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Covid 19 Vaccination: One Dose or Two ?

I am going to write more on the topic of Covid 19 vaccines. I will argue that it would be better to give second (booster) shots only when vaccine supplies are plentiful. I think that so long as the vaccine is in short supply, people should be given one dose. I criticise the current policy of withholding vaccine to make sure that everyone who gets a first dose gets the scheduled booster either 3 weeks later (for the Pfizer vaccine) or 4 weeks later (for the Moderna vaccine). I argue that more lives will be saved with the one dose until supplies are plentiful strategy (even if many people don’t show up for the booster when supplies are plentiful). I think that the current policy will lead to tens of thousands of un-necessary deaths in the US alone with worse consequences for countries further back in line for vaccine supplies.

The post will have two sections. One will be an attempt to analyse the published data, which are mostly Kaplan and Meier plots with numbers read off by eyeballing. I will conclude that the best (poor) estimate of the reduction of infections from the first dose is more than 18 times the reduction due to the second dose. This calculation requires the key unproven assumption that the effect of one shot is weaker than but as durable as the effect of two shots.

This would mean that efficient deployment is one dose for as many as possible as soon as possible and second doses when giving them doesn’t interfere with this. I will go on to bore people with some p-values. I think that the null that it is as efficient to give second doses on schedule is rejected at at the 5% level (given published data). I note that benefits probably include the (unproven) prevention of transmission as well as benefits for the vaccinated people. I also note that giving two to some and zero to others is unfair especially given the difficulty of deciding who gets vaccinated first and the necessarily partly arbitrary decisions. The second section will come back to arguing about public policy and ethics as I just did.