New modelling shows 83 per cent of all New
Zealanders need to be vaccinated against Covid-19 before we
can safely remove public health restrictions.
estimate is based on data from earlier variants of the
virus, so the percentage may need to be even higher now with
faster-spreading variants. Te
Pnaha Matatini scientists say it means public
health measures like masks, Alert Levels, and border
restrictions will need to remain in place for the vaccine
The SMC asked experts to comment on the
Dr Rawiri McKree Jansen (Ngati Raukawa,
Ngati Hinerangi), Clinical Director, National Hauora
Coalition, comments:
The paper addresses an
important issue for Aotearoa. So far our pandemic response
has achieved significant success and has largely protected
communities from severe illness and death from Covid. The
vaccination programme can contribute further protections,
indeed must contribute further protections before the
borders are opened.
The authors note that
communities with relatively low vaccine coverage or
high contact rates will remain vulnerable to major
outbreaks. Mori communities are exposed to both of these
risks currently with a vaccination programme that is
underperforming in terms of equity. The paper is a timely
provocation to ensure that a pro-equity vaccination
programme is resourced.
Until vaccination rates in
the order of 90% of eligible Mori are achieved, opening of
the borders would likely be
Conflict of interest statement:
I am a member of the Expert Panel for Stuffs The
Whole Truth Covid-19 Vaccination editorial
Associate Professor Malcolm Campbell,
GeoHealth Laboratory, University of Canterbury,
In essence, the key message from this
paper is that more vaccinated people is better for all of
us. We need to reach herd immunity, the protection
that comes from immunity through successful vaccination or
from previous infection. The modelling also shows that
vaccination leads to fewer hospitalisations and
As we get closer to herd immunity,
there is a chance of a new normal emerging. However, we
still need to vaccinate as many people as we can, at least 4
out of 5, and some of the modelled scenarios give us a clear
signal that a new normal may not be as close as we
might think. This is especially important if lots of us
arent vaccinated and a highly transmissible variant
emerges. Even once we are vaccinated, we still need to
carefully think about following public health messages and
As with any model, the assumptions
scientists make are key to understanding the results. Often,
assumptions change or evolve as more evidence emerges,
allowing models to be refined. This means that models
arent right or wrong but based on the best
evidence at a point in time under uncertain circumstances.
For example, new variants of the virus may well change any
modelling assumptions. This is a relatively normal part of
the modelling process. At present, the models of the unequal
coverage of vaccine by socio-economic group or by local
geographies across NZ, havent been developed as this is
even more complex.
No conflict of interest
Professor Peter McIntyre, medical
advisor, Immunisation Advisory Centre,
This is a valuable study by a highly
experienced modelling group. Its most important message is
whether or not New Zealand reaches a theoretical
population immunity threshold, the higher vaccination
coverage is, the more protection the population has
collectively against COVID-19, and the easier it will
become to control outbreaks.
However, a
limitation of the study, which leads to some unnecessarily
scary conclusions, is that it looks at a scenario that is
very unlikely in practice, i.e. opening up the border
without restrictions and modelling on five infected people
entering daily for two years. The actual situation will
almost certainly be that borders will open only in the
context of high vaccine coverage and include entry
conditions such as pre-testing and proof of vaccination
status this will give much more favourable outcomes than
the authors suggest.
We strongly agree with the
authors that it will be essential to continue to
vaccinate as many people as possible to minimise the
combined potential for transmission and health impacts
and that until the vaccine rollout is complete, retaining
the elimination strategy will protect people who have not
yet been vaccinated and decrease use of the alert level
However, we would like to see
further refinement of this valuable model and its
assumptions to better reflect the lowered risk of severe
disease when there is high vaccine coverage in New Zealand
and borders are cautiously opened to limited arrivals. This
should better reflect the real-world experience of countries
such as the UK and Israel, within the context of some
community transmission and taking into consideration the
reduction in severity of cases occurring in vaccinated
people due to breakthrough infections. We can be confident
that severe cases will be uncommon in a high vaccine
coverage future.
No conflict of interest
Andrew Sporle, Senior Research Fellow
(Honorary), Department of Statistics, University of
Auckland, comments:
This new modelling demonstrates
how important it will be to protect those at higher risk of
infection and poor outcomes as the vaccine rollout
continues. Groups with more people who cant get
vaccinated due to age or health issues will need higher
levels of vaccine coverage to prevent deaths and
We already know that Mori and
Pacific people have had much worse outcomes from the current
epidemic. Those populations also have much larger
proportions of their population who arent old enough for
vaccination or who have pre-existing conditions. While
improving the vaccination coverage for Mori and Pacific
adults needs to be urgently addressed, there also needs to
be increased support for local initiatives to protect local
communities and improving contact tracing in case of an
Conflict of interest statement:
Andrew Sporle is a social statistician who works with Te
Pnaha Matatini and other groups on COVID-19 outcomes and
vaccination modelling as well as disinformation sources. He
was not involved in the work for this particular
Professor Mick Roberts, Professor in
Mathematical Biology, Massey University,
The reopening of New Zealands borders
makes it inevitable that some persons infected with Covid-19
will enter the country. The concept of herd immunity means
that, on average, each infected person would infect less
than one other person, and therefore a major outbreak would
be prevented. The only way to achieve herd immunity (without
having a major outbreak) is by achieving a high level of
vaccination coverage.
A new model from Te Pnaha
Matatini calculates the vaccine coverage needed to achieve
herd immunity in New Zealand. The model is deterministic and
age structured, but still relies on best-guess estimates of
parameter values, some of which are poorly known. The model
suggests that if the basic reproduction number is 4.5 (alpha
variant) or 6.0 (delta variant) then vaccine coverage needs
to be 83% or 97% respectively. Using a standard back of
the envelope rule the results would be 85% and 91%
respectively. These are overall population estimates, so if
those under 15 years old are not protected, the higher
figure is not attainable. Mask wearing, testing and tracing
will be necessary for some time yet.
No conflict
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