I have argued for delaying the second dose in order to hit the virus hard and get more people the first dose. Now epidemiologist @michaelmina_lab and @zeynep make the case in the NYTimes. I want to add two points to their analysis.... https://www.nytimes.com/2020/12/18/opinion/coronavirus-vaccine-doses.html 1/3

First, we may be able to mix and match vaccines. A first dose of an mRNA and a second dose of say AZ. Mix and match could be better at stimulating the immune system and could help to alleviate supply constraints. The British are running a trial on this question. 2/3

Second, @michaelmina_lab & @zeynep don't deal with the econ but we need to make sure that Pfizer and Moderna are compensated for running more clinical trials and for potentially reducing their sales. That's cheap but incentives matter.