I am a little confused by this @nytimes reporting by @MarcSantoraNYT and @RebeccaDRobbins on the new AZD1222 data. First of all, the claim that this data is the “first” to document evidence that a COVID vaccine can result in a reduction in transmission seems to be wrong.

In fact, just last week, Israeli researchers documented a 50% reduction in both symptomatic and asymptomatic infections in individuals who took a single dose of the Pfizer mRNA shot in a retrospective cohort study. https://www.medrxiv.org/content/10.1101/2021.01.27.21250612v1.full-text

This is a preprint, but so is the new Astra data! Furthermore, the original AZD1222 publication in the Lancet in December *also* reported on preliminary PCR positivity in asymptomatic individuals in COV002 as well. https://www.thelancet.com/action/showPdf?pii=S0140-6736%2820%2932661-1

Finally, one cannot ignore the fact that despite the laudatory quotes, today’s data does not really change the basic assumptions about AZD1222 we had in December. That is, the vaccine is around 70% effective in preveting symptomatic COVID.

Reducing the dose on the prime or boost shot, or increasing the length between prime and boost *may* increase efficacy. But we note that the efficacy estimates on these alternative dosing schemes do not appear to be stat. significant different than that for the standard approach.