'Shielding' strategies instead of lockdowns would have led to tens of thousands more deaths, new modelling shows

Date:
April 26, 2022
Source:
University of Bath
Summary:
Shielding vulnerable people while allowing Covid-19 to run through
the rest of the population had been proposed as an alternative
strategy to lockdowns. Modelling by University of Bath scientists
shows it would ultimately have failed as infections 'leak through'
to the most vulnerable. Even in the most optimistic shielding
scenario, critical care capacity in hospitals would have been
massively exceeded with tens of thousands of unnecessary deaths.



FULL STORY ========================================================================== Shielding those vulnerable to COVID-19, while allowing the virus to
spread, largely unmitigated, through the rest of the population, would
have failed according to a new modelling paper published today in PLOS
Global Public Healthby University of Bath scientists.


========================================================================== Shielding strategies or "focused protection," as advocated for in the
Great Barrington Declaration, would have been impossible to implement
in practice and would have likely led to far worse outcomes. Even if implemented perfectly, the modelling reveals that allowing the infection
to spread through less vulnerable groups prior to vaccination would have overwhelmed health care capacity in the UK and led to tens of thousands
of unnecessary deaths. In reality, practical considerations would have
meant that large numbers of vulnerable people who were supposed to be
protected would also have died.

The unprecedented scale of the public health crisis posed by the COVID-19 pandemic forced governments around the world to impose restrictions on
social contact to suppress transmission of the coronavirus. However,
the social and economic costs of these measures, especially lockdowns,
have been high, drawing substantial opposition from some sections of the
media, members of the public, and a small, but vocal group of scientists.

An alternative and widely discussed strategy would have been to
temporarily focus protection on ("shield") those who were most vulnerable
to COVID-19 (the elderly and those with certain pre-existing conditions),
with the aim of achieving herd immunity by allowing a largely unmitigated epidemic in the rest of the population. However, this approach has
received little scrutiny in the form of mathematical modelling.

In this new study, published today, the researchers assessed a
hypothetical large city in England with a population of 1 million
inhabitants, using an SEIR (Susceptible, Exposed, Infected, Removed)
model. They compared the outcomes from no shielding, with imperfect and
perfect shielding, with shielding restrictions lifted when cases fall
below a given threshold.

The research concludes that while shielding may have protected the
vulnerable in theory, it required extremely restrictive conditions that
were impossible to achieve in practice. For example, because shielding in
real populations would have been imperfect, infections in the lower-risk population would have leaked through to vulnerable people who were
shielding. In addition, if lower-risk individuals reduced social contact
to avoid infection it may have been impossible to achieve herd immunity, meaning a second wave of infections would have occurred after shielding
had ended. Even if herd immunity was achieved, care homes would still
have been at risk of local outbreaks because immunity would have been
unevenly distributed in the population.



==========================================================================
To be effective, shielding would have required those who were at higher
risk to not only be rapidly and accurately identified, but also to shield themselves for an indefinite period, rendering the strategy impractical to implement. The modelling also suggests that in even the most optimistic shielding scenario, critical care capacity in hospitals would have been exceeded at least ten-fold at the peak of the outbreak. This is not to
mention the huge healthcare burden associated with the large number
of cases of long covid that would result from mass infection. Waning
immunity, and new immunity-evading variants would only have served to
make a shielding-only strategy even more untenable.

Although vaccines are now available and have been successfully rolled
out in many countries, modelling studies such as this are critical to
determine whether shielding would have been a viable strategy for dealing
with COVID-19, or, indeed, the next pandemic. Many countries have poor
vaccine coverage and so the choice between shielding and measures that
are more restrictive at a population level is likely to remain for some
time. In future, new variants may continue to emerge that are able to
escape immunity, which may require a renewed choice between lockdowns
and shielding.

In summary, the new study exposes critical weaknesses of shielding (or
focused protection): even with the most optimistic assumptions, tens
of thousands of lower-risk individuals would have died and critical
care capacity would have been rapidly exceeded. With more realistic assumptions, shielding would have failed to protect the most vulnerable, achieving little more protection than an unmitigated epidemic.

Dr Kit Yates, senior lecturer in the Department of Mathematical Sciences
at the University of Bath and one of the study's authors, explains:
"Our study shows how misguided the idea of shielding the vulnerable and
letting the virus rip through the rest of the population would have been.

"Even if we could have managed perfect shielding, our healthcare system
would still have been quickly overwhelmed. In reality, some inevitable leakiness in the shielding system would almost certainly have led to big outbreaks amongst the vulnerable and resulted in huge numbers of deaths
as well." Dr Cameron Smith, another of the study's authors, added:
"Our model captures some important features which represent how immunity
is likely to be distributed in the population. As a consequence of this heterogeneity, potential shielding strategies would have had limited
success in reducing the number of deaths." Dr Ben Ashby, the study's
other author said: "Despite the success of the vaccination programme,
the recent omicron wave shows that we are not out of the woods yet. If in future a new variant emerges that substantially escapes existing immunity,
then it's possible we may have to choose between lockdowns and shielding
once again (or indeed, in future pandemics). Although lockdowns are costly
for many reasons, attempting to shield the vulnerable while letting the
virus spread through the rest of the population is far worse."

========================================================================== Story Source: Materials provided by University_of_Bath. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Cameron A. Smith, Christian A. Yates, Ben Ashby. Critical
weaknesses in
shielding strategies for COVID-19. PLOS Global Public Health,
2022; 2 (4): e0000298 DOI: 10.1371/journal.pgph.0000298 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/04/220426153614.htm

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