Professor, interested in plagues, and politics.
Re-locking my twitter acct when 
is 70% fully vaccinated.
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I made this figure for a talk I gave earlier today. The critical fraction to vaccinate to get to herd immunity is [1-(1/R0)]/VE, where R0 is the basic reproduction number and VE is vaccine efficacy.pic.twitter.com/abp5jTteJc
The dashed line is 100% vaccinated...we obviously can't vaccinate > 100% of the population. When we started out with R0 = 2 or 3 with OG SARS-2, herd immunity was readily attainable with VE of 70-90%.pic.twitter.com/s2jHj26sNl
Variants do two things: they push R0 up, but they also appear to push VE down, at least for some vaccine/variant combinations. That makes herd immunity harder to attain. Here's alpha (B117), which has an R0 around 40% higher than OG sars-2.pic.twitter.com/NzlZsFvXuE
Now we're dealing with delta which *may* have VE as low as 30% for a single vaccine dose (I have seen data today that suggest that that's overly pessimistic). But regardless, some estimates place delta R0 as high as 6-8. What does that do to herd immunity?pic.twitter.com/e4KpF9siNV
It makes it still harder to attain, or even unattainable. Does that mean we should throw in the towel? No. R_effective for an infectious disease, without intervention (no distancing, TTI, masks, etc) is R0 x S, where S is the fraction of the population susceptible to disease.
If we have 80% of Canadians vaccinated with a 90% effective vaccine, that means we have 28% of the population susceptible (1-(0.8x0.9)) R_effective for a disease with R0 = 6 is now 1.68. Not below 1, so we don't have herd immunity, but...
We have a disease that is MUCH easier to control than with R = 6. If we use tools at our disposal (TTI, ventilation, masks, emphasis on outdoor rather than indoor) sufficiently to reduce transmission by 40%, we are back into R < 1 territory.
Over time, safe and effective vaccines for kids will become a reality. Continuing to take COVID-19 seriously and use science (rather than wishful thinking) for control will allow a highly vaccinated population to turn the disease into an annoyance rather than a major disruptor.
Is this shit ever going to get better its exhausting.
It already is getting better, isn't it?
Any clarity on what the R0 is for the variants? This chart is kinda concerning.
OG 2-3, Alpha 3-4, Delta 6-8.
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