Objectives The early stages of the COVID-19 pandemic
illustrated that SARS-CoV-2, the virus that causes the
disease, has the potential to spread exponentially.
Therefore, as long as a substantial proportion of the
population remains susceptible to infection, the potential
for new epidemic waves persists even in settings with low
numbers of active COVID-19 infections, unless sufficient
countermeasures are in place. We aim to quantify
vulnerability to resurgences in COVID-19 transmission
under variations in the levels of testing, tracing and mask
Setting The Australian state of New South Wales (NSW),
a setting with prolonged low transmission, high mobility,
non-universal mask usage and a well-functioning testand-trace system.
Participants None (simulation study).
Results We find that the relative impact of masks is
greatest when testing and tracing rates are lower and
vice versa. Scenarios with very high testing rates (90% of
people with symptoms, plus 90% of people with a known
history of contact with a confirmed case) were estimated
to lead to a robustly controlled epidemic. However, across
comparable levels of mask uptake and contact tracing,
the number of infections over this period was projected to
be 2–3 times higher if the testing rate was 80% instead
of 90%, 8–12 times higher if the testing rate was 65%
or 30–50 times higher with a 50% testing rate. In reality,
NSW diagnosed 254 locally acquired cases over this
period, an outcome that had a moderate probability in the
model (10%–18%) assuming low mask uptake (0%–25%),
even in the presence of extremely high testing (90%) and
near-perfect community contact tracing (75%–100%), and
a considerably higher probability if testing or tracing were
at lower levels.
Conclusions Our work suggests that testing, tracing
and masks can all be effective means of controlling
transmission. A multifaceted strategy that combines
all three, alongside continued hygiene and distancing
protocols, is likely to be the most robust means of
controlling transmission of SARS-CoV-2.
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