Let's think this through - @NSWHealth reports 1.9m vaccine doses, which based on previous figures is probably ~1.5m first and .4m second doses
With a population of 8.2m, that's about 20% of the population vaccinated at least once
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Let's assume that all of this was Astrazeneca, with an estimated vaccine efficacy (protection against infection) of somewhere around 70%, and think about some different scenarios of the reproductive number (R)
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With a standard R0 of 2.6 for COVID-19, and 20% vaccinated with AZ, we'd expect that the virus would infect about 14% fewer people on average, so our effective reproductive number (Rt) goes down to 2.2
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Now that doesn't sound like all that much, perhaps, but it is similar to the level of reduction that previous studies have seen from other interventions against COVID-19 such as school closures and the like https://www.nature.com/articles/s41586-020-2405-7#Sec2 …pic.twitter.com/gYonoD61jD
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If our R0 started at 4 (let's say a very transmissible variant) we might expect to see a reduction to about 3.4 from this level of vaccination alone
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This sort of reduction might be the difference between, say, masks stopping the outbreak entirely and needing to implement further measures
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And what if we had 40% vaccinated? Or 50%? We might not need anything other than the excellent contact tracing system we already have to keep a lid on this sort of outbreak!
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This has been your daily thread of why you should all go and get your vaccines, specific to NSW Australia but also for everyone else because the same thing applies no matter where you live
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Also, worth noting that at a vaccination rate of 70%, even if you assume Astrazeneca is only 70% effective, you're looking at about a 50% reduction in R0 which means that contact tracing will probably be enough to completely prevent any outbreaks
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Replying to @GidMK
Isn’t that a big assumption? How effective is AZ after a single dose against Delta strain? I thought data suggests not very, and it’s suspected that’s the whole issue with the UK - widespread single dose AZ rollout to fight Alpha not so good against Delta…
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Well, in this context contact tracing has generally been enough to control minor outbreaks without significant reimposition of restrictions with the 'wild' strain. Even if AZ is only 50% against Delta, it would still probably reduce Rt enough to stop spread
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Replying to @GidMK
I'm not sure it's even looking 50% though is it? (Acknowledging the uncertainty still present of course): https://www.bmj.com/content/373/bmj.n1346 …pic.twitter.com/YjuaoykYL8
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Not to suggest anything about vaccine choice (same issue with Pfizer - UK data suggests single doses of both not that effective against Delta I think). Just mean re: vaccines having an effect on the current NSW outbreak. Still I mean I hope so obviously.
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