evidence around long COVID, and issues of waning immunity and reinfection.

“A key argument by those in favour of herd immunity via this segmentation route is that other groups of patients have less access to healthcare, such as those suffering from cancer or stroke. However, as we are seeing in the UK right now, significant COVID-19 community transmission results in large numbers of hospitalised patients, reducing beds available for other patients and placing that huge excess burden on the health service. Strategies that suppress the virus are not just good for reducing the burden of COVID-19, they also benefit other patients too.”

References –


All our previous output on this subject can be seen at this weblink:


Declared interests

Prof Mark Woolhouse: No CoIs to declare

None others received

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