Math Time – Delta Edition

An update to my previous mathematical analysis of covid transmission now that I’ve seen R0 estimates for this delta variant …

The R0 value for the delta variant seems to be between 5 and 8. Looks like just over 46% of the US population is vaccinated. The vaccines are published as being 90-something percent effective. That makes an effective transmission rate between (5 * (1- (0.46 * 0.95))) and (8 * (1- (0.46 * 0.9))). Between 2.9 and 4.7 — somewhat surprising given the R0 of slightly under 3 that was published at the start of the SARS-CoV-2 outbreak. That means that, as health orders and mandates are lifted, we’re basically exactly where we were a year ago even though about half the population is vaccinated.

A mathematically interesting thing — if you could get the vaccine efficacy up to 100% (a third shot, a tenth shot, a different vaccine, whatever)? We’d still have an effective transmission rate between 2.7 and 4.3 — the value goes down, but not significantly. On the other hand, increasing the percentage of fully vaccinated individuals by 10% gives us an effective rate of transmission between 2.5 and 4.0. Having 70% of the population vaccinated would yield an effective rate of transmission between 1.8 and 3.0. We’d need to get somewhere between 90 and 98% of the population vaccinated to bring the delta variant’s effective rate down below 1 (the point where it would die out naturally)!

That tells me this virus is going to be around for a long time — especially since the R0 for some upcoming variants might be higher. Also, I’m curious to see if the government authorizes a third dose given the minimal impact increasing efficacy has on the effective rate of spread.

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