Risk transmission

Lockdown for the many or the few: when experts disagree!

Yesterday two groups of scientists sent conflicting open letters to those leading the national responses to the increasing number of cases in the 4 countries of the UK.  The issues raised in these letters are relevant to how other countries/regions in Europe, North America and beyond manage the outbreak. When scientists disagree, the public loses confidence in their opinion and governments are left wondering whose advice  to follow.

In this post I dissect the points raised and attempt to reconcile the different conclusions as to what  countries should do.

The 2 letters:

  • Both were led by epidemiology colleagues from Oxford University who work in the same department of Primary Care
  • The first arguing for a whole population approach was led by Professor Trish Greenhalgh which said:
    • Restrictions in terms of social distancing/lockdown should apply to everyone because:
    • Including everyone is the best way to reduce the incidence of infection 
    • There is too much uncertainty to have a targeted approach 
  • The second arguing for a targeted approach was led by Professor Carl Heneghan which said:
    • Restrictions in terms of social distancing/lockdown should apply to those who are the most vulnerable, such as the elderly because:
    • Limiting actions to contain the virus  to those for whom there is clear evidence that there is a measurable benefit 
    • In this way we minimise unnecessary harmful impacts on the economy, mental health and education 

Critique of the Greenhalgh letter 

Point made in the letterMy response
Everyone in the  population is at some risk:  even young people can have complications and long term health problemsIt is a ‘numbers game’ and the low rate of serious complications (for example) in young people should be taken into consideration
Cannot easily have different policies for vulnerable and non-vulnerable.  Example -grandparents often involved in child careThe data from several countries would suggest that the recent increasing incidence has been greater in younger people.  This suggests that shielding works
The letter argued against the targeted policy – that if a sufficient proportion of low risk people get infected – this  would lead to a degree of herd immunity.  This would then protect the (say) older people who have been shielding.   This letter argued that that such policy is flawed – based on the assumption that people cannot get re-infected, for which there is no evidence  The rates of a second infection thus far are very very low so it is plausible that we could achieve herd immunity whilst protecting the vulnerable.  But I agree that the achievement of herd immunity is unlikely to come from natural infection rather than vaccine
No evidence from other countries that having targeting policies is more effective than general restrictionsThis is true, but  it is probably unrealistic to expect to obtain definitive evidence.  The authors also write (next point) that we should not necessarily require such evidence 
Relying on high quality research on a single aspect to make decisions in a situation as complex as managing Covid-19 is dangerous and need to take a more balanced viewI don’t disagree

Critique of the Heneghan letter 

Point made in the letterMy response 
Current UK government policy does not have a clearly stated overall strategy, so impossible to judge if any policy is successful I agree, but not sure how we would reach agreement on what that policy should be
Having a policy just focusing on reducing deaths is too restrictedI am not sure that a policy of just reducing deaths has been stated. One problem is that deaths are the most easily measured and so the media in these situations focus on comparing death rates both within and between countries 
Mortality is concentrated in older people and those with pre-existing health problems. Therefore, this is the group that should be targeted for interventionsThe authors are arguing both ways on this, they argue above against focusing on those at increased risk of dying if they get Covid-19. 
Blanket lockdown policies on the whole population which are ‘unnecessary’ can as a side effect result in a reduced access to health care for non-Covid-19 diseases.  This can  lead, for example, to increased numbers with untreated heart disease or cancerI think this is a significant concern and countries will need to provide robust data on the consequence of lockdown on health care for other diseases.  But this is not a ‘zero sum’ game; ie countries can have high levels of lockdown for the general population and invest heavily in maintaining health care more widely
A previously widely discusused point on the economic costs of lockdown and that, for example the unemployment and other consequences have their substantial health risksThis has to be true, or at the very least is a testable hypothesis.  The results from available national data will take several months to gather.  Further, these health consequences may take decades and not just months to become apparent 


  • No-one suggests this is easy and the trade-off between the harmful impacts of Covid-19 and of strict lockdown are well known I am sure to all readers of this blog
  • These two open letters also identify that despite the fact we are 9 months into the pandemic, there are still so many unknowns
  • Not surprisingly there is scope for disagreement on interpretation of the available evidence 
  • These letters do bring into focus what are the key issues 
  • If I were forced to judge which letter provides the stronger argument, it would be that the targeted approach is likely to  win out in terms of the sum total effects on human health in our populations 

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