Michael Ejercito
2024-10-21 01:14:48 UTC
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PermalinkVaccinating care home residents reduced deaths, but the effect was small
– new study
Published: October 18, 2024 8:42am EDT
Authors
David Paton
Chair of Industrial Economics, Nottingham University Business School,
University of Nottingham
Sourafel Girma
Professor of Industrial Economics, Faculty of Social Sciences,
University of Nottingham
Disclosure statement
David Paton is a member of HART (Health Advisory and Recovery Team).
Sourafel Girma does not work for, consult, own shares in or receive
funding from any company or organization that would benefit from this
article, and has disclosed no relevant affiliations beyond their
academic appointment.
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Vaccinating older people probably did avert some deaths in 2021, but the
effects were small. And even those small effects on mortality seem to
have dissipated during the booster programme. That’s the conclusion of
our new study, published in the European Economic Review.
COVID-related deaths decreased significantly in most of Europe and the
US from the middle of 2021. Although this reduction coincided with the
rollout of COVID vaccines, it has proved surprisingly difficult to
identify the extent to which vaccination contributed to the drop in deaths.
Randomised controlled trials (the gold standard for testing new
treatments) suggest COVID vaccination can provide significant protection
against serious illness and death relative to unvaccinated people who
have not previously been infected with COVID. But there are reasons the
effect of vaccination on mortality may be lower when viewed outside of
trials.
Early in the programme, there were hopes that vaccination would also
prove highly effective in preventing the spread of COVID but it has
since become clear that vaccination provides only limited and short-term
protection against infection and transmission.
Don’t let yourself be misled. Understand issues with help from experts
It is also well established that a previous infection provides
protection both against reinfection and against serious illness and
death in the event of reinfection that is at least as effective as
vaccination. Having a previous infection significantly reduces the
likelihood of being vaccinated meaning the vaccinated population will
include a relatively high proportion of people without protection from
prior infection. So even if vaccination provides protection at an
individual level, we may still observe population-level mortality rates
that are similar for vaccinated and unvaccinated groups.
The effectiveness of vaccination programmes may also be limited by
people’s behaviour. For example, there is evidence that vaccinated
people who get infected are more likely to have mild symptoms and this
may cause them to take fewer precautions than others against spreading
infection. As a result, vaccination may sometimes be associated with
more rather than less transmission.
Taken together, even if vaccination reduces the risk on an individual
basis, it does not necessarily follow that it will reduce deaths at a
population level. Existing research reflects this ambiguity with some
research finding very significant effects of vaccination on death while
other findings conclude there was little or no effect at all.
Our new study attempts to improve our knowledge about the effect of
COVID vaccination programmes by estimating the effect of vaccination
take up on deaths in care homes. This is a particularly important group
to examine. Given that the vast majority of COVID-related deaths occur
in the elderly, any effect on deaths is highly likely to be seen in care
homes.
An ampoule of AstraZeneca vaccine with a syringe.
COVID vaccines reduced serious illness and deaths, but they did little
to stop infection and transmission. Marc Bruxelle /Alamy Stock Photo
Machine learning used to analyse the data
We examined deaths from COVID in care homes across nearly 150 local
authorities in England from the start of the vaccine rollout in December
2020 until after the second booster dose in summer 2022. We tested
whether higher rates of vaccination of staff and elderly residents led
to fewer deaths both in total and from COVID.
One feature of our research is the use of machine learning (a type of
artificial intelligence) to isolate the effect of vaccination from other
factors that may also have affected mortality including levels of prior
infection as well as demographic, economic and health differences among
local authorities.
Machine learning is particularly adept at separating out the effects of
a high number of potential explanatory variables, providing much better
evidence of when associations represent true causal relationships. In
contrast to some other research, we also use a measure of vaccination
that takes account of the fact that effectiveness wanes over time.
We found that higher vaccination rates of residents (but not of staff)
did indeed lead to fewer deaths, but the effect was relatively small.
For example, an increase in the resident vaccination take-up rate of 10%
in a local authority caused, on average, a reduction of 1% in the total
care home mortality rate. That is equivalent to about 22 fewer deaths
per week nationwide.
Of course, any reduction in deaths is welcome. But vaccination does not
appear to be the key factor in reducing care home deaths from COVID. We
also found that the reduction in deaths was restricted to the initial
vaccination rollout.
From September 2021, when the booster vaccination programme started in
England, higher vaccination rates of elderly residents do not seem to
have led to any reduction in deaths. Based on these results, vaccination
is unlikely to have been responsible for the sustained fall in
COVID-related deaths.
Why then did Europe and the US experience large reductions in COVID
deaths since 2021, even during times when infection rates have soared?
There are two explanations. The first is the growth of variants such as
omicron that, although highly infectious, are less deadly than variants
responsible for the early waves.
Second, is the rise in the cumulative number of people who gained
protection from having had previous infections.
These explanations are consistent with the experience of places such as
Hong Kong, New Zealand and Taiwan. All saw relatively low COVID
infections and deaths in 2020, meaning only limited levels of natural
immunity had been built up. All then experienced high mortality rates
during 2022, well after most people in those places had been vaccinated.
For example, the seven-day average mortality rate in Hong Kong reached
40 deaths per million in March 2022, a rate far above the highest peak
seen in the US during the whole pandemic despite cumulative vaccination
rates at that time being similar.
Even though vaccination probably reduced care home deaths by a small
amount in the early rollout period, there is little evidence that the
booster programme had any significant effect on COVID-related deaths.